A cephalopod (/ˈsɛfələpɒd, ˈkɛf-/) is any member of the
molluscan class Cephalopoda (Greek plural κεφαλόποδα,
kephalópoda; "head-feet") such as a squid, octopus or nautilus. These
exclusively marine animals are characterized by bilateral body
symmetry, a prominent head, and a set of arms or tentacles (muscular
hydrostats) modified from the primitive molluscan foot. Fishermen
sometimes call them inkfish, referring to their common ability to
squirt ink. The study of cephalopods is a branch of malacology known
Cephalopods became dominant during the
Ordovician period, represented
by primitive nautiloids. The class now contains two, only distantly
related, extant subclasses: Coleoidea, which includes octopuses,
squid, and cuttlefish; and Nautiloidea, represented by
Allonautilus. In the Coleoidea, the molluscan shell has been
internalized or is absent, whereas in the Nautiloidea, the external
shell remains. About 800 living species of cephalopods have been
identified. Two important extinct taxa are the
Nervous system and behavior
2.3 Use of light
2.6 Circulatory system
2.8 Locomotion and buoyancy
2.10 Head appendages
2.12 Excretory system
2.13 Reproduction and life cycle
2.13.1 Sexual maturity
2.13.3 Male-male competition
2.13.4 Mate choice
2.13.5 Sexual dimorphism
3.2.1 Suprafamilial classification of the Treatise
3.2.2 Shevyrev classification
3.3 Cladistic classification
3.3.1 Monophyly of coeloids
4 In popular culture
5 See also
8 Further reading
9 External links
Left: A pair of
Sepia officinalis in shallow water
Benthoctopus sp. on the
Davidson Seamount at 2,422 m depth
There are over 800 extant species of cephalopod, although new
species continue to be described. An estimated 11,000 extinct taxa
have been described, although the soft-bodied nature of cephalopods
means they are not easily fossilised.
Cephalopods are found in all the oceans of Earth. None of them can
tolerate freshwater, but the brief squid, Lolliguncula brevis, found
in Chesapeake Bay, is a notable partial exception in that it tolerates
brackish water. Cephalopods are thought to be unable to live in
freshwater due to multiple biochemical constraints, and in their
+400 million year existence have never ventured into fully
Cephalopods occupy most of the depth of the ocean, from the abyssal
plain to the sea surface. Their diversity is greatest near the equator
(~40 species retrieved in nets at 11°N by a diversity study) and
decreases towards the poles (~5 species captured at 60°N).
Nervous system and behavior
Cephalopod intelligence, squid giant axon, squid giant
synapse, and cephalopod aggression
Left: An octopus opening a container with a screw cap
Right: Hawaiian bobtail squid, Euprymna scolopes, burying itself in
the sand, leaving only the eyes exposed
Cephalopods are widely regarded as the most intelligent of the
invertebrates, and have well developed senses and large brains (larger
than those of gastropods). The nervous system of cephalopods is the
most complex of the invertebrates and their brain-to-body-mass
ratio falls between that of endothermic and ectothermic
vertebrates.:14 Captive cephalopods have also been known to climb
out of their aquaria, maneuver a distance of the lab floor, enter
another aquarium to feed on the crabs, and return to their own
The brain is protected in a cartilaginous cranium. The giant nerve
fibers of the cephalopod mantle have been widely used for many years
as experimental material in neurophysiology; their large diameter (due
to lack of myelination) makes them relatively easy to study compared
with other animals.
Many cephalopods are social creatures; when isolated from their own
kind, some species have been observed shoaling with fish.
Some cephalopods are able to fly through the air for distances of up
to 50 m. While cephalopods are not particularly aerodynamic, they
achieve these impressive ranges by jet-propulsion; water continues to
be expelled from the funnel while the organism is in the air. The
animals spread their fins and tentacles to form wings and actively
control lift force with body posture. One species, Todarodes
pacificus, has been observed spreading tentacles in a flat fan shape
with a mucus film between the individual tentacles while
Sepioteuthis sepioidea, has been observed putting the
tentacles in a circular arrangement.
Cephalopods have advanced vision, can detect gravity with statocysts,
and have a variety of chemical sense organs.:34 Octopuses use their
arms to explore their environment and can use them for depth
Cephalopod eye and mollusc eye
The primitive nautilus eye functions similarly to a pinhole camera.
The W-shaped pupil of the cuttlefish expanding when the lights are
Most cephalopods rely on vision to detect predators and prey, and to
communicate with one another. Consequently, cephalopod vision is
acute: training experiments have shown that the common octopus can
distinguish the brightness, size, shape, and horizontal or vertical
orientation of objects. The morphological construction gives
cephalopod eyes the same performance as sharks'; however, their
construction differs, as cephalopods lack a cornea, and have an
everted retina. Cephalopods' eyes are also sensitive to the plane
of polarization of light. Unlike many other cephalopods,
nautiluses do not have good vision; their eye structure is highly
developed, but lacks a solid lens. They have a simple "pinhole" eye
through which water can pass. Instead of vision, the animal is thought
to use olfaction as the primary sense for foraging, as well as
locating or identifying potential mates.
A cuttlefish with W-shaped pupils which may help them discriminate
Surprisingly, given their ability to change color, all octopodes
and most cephalopods are considered to be color blind. Coleoid
cephalopods (octopus, squid, cuttlefish) have a single photoreceptor
type and lack the ability to determine color by comparing detected
photon intensity across multiple spectral channels. When camouflaging
themselves, they use their chromatophores to change brightness and
pattern according to the background they see, but their ability to
match the specific color of a background may come from cells such as
iridophores and leucophores that reflect light from the
environment. They also produce visual pigments throughout their
body, and may sense light levels directly from their body.
Evidence of color vision has been found in the sparkling enope squid
(Watasenia scintillans), which achieves color vision by the
use of three distinct retinal molecules (A1, sensitive to red; A2, to
purple, and A4, to yellow?) which bind to its opsin.
In 2015, a novel mechanism for spectral discrimination in cephalopods
was described. This relies on the exploitation of chromatic aberration
(wavelength-dependence of focal length). Numerical modeling shows that
chromatic aberration can yield useful chromatic information through
the dependence of image acuity on accommodation. The unusual off-axis
slit and annular pupil shapes in cephalopods enhance this ability.
In 2015, molecular evidence was published indicating that cephalopod
chromatophores are photosensitive; reverse transcription polymerase
chain reactions (RT-PCR) revealed transcripts encoding rhodopsin and
retinochrome within the retinas and skin of the longfin inshore squid
(Doryteuthis pealeii), and the common cuttlefish (Sepia officinalis)
and broadclub cuttlefish (Sepia latimanus). The authors claim this is
the first evidence that cephalopod dermal tissues may possess the
required combination of molecules to respond to light.
Some squids have been shown to detect sound using their
Use of light
This broadclub cuttlefish (Sepia latimanus) can change from camouflage
tans and browns (top) to yellow with dark highlights (bottom) in less
than a second.
Further information: Counter-illumination
Most cephalopods possess an assemblage of skin components that
interact with light. These may include iridophores, leucophores,
chromatophores and (in some species) photophores.
colored pigment cells that expand and contract in accordance to
produce color and pattern which they can use in a startling array of
fashions. As well as providing camouflage with their
background, some cephalopods bioluminesce, shining light downwards to
disguise their shadows from any predators that may lurk below. The
bioluminescence is produced by bacterial symbionts; the host
cephalopod is able to detect the light produced by these
Bioluminescence may also be used to entice prey, and
some species use colorful displays to impress mates, startle
predators, or even communicate with one another.
Animal coloration and Category:Animals that can
Cephalopods can change their colors and patterns in milliseconds,
whether for signalling (both within the species and for warning) or
active camouflage, as their chromatophores are expanded or
contracted. Although color changes appear to rely primarily on
vision input, there is evidence that skin cells, specifically
chromatophores, can detect light and adjust to light conditions
independently of the eyes. Coloration is typically stronger in
near-shore species than those living in the open ocean, whose
functions tend to be restricted to disruptive camouflage.:2
Evidence of original coloration has been detected in cephalopod
fossils dating as far back as the Silurian; these orthoconic
individuals bore concentric stripes, which are thought to have served
Devonian cephalopods bear more complex color
patterns, of unknown function.
Cephalopod ink and ink sac
With the exception of the
Nautilidae and the species of octopus
belonging to the suborder Cirrina, all known cephalopods have an
ink sac, which can be used to expel a cloud of dark ink to confuse
predators. This sac is a muscular bag which originated as an
extension of the hind gut. It lies beneath the gut and opens into the
anus, into which its contents – almost pure melanin – can be
squirted; its proximity to the base of the funnel means the ink can be
distributed by ejected water as the cephalopod uses its jet
propulsion. The ejected cloud of melanin is usually mixed, upon
expulsion, with mucus, produced elsewhere in the mantle, and therefore
forms a thick cloud, resulting in visual (and possibly chemosensory)
impairment of the predator, like a smokescreen. However, a more
sophisticated behaviour has been observed, in which the cephalopod
releases a cloud, with a greater mucus content, that approximately
resembles the cephalopod that released it (this decoy is referred to
as a Pseudomorph). This strategy often results in the predator
attacking the pseudomorph, rather than its rapidly departing prey.
For more information, see Inking behaviors.
The ink sac of cephalopods has led to a common name of "inkfish",
formerly the pen-and-ink fish.
Viscera of Chtenopteryx sicula
Viscera of Ocythoe tuberculata
Cephalopods are the only mollusks with a closed circulatory system.
Coleoids have two gill hearts (also known as branchial hearts) that
move blood through the capillaries of the gills. A single systemic
heart then pumps the oxygenated blood through the rest of the
Like most molluscs, cephalopods use hemocyanin, a copper-containing
protein, rather than hemoglobin, to transport oxygen. As a result,
their blood is colorless when deoxygenated and turns blue when exposed
Cephalopods exchange gases with the seawater by forcing water through
their gills, which are attached to the roof of the
organism.:488 Water enters the mantle cavity on the outside of
the gills, and the entrance of the mantle cavity closes. When the
mantle contracts, water is forced through the gills, which lie between
the mantle cavity and the funnel. The water's expulsion through the
funnel can be used to power jet propulsion. The gills, which are much
more efficient than those of other molluscs, are attached to the
ventral surface of the mantle cavity. There is a trade-off with
gill size regarding lifestyle. To achieve fast speeds, gills need to
be small – water will be passed through them quickly when energy is
needed, compensating for their small size. However, organisms which
spend most of their time moving slowly along the bottom do not
naturally pass much water through their cavity for locomotion; thus
they have larger gills, along with complex systems to ensure that
water is constantly washing through their gills, even when the
organism is stationary. The water flow is controlled by
contractions of the radial and circular mantle cavity muscles.
The gills of cephalopods are supported by a skeleton of robust fibrous
proteins; the lack of mucopolysaccharides distinguishes this matrix
from cartilage. The gills are also thought to be involved in
excretion, with NH4+ being swapped with K+ from the seawater.
Locomotion and buoyancy
Octopuses swim headfirst, with arms trailing behind
While most cephalopods can move by jet propulsion, this is a very
energy-consuming way to travel compared to the tail propulsion used by
fish. The efficiency of a propellor-driven waterjet (i.e. Froude
efficiency) is a more efficient model than rocket efficiency. The
relative efficiency of jet propulsion decreases further as animal size
increases; paralarvae are far more efficient than juvenile and adult
individuals. Since the
Paleozoic era, as competition with fish
produced an environment where efficient motion was crucial to
survival, jet propulsion has taken a back role, with fins and
tentacles used to maintain a steady velocity. Whilst jet propulsion
is never the sole mode of locomotion,:208 the stop-start motion
provided by the jets continues to be useful for providing bursts of
high speed – not least when capturing prey or avoiding predators.
Indeed, it makes cephalopods the fastest marine
invertebrates,:Preface and they can out-accelerate most fish.
The jet is supplemented with fin motion; in the squid, the fins flap
each time that a jet is released, amplifying the thrust; they are then
extended between jets (presumably to avoid sinking). Oxygenated
water is taken into the mantle cavity to the gills and through
muscular contraction of this cavity, the spent water is expelled
through the hyponome, created by a fold in the mantle. The size
difference between the posterior and anterior ends of this organ
control the speed of the jet the organism can produce. The
velocity of the organism can be accurately predicted for a given mass
and morphology of animal. Motion of the cephalopods is usually
backward as water is forced out anteriorly through the hyponome, but
direction can be controlled somewhat by pointing it in different
directions. Some cephalopods accompany this expulsion of water
with a gunshot-like popping noise, thought to function to frighten
away potential predators.
Cephalopods employ a similar method of propulsion despite their
increasing size (as they grow) changing the dynamics of the water in
which they find themselves. Thus their paralarvae do not extensively
use their fins (which are less efficient at low Reynolds numbers) and
primarily use their jets to propel themselves upwards, whereas large
adult cephalopods tend to swim less efficiently and with more reliance
on their fins.
Nautilus belauensis seen from the front, showing the opening of the
Early cephalopods are thought to have produced jets by drawing their
body into their shells, as
Nautilus does today.
Nautilus is also
capable of creating a jet by undulations of its funnel; this slower
flow of water is more suited to the extraction of oxygen from the
water. The jet velocity in
Nautilus is much slower than in
coleoids, but less musculature and energy is involved in its
production. Jet thrust in cephalopods is controlled primarily by
the maximum diameter of the funnel orifice (or, perhaps, the average
diameter of the funnel):440 and the diameter of the mantle
cavity. Changes in the size of the orifice are used most at
intermediate velocities. The absolute velocity achieved is limited
by the cephalopod's requirement to inhale water for expulsion; this
intake limits the maximum velocity to eight body-lengths per second, a
speed which most cephalopods can attain after two funnel-blows.
Water refills the cavity by entering not only through the orifices,
but also through the funnel.
Squid can expel up to 94% of the
fluid within their cavity in a single jet thrust. To accommodate
the rapid changes in water intake and expulsion, the orifices are
highly flexible and can change their size by a factor of twenty; the
funnel radius, conversely, changes only by a factor of around 1.5.
Some octopus species are also able to walk along the sea bed. Squids
and cuttlefish can move short distances in any direction by rippling
of a flap of muscle around the mantle.
While most cephalopods float (i.e. are neutrally buoyant or nearly so;
in fact most cephalopods are about 2–3% denser than seawater),
they achieve this in different ways. Some, such as Nautilus, allow
gas to diffuse into the gap between the mantle and the shell; others
allow purer water to ooze from their kidneys, forcing out denser salt
water from the body cavity; others, like some fish, accumulate
oils in the liver; and some octopuses have a gelatinous body with
lighter chlorine ions replacing sulfate in the body chemistry.
See also: Cirrate shell, Cuttlebone, Gladius (cephalopod), and Mollusc
Cross section of
Spirula spirula, showing the position of the shell
inside the mantle
Cuttlebone of Sepia officinalis
Nautiluses are the only extant cephalopods with a true external shell.
However, all molluscan shells are formed from the ectoderm (outer
layer of the embryo); in cuttlefish (Sepia spp.), for example, an
invagination of the ectoderm forms during the embryonic period,
resulting in a shell (cuttlebone) that is internal in the adult.
The same is true of the chitinous gladius of squid and
octopuses. Cirrate octopods have arch-shaped cartilaginous fin
supports, which are sometimes referred to as a "shell vestige" or
Incirrina have either a pair of rod-shaped stylets
or no vestige of an internal shell, and some squid also lack a
gladius. Interestingly, the shelled coleoids do not form a clade
or even a paraphyletic group. The
Spirula shell begins as an
organic structure, and is then very rapidly mineralized. Shells
that are "lost" may be lost by resorption of the calcium carbonate
Females of the octopus genus
Argonauta secrete a specialised
paper-thin eggcase in which they reside, and this is popularly
regarded as a "shell", although it is not attached to the body of the
The largest group of shelled cephalopods, the ammonites, are extinct,
but their shells are very common as fossils.
The deposition of carbonate, leading to a mineralized shell, appears
to be related to the acidity of the organic shell matrix (see Mollusc
shell); shell-forming cephalopods have an acidic matrix, whereas the
gladius of squid has a basic matrix.
Left: A giant squid found in Logy Bay, Newfoundland, in 1873. The two
long feeding tentacles are visible on the extreme left and right.
Right: Detail of the tentacular club of Abraliopsis morisi
Cephalopod limb and tentacle
Cephalopods, as the name implies, have muscular appendages extending
from their heads and surrounding their mouths. These are used in
feeding, mobility, and even reproduction. In coleoids they number
eight or ten. Decapods such as cuttlefish and squid have five pairs.
The longer two, termed tentacles, are actively involved in capturing
prey;:225 they can lengthen rapidly (in as little as 15
milliseconds:225). In giant squid they may reach a length of 8
metres. They may terminate in a broadened, sucker-coated club.:225
The shorter four pairs are termed arms, and are involved in holding
and manipulating the captured organism.:225 They too have suckers,
on the side closest to the mouth; these help to hold onto the
prey.:226 Octopods only have four pairs of sucker-coated arms, as
the name suggests, though developmental abnormalities can modify the
number of arms expressed.
The tentacle consists of a thick central nerve cord (which must be
thick to allow each sucker to be controlled independently)
surrounded by circular and radial muscles. Because the volume of the
tentacle remains constant, contracting the circular muscles decreases
the radius and permits the rapid increase in length. Typically a 70%
lengthening is achieved by decreasing the width by 23%.:227 The
shorter arms lack this capability.
The size of the tentacle is related to the size of the buccal cavity;
larger, stronger tentacles can hold prey as small bites are taken from
it; with more numerous, smaller tentacles, prey is swallowed whole, so
the mouth cavity must be larger.
Externally shelled nautilids (
Nautilus and Allonautilus) have on the
order of 90 finger-like appendages, termed tentacles, which lack
suckers but are sticky instead, and are partly retractable.
The two-part beak of the giant squid, Architeuthis sp.
All living cephalopods have a two-part beak;:7 most have a radula,
although it is reduced in most octopus and absent altogether in
Spirula.:7:110 They feed by capturing prey with their
tentacles, drawing it into their mouth and taking bites from it.
They have a mixture of toxic digestive juices, some of which are
manufactured by symbiotic algae, which they eject from their salivary
glands onto their captured prey held in their mouth. These juices
separate the flesh of their prey from the bone or shell. The
salivary gland has a small tooth at its end which can be poked into an
organism to digest it from within.
The digestive gland itself is rather short. It has four elements,
with food passing through the crop, stomach and caecum before entering
the intestine. Most digestion, as well as the absorption of nutrients,
occurs in the digestive gland, sometimes called the liver. Nutrients
and waste materials are exchanged between the gut and the digestive
gland through a pair of connections linking the gland to the junction
of the stomach and caecum. Cells in the digestive gland directly
release pigmented excretory chemicals into the lumen of the gut, which
are then bound with mucus passed through the anus as long dark
strings, ejected with the aid of exhaled water from the funnel.
Cephalopods tend to concentrate ingested heavy metals in their body
Radula § In cephalopods
Amphioctopus marginatus eating a crab
The cephalopod radula consists of multiple symmetrical rows of up to
nine teeth – thirteen in fossil classes. The organ is
reduced or even vestigial in certain octopus species and is absent in
Spirula. The teeth may be homodont (i.e. similar in form across a
row), heterodont (otherwise), or ctenodont (comb-like). Their
height, width and number of cusps is variable between species. The
pattern of teeth repeats, but each row may not be identical to the
last; in the octopus, for instance, the sequence repeats every five
Cephalopod radulae are known from fossil deposits dating back to the
Ordovician. They are usually preserved within the cephalopod's
body chamber, commonly in conjunction with the mandibles; but this
need not always be the case; many radulae are preserved in a range
of settings in the Mason Creek. Radulae are usually difficult to
detect, even when they are preserved in fossils, as the rock must
weather and crack in exactly the right fashion to expose them; for
instance, radulae have only been found in nine of the 43 ammonite
genera,[clarification needed] and they are rarer still in
non-ammonoid forms: only three pre-
Mesozoic species possess one.
Most cephalopods possess a single pair of large nephridia. Filtered
nitrogenous waste is produced in the pericardial cavity of the
branchial hearts, each of which is connected to a nephridium by a
narrow canal. The canal delivers the excreta to a bladder-like renal
sac, and also resorbs excess water from the filtrate. Several
outgrowths of the lateral vena cava project into the renal sac,
continuously inflating and deflating as the branchial hearts beat.
This action helps to pump the secreted waste into the sacs, to be
released into the mantle cavity through a pore.
Nautilus, unusually, possesses four nephridia, none of which are
connected to the pericardial cavities.
The incorporation of ammonia is important for shell formation in
terrestrial molluscs and other non-molluscan lineages. Because
protein (i.e. flesh) is a major constituent of the cephalopod diet,
large amounts of ammonium are produced as waste. The main organs
involved with the release of this excess ammonium are the gills.
The rate of release is lowest in the shelled cephalopods
Sepia as a result of their using nitrogen to fill their shells with
gas to increase buoyancy. Other cephalopods use ammonium in a
similar way, storing the ions (as ammonium chloride) to reduce their
overall density and increase buoyancy.
Reproduction and life cycle
Argonauta argo with eggcase and eggs
Detail of the hectocotylus of Ocythoe tuberculata
A dissected male specimen of Onykia ingens, showing a non-erect penis
(the white tubular structure located below most of the other organs)
A specimen of the same species exhibiting elongation of the penis to
67 cm in length
Cephalopods are a diverse group of species, but share common life
history traits, for example they have a rapid growth rate and short
life spans. Stearns (1992) suggested that in order to produce the
largest possible number of viable offspring, spawning events depend on
ecological environmental factors of the organism. The majority of
cephalopods do not provide parental care to their offspring, except
for example, octopus, which helps this organism increase the survival
rate of their offspring. Marine species life cycles are affected
by various environmental conditions. The development of a
cephalopod embryo can be greatly affected by temperature, oxygen
saturation, pollution, light intensity, and salinity. These
factors are important to the rate of embryonic development and the
success of hatching of the embryos. Food availability also plays an
important role in the reproductive cycle of cephalopods. A limitation
of food influences the timing of spawning along with their function
and growth. Spawning time and spawning vary among marine species;
it's correlated with temperature, though cephalopods in shallow water
spawn in cold months so that the offspring would hatch at warmer
temperatures. Breeding can last from several days to a month.
Cephalopods that are sexually mature and of adult size begin spawning
and reproducing. After the transfer of genetic material to the
following generation, the adult cephalopods then die. Sexual
maturation in male and female cephalopods can be observed internally
by the enlargement of gonads and accessory glands. Mating would be
a poor indicator of sexual maturation in females; they can receive
sperm when not fully reproductively mature and store them until they
are ready to fertilize the eggs. Most cephalopod males develop a
hectocotylus, an arm tip which is capable of transferring their
spermatozoa into the female mantel cavity. Though not all species use
a hectocotylus; for example, the adult nautilus releases a spadix.
An indication of sexual maturity of females is the development of
brachial photophores to attract mates.
Cephalopods are not broadcast spawners. During the process of
fertilization, the females use sperm provided by the male via external
fertilization. Internal fertilization is seen only in octopods.
The initiation of copulation begins when the male catches a female and
wraps his arm around her, either in a "male to female neck" position
or mouth to mouth position, depending on the species. The males then
initiate the process of fertilization by contracting their mantle
several times to release the spermatozoa. Cephalopods often mate
several times, which influences males to mate longer with females that
have previously, nearly tripling the amount of contractions of the
mantle. To ensure the fertilization of the eggs, female
cephalopods release a sperm-attracting peptide through the gelatinous
layers of the egg to direct the spermatozoa. Female cephalopods lay
eggs in clutches; each egg is composed of a protective coat to ensure
the safety of the developing embryo when released into the water
column. Reproductive strategies differ between cephalopod species. In
giant pacific octopus, large eggs are laid in a den; it will often
take several days to lay all of them. Once the eggs are released
and attached to a sheltered substrate the females then die. In
some species of cephalopods, egg clutches are anchored to substrates
by a mucilaginous adhesive substance. These eggs are swelled with
preivitelline fluid (PVF), a hypertonic fluid that prevents premature
hatching. Fertilized egg clusters are neutrally buoyant depending
at the depth that they were laid but can also be found in substrates
such as sand, matrix of corals, or seaweed. Because these species
do not provide parental care for their offspring, egg capsules can be
injected with ink by the female in order to camouflage the embryos
Most cephalopods engage in aggressive sex: a protein in the male
capsule sheath stimulates this behavior. They also engage in male-male
aggression, where larger males tend to win the interactions. When
a female is near, the males charge one another continuously and flail
their arms. If neither male backs away, the arms extend to the back,
exposing the mouth, followed by the biting of arm tips. During
mate competition males also participate in a technique called
flushing. This technique is used by the second male attempting to mate
with a female. Flushing removes spermatophores in the buccal cavity
that was placed there by the first mate by forcing water into the
cavity. Another behavior that males engage in is sneaker mating or
mimicry- smaller males adjust their behavior to that of a female in
order to reduce aggression. By using this technique, they are able to
fertilize the eggs while the larger male is distracted by different
male. During this process, the sneaker males quickly insert drop
like sperm into the seminal receptacle.
Mate choice is seen in cuttlefish species, where females prefer some
males over others, though characteristics of the preferred males are
unknown. A hypothesis states that females reject males by
olfactory cues rather than visual cues. Several cephalopod species
are polyandrous- accepting and storing multiple male spermatophores,
which has been identified by DNA fingerprinting. Females are no
longer receptive to mating attempts when holding their eggs in their
arm. Females can store sperm in two places (1) the buccal cavity where
recently mated males place their spermatophores, and (2) the internal
sperm-storage receptacles where sperm packages from previous males are
stored. Spermatophore storage results in sperm competition; which
states that the female controls which mate fertilizes the eggs. In
order to reduce this sort of competition, males develop agonistic
behaviors like mate guarding and flushing. Flushing is used by
both the male and female; it is the process of removing spermatophores
of other males by continuously pumping strong jets of water into the
buccal cavity of the female. This behavior however, reduces the
available time to mate with other females.
In a variety of marine organisms it is seen that females are larger in
size compared to the males in some close related species. In some
lineages, such as the blanket octopus, males become structurally
smaller and smaller resembling a term, "dwarfism" dwarf males usually
occurs at low densities. The blanket octopus male is an example of
sexual-evolutionary dwarfism; females grow 10,000 to 40,000 times
larger than the males and the sex ratio between males and females can
be distinguished right after hatching of the eggs.
Egg cases laid by a female squid
Cephalopod eggs span a large range of sizes, from 1 to 30 mm in
diameter. The fertilised ovum initially divides to produce a disc
of germinal cells at one pole, with the yolk remaining at the opposite
pole. The germinal disc grows to envelop and eventually absorb the
yolk, forming the embryo. The tentacles and arms first appear at the
hind part of the body, where the foot would be in other molluscs, and
only later migrate towards the head.
The funnel of cephalopods develops on the top of their head, whereas
the mouth develops on the opposite surface.:86 The early
embryological stages are reminiscent of ancestral gastropods and
The shells develop from the ectoderm as an organic framework which is
subsequently mineralised. In Sepia, which has an internal shell,
the ectoderm forms an invagination whose pore is sealed off before
this organic framework is deposited.
Chtenopteryx sicula paralarvae. Left: Two very young paralarvae. The
circular tentacular clubs bear approximately 20 irregularly arranged
suckers. Two chromatophores are present on each side of the mantle.
Centre: Ventral, dorsal and side views of a more advanced paralarva.
An equatorial circulet of seven large yellow-brown chromatophores is
present on the mantle. Posteriorly the expanded vanes of the gladius
are visible in the dorsal view. Right: Ventral and dorsal views of a
very advanced paralarva.
Left: Immature specimens of Chiroteuthis veranyi. In this paralarval
form, known as the doratopsis stage, the pen is longer than the mantle
and 'neck' combined
Right: A mature Chiroteuthis veranyi. This species has some of the
longest tentacles in proportion to its size of any known cephalopod.
The length of time before hatching is highly variable; smaller eggs in
warmer waters are the fastest to hatch, and newborns can emerge after
as little as a few days. Larger eggs in colder waters can develop for
over a year before hatching.
The process from spawning to hatching follows a similar trajectory in
all species, the main variable being the amount of yolk available to
the young and when it is absorbed by the embryo.
Unlike most other molluscs, cephalopods do not have a morphologically
distinct larval stage. Instead the juveniles are known as paralarvae.
They quickly learn how to hunt, using encounters with prey to refine
Growth in juveniles is usually allometric, whilst adult growth is
Main article: Evolution of cephalopods
The traditional view of cephalopod evolution holds that they evolved
Late Cambrian from a monoplacophoran-like ancestor with a
curved, tapering shell, which was closely related to the
gastropods (snails). The similarity of the early shelled
Plectronoceras to some gastropods was used in support of
this view. The development of a siphuncle would have allowed the
shells of these early forms to become gas-filled (thus buoyant) in
order to support them and keep the shells upright while the animal
crawled along the floor, and separated the true cephalopods from
putative ancestors such as Knightoconus, which lacked a siphuncle.
Neutral or positive buoyancy (i.e. the ability to float) would have
come later, followed by swimming in the
Plectronocerida and eventually
jet propulsion in more derived cephalopods.
However, some morphological evidence is difficult to reconcile with
this view, and the redescription of
Nectocaris pteryx, which did not
have a shell and appeared to possess jet propulsion in the manner of
"derived" cephalopods, complicated the question of the order in which
cephalopod features developed – provided
Nectocaris is a cephalopod
at all. Their position within the
Mollusca is currently wide open
to interpretation – see Mollusca#Phylogeny.
Early cephalopods were likely predators near the top of the food
chain. They underwent pulses of diversification during the
Ordovician period to become diverse and dominant in the Paleozoic
Mesozoic seas. In the Early Palaeozoic, their range was far
more restricted than today; they were mainly constrained to
sublittoral regions of shallow shelves of the low latitudes, and
usually occur in association with thrombolites. A more pelagic
habit was gradually adopted as the
Deep-water cephalopods, whilst rare, have been found in the Lower
Ordovician – but only in high-latitude waters. The mid
Ordovician saw the first cephalopods with septa strong enough to cope
with the pressures associated with deeper water, and could inhabit
depths greater than 100–200 m. The direction of shell
coiling would prove to be crucial to the future success of the
lineages; endogastric coiling would only permit large size to be
attained with a straight shell, whereas exogastric coiling –
initially rather rare – permitted the spirals familiar from the
fossil record to develop, with their corresponding large size and
diversity. (Endogastric mean the shell is curved so as the ventral
or lower side is longitudinally concave (belly in); exogastric means
the shell is curved so as the ventral side is longitudinally convex
(belly out) allowing the funnel to be pointed backwards beneath the
An ammonoid with the body chamber missing, showing the septal surface
(especially at right) with its undulating lobes and saddles
The ancestors of coleoids (including most modern cephalopods) and the
ancestors of the modern nautilus, had diverged by the Floian Age of
Ordovician Period, over 470 million years ago. The
Bactritida, a Silurian–
Triassic group of orthocones, are widely held
to be paraphyletic to the coleoids and ammonoids, that is, the latter
groups arose from within the Bactritida.:393 An increase in the
diversity of the coleoids and ammonoids is observed around the start
Devonian period, and corresponds with a profound increase in
fish diversity. This could represent the origin of the two derived
Unlike most modern cephalopods, most ancient varieties had protective
shells. These shells at first were conical but later developed into
curved nautiloid shapes seen in modern nautilus species. Competitive
pressure from fish is thought to have forced the shelled forms into
deeper water, which provided an evolutionary pressure towards shell
loss and gave rise to the modern coleoids, a change which led to
greater metabolic costs associated with the loss of buoyancy, but
which allowed them to recolonise shallow waters.:36 However, some
of the straight-shelled nautiloids evolved into belemnites, out of
which some evolved into squid and cuttlefish.[verification needed] The
loss of the shell may also have resulted from evolutionary pressure to
increase manoeuvrability, resulting in a more fish-like habit.:289
There has been debate on the embryological origin of cephalopod
appendages. Until the mid-twentieth century, the "Arms as Head"
hypothesis was widely recognized. In this theory, the arms and
tentacles of cephalopods look similar to the head appendages of
gastropods, suggesting that they might be homologous structures.
Cephalopod appendages surround the mouth, so logically they could be
derived from embryonic head tissues. However, the "Arms as Foot"
hypothesis, proposed by
Adolf Naef in 1928, has increasingly been
favoured; for example, fate mapping of limb buds in the chambered
nautilus indicates that limb buds originate from "foot" embryonic
The approximate consensus of extant cephalopod phylogeny, after
Strugnell et al. 2007, is shown in the cladogram. Mineralized taxa
are in bold. The attachment of the clade including Sepia and Spirula
is unclear; either of the points marked with an asterisk may represent
the root of this clade.
Basal octopods (e.g. Argonauta)
Heteroteuthis (bobtail squid)
Certain squid (e.g. Bathyteuthis)
The internal phylogeny of the cephalopods is difficult to constrain;
many molecular techniques have been adopted, but the results produced
Nautilus tends to be considered an outgroup,
Vampyroteuthis forming an outgroup to other squid; however in one
analysis the nautiloids, octopus and teuthids plot as a polytomy.
Some molecular phylogenies do not recover the mineralized coleoids
(Spirula, Sepia, and Metasepia) as a clade; however, others do recover
this more parsimonious-seeming clade, with
Spirula as a sister group
to Sepia and Metasepia in a clade that had probably diverged before
the end of the Triassic.
Molecular estimates for clade divergence vary. One 'statistically
robust' estimate has
Nautilus diverging from
415 ± 24 million years ago.
Chambered nautilus (
Common cuttlefish (Sepia officinalis)
Atlantic bobtail (Sepiola atlantica)
European squid (Loligo vulgaris)
Common octopus (
The classification presented here, for recent cephalopods, follows
largely from Current Classification of Recent Cephalopoda (May 2001),
for fossil cephalopods takes from Arkell et al. 1957, Teichert and
Moore 1964, Teichert 1988, and others. The three subclasses are
traditional, corresponding to the three orders of cephalopods
recognized by Bather.
Class Cephalopoda († indicates extinct groups)
Subclass Nautiloidea: Fundamental ectocochleate cephalopods that
provided the source for the
Ammonoidea and Coleoidea.
Order † Plectronocerida: the ancestral cephalopods from the Cambrian
Ellesmerocerida (500 to 470 Ma)
Endocerida (485 to 430 Ma)
Actinocerida (480 to 312 Ma)
Discosorida (482 to 392 Ma)
Pseudorthocerida (432 to 272 Ma)
Tarphycerida (485 to 386 Ma)
Oncocerida (478.5 to 324 Ma)
Nautilida (extant; 410.5 Ma to present)
Orthocerida (482.5 to 211.5 Ma)
Ascocerida (478 to 412 Ma)
Bactritida (418.1 to 260.5 Ma)
Subclass † Ammonoidea: Ammonites (479 to 66 Ma)
Goniatitida (388.5 to 252 Ma)
Ceratitida (254 to 200 Ma)
Ammonitida (215 to 66 Ma)
Coleoidea (410.0 Ma-Rec)
Decapodiformes (also known as Decabrachia or
† Belemnoidea: Belemnites and kin
Genus † Jeletzkya
Aulacocerida (265 to 183 Ma)
Phragmoteuthida (189.6 to 183 Ma)
Hematitida (339.4 to 318.1 Ma)
Belemnitida (339.4 to 66 Ma)
Belemnoteuthis (189.6 to 183 Ma)
?Order † Boletzkyida
Order Spirulida: Ram's horn squid
Order Sepiida: cuttlefish
Order Sepiolida: pygmy, bobtail and bottletail squid
Order Teuthida: squid
Octopodiformes (also known as Vampyropoda)
Family † Trachyteuthididae
Order Vampyromorphida: Vampire squid
Order Octopoda: octopus
Other classifications differ, primarily in how the various decapod
orders are related, and whether they should be orders or families.
Suprafamilial classification of the Treatise
This is the older classification that combines those found in parts K
and L of the Treatise on
Invertebrate Paleontology, which forms the
basis for and is retained in large part by classifications that have
Nautiloids in general (Teichert and Moore, 1964) sequence as given.
Subclass † Endoceratoidea. Not used by Flower, e.g. Flower and
Kummel 1950, interjocerids included in the Endocerida.
Order † Endocerida
Order † Intejocerida
Subclass † Actinoceratoidea Not used by Flower, ibid
Order † Actinocerida
Subclass † Nautiloidea Nautiloidea in the restricted sense.
Plectronocerida subsequently split off as
Orthocerida Includes orthocerids and pseudorthocerids
Order † Ascocerida
Order † Oncocerida
Order † Discosorida
Order † Tarphycerida
Order † Barrandeocerida A polyphyletic group now included in the
Subclass † Bactritoidea
Order † Bactritida
Ammonoidea (Miller, Furnish and Schindewolf, 1957)
Suborder † Anarcestina
Suborder † Clymeniina
Suborder † Goniatitina
Suborder † Prolecanitina
Ammonoidea (Arkel et al., 1957)
Suborder † Ceratitina
Suborder † Phylloceratina
Suborder † Lytoceratina
Suborder † Ammonitina
Subsequent revisions include the establishment of three Upper Cambrian
orders, the Plectronocerida, Protactinocerida and Yanhecerida;
separation of the pseudorthocerids as the Pseudorthocerida, and
elevating orthoceritoids as the Subclass Orthoceratoidea.
Shevyrev (2005) suggested a division into eight subclasses, mostly
comprising the more diverse and numerous fossil forms,
although this classification has been criticized as arbitrary.
Various species of ammonites
Holotype of Ostenoteuthis siroi from family Ostenoteuthidae.
A fossilised belemnite
Subclass † Ellesmeroceratoidea
Plectronocerida (501 to 490 Ma)
Order † Protactinocerida
Order † Yanhecerida
Ellesmerocerida (500 to 470 Ma)
Subclass † Endoceratoidea (485 to 430 Ma)
Endocerida (485 to 430 Ma)
Intejocerida (485 to 480 Ma)
Subclass † Actinoceratoidea
Actinocerida (480 to 312 Ma)
Subclass Nautiloidea (490.0 Ma- Rec)
Basslerocerida (490 to 480 Ma)
Tarphycerida (485 to 386 Ma)
Lituitida (485 to 480 Ma)
Discosorida (482 to 392 Ma)
Oncocerida (478.5 to 324 Ma)
Nautilida (410.5 Ma-Rec)
Orthoceratoidea (482.5 to 211.5 Ma)
Orthocerida (482.5 to 211.5 Ma)
Ascocerida (478 to 412 Ma)
Dissidocerida (479 to 457.5 Ma)
Order † Bajkalocerida
Bactritoidea (422 to 252 Ma)
Ammonoidea (410 to 66 Ma)
Coleoidea (410.0 Ma-rec)
Pyritized fossil of Vampyronassa rhodanica, a vampyromorphid from the
Callovian (166.1 million years ago)
Another recent system divides all cephalopods into two clades. One
includes nautilus and most fossil nautiloids. The other clade
Neocephalopoda or Angusteradulata) is closer to modern coleoids, and
includes belemnoids, ammonoids, and many orthocerid families. There
are also stem group cephalopods of the traditional Ellesmerocerida
that belong to neither clade.
Monophyly of coeloids
The coeloids have been thought to possibly represent a polyphyletic
group,:289 although this has not been supported by the rising body
of molecular data.
In popular culture
Main article: Cephalopods in popular culture
Cephalopods, typically octopuses and squids, have been depicted
commonly in Western pop culture as creatures that enjoy hugging or
latching onto objects with their limbs and refusing to release. Some
of the most notable uses of cephalopods in popular culture include
Cthulhu, Squidward Tentacles, and the cephalopod-like robotic arms of
A famous Japanese print
The Dream of the Fisherman's Wife
The Dream of the Fisherman's Wife depicts
close human octopus interaction
A prominent Soviet/Russian rock band
Nautilus Pompilius was named
after the chambered nautilus.
Pain in cephalopods
List of nautiloids
List of ammonites
^ a b c d e f g h i Wilbur, Karl M.; Trueman, E.R.; Clarke, M.R., eds.
(1985), The Mollusca, 11. Form and Function, New York: Academic Press,
^ "Welcome to CephBase". CephBase. Retrieved 29 January 2016.
^ a b c d Wilbur, Karl M.; Clarke, M.R.; Trueman, E.R., eds. (1985),
The Mollusca, 12. Paleontology and neontology of Cephalopods, New
York: Academic Press, ISBN 0-12-728702-7
^ Bartol, I. K.; Mann, R.; Vecchione, M. (2002). "Distribution of the
Lolliguncula brevis in Chesapeake Bay: effects of
selected abiotic factors". Marine Ecology Progress Series. 226:
^ "Are there any freshwater cephalopods?". ABC Science. 16 January
^ a b c d e f g h i j k l Nixon, Marion; Young, J. Z. (2003). The
Brains and Lives of Cephalopods. New York: Oxford University Press.
^ Tricarico, E.; Amodio, P.; Ponte, G.; Fiorito, G. (2014). "Cognition
and recognition in the cephalopod mollusc
coordinating interaction with environment and conspecifics". In
Witzany, G. Biocommunication of Animals. Springer. pp. 337–349.
^ Budelmann, B. U. (1995). "The cephalopod nervous system: What
evolution has made of the molluscan design". In Breidbach, O.; Kutsch,
W. The nervous systems of invertebrates: An evolutionary and
comparative approach. ISBN 978-3-7643-5076-5.
^ Raven, Peter et al. (2003). Biology, p. 669. McGraw-Hill
Education, New York. ISBN 9780073383071.
^ Tasaki, I.; Takenaka, T. (1963). "Resting and action potential of
squid giant axons intracellularly perfused with sodium-rich solutions"
(PDF). Proceedings of the National Academy of Sciences of the United
States of America. 50 (4): 619–626. doi:10.1073/pnas.50.4.619.
^ a b Packard, A. (1972). "Cephalopods and fish: the limits of
convergence". Biological Reviews. 47 (2): 241–307.
^ Macia, Silvia; Robinson, Michael P.; Craze, Paul; Dalton, Robert;
Thomas, James D. (2004). "New observations on airborne jet propulsion
(flight) in squid, with a review of previous reports". Journal of
Molluscan Studies. 70 (3): 297–299.
^ a b Muramatsu, K.; Yamamoto, J.; Abe, T.; Sekiguchi, K.; Hoshi, N.;
Sakurai, Y. (2013). "Oceanic squid do fly". Marine Biology. 160 (5):
^ "Scientists Unravel Mystery of Flying Squid". Ocean Views. National
Geographic. 20 February 2013.
^ Jabr, Ferris (2 August 2010). "Fact or Fiction: Can a
Squid Fly out
of Water?". Scientific American.
^ a b Serb, J. M.; Eernisse, D. J. (2008). "Charting Evolution's
Trajectory: Using Molluscan Eye Diversity to Understand Parallel and
Convergent Evolution". Evolution Education and Outreach. 1 (4):
^ Wells, Martin J. (2011). "Part M, Chapter 4: Physiology of
Coleoids". Lawrence, Kansas, USA.
ISSN 2153-4012. (subscription required)
^ a b c d e f g h i j k Boyle, Peter; Rodhouse, Paul (2004).
Cephalopods : ecology and fisheries. Blackwell.
doi:10.1002/9780470995310.ch2. ISBN 0-632-06048-4.
^ a b Messenger, John B.; Hanlon, Roger T. (1998). Cephalopod
Behaviour. Cambridge: Cambridge University Press. pp. 17–21.
^ Hanlon and Messenger, 68.
^ Mäthger, L.; Roberts, S.; Hanlon, R. (2010). "Evidence for
distributed light sensing in the skin of cuttlefish, Sepia
officinalis". Biology Letters. 6 (5): 600–603.
doi:10.1098/rsbl.2010.0223. PMC 2936158 .
^ Michinomae, M.; Masuda, H.; Seidou, M.; Kito, Y. (1994). "Structural
basis for wavelength discrimination in the banked retina of the
firefly squid Watasenia scintillans". Journal of Experimental Biology.
193 (1): 1–12. PMID 9317205.
^ Seidou, M.; Sugahara, M.; Uchiyama, H.; Hiraki, K.; Hamanaka, T.;
Michinomae, M.; Yoshihara, K.; Kito, Y. (1990). "On the three visual
pigments in the retina of the firefly squid, Watasenia scintillans".
Journal of Comparative Physiology A. 166 (6).
^ Stubbs, A. L.; Stubbs, C. W. (2015). "A novel mechanism for color
vision: Pupil shape and chromatic aberration can provide spectral
discrimination for 'color blind' organisms".
bioRxiv 017756 .
^ a b Kingston, A. C.; Kuzirian, A. M.; Hanlon, R. T.; Cronin, T. W.
(2015). "Visual phototransduction components in cephalopod
chromatophores suggest dermal photoreception". Journal of Experimental
Biology. 218 (10): 1596–1602. doi:10.1242/jeb.117945.
^ "The cephalopods can hear you". BBC News. 2009-06-15. Retrieved
^ Tong, D.; Rozas, S.; Oakley, H.; Mitchell, J.; Colley, J.;
Mcfall-Ngai, J. (Jun 2009). "Evidence for light perception in a
bioluminescent organ". Proceedings of the National Academy of Sciences
of the United States of America. 106 (24): 9836–9841.
ISSN 0027-8424. PMC 2700988 . PMID 19509343.
^ "integument (mollusks)."Encyclopædia Britannica. 2009.
Encyclopædia Britannica 2006 Ultimate Reference Suite DVD
^ Ramirez, M. D.; Oakley, T. H (2015). "Eye-independent,
light-activated chromatophore expansion (LACE) and expression of
phototransduction genes in the skin of
Octopus bimaculoides" (PDF).
Journal of Experimental Biology. 218: 1513–1520.
^ Manda, Štěpán; Turek, Vojtěch (2009). "Minute
nautiloids with unusual color patterns". Acta Palaeontologica
Polonica. 54 (3): 503–512. doi:10.4202/app.2008.0062.
^ Turek, Vojtěch (2009). "Colour patterns in Early Devonian
cephalopods from the Barrandian Area: Taphonomy and taxonomy". Acta
Palaeontologica Polonica. 54 (3): 491–502.
^ Hanlon, Roger T.; Messenger, John B. (1999).
Cambridge University Press. p. 2. ISBN 0-521-64583-2.
^ "inkfish". Merriam-Webster. Retrieved 1 February 2018.
^ Bickerdyke, John (1895). Sea Fishing. London: Longmans, Green, and
Co. p. 114. the common squid or calamary (Loligo vulgaris). It is
sometimes called the pen-and-ink fish, on account of its ink bag, and
the delicate elongated shell which is found within it.
^ Wells, M.J. (1 April 1980). "Nervous control of the heartbeat in
octopus". Journal of Experimental Biology. 85 (1): 111–28.
^ Ghiretti-Magaldi, A. (October 1992). "The Pre-history of Hemocyanin.
The Discovery of Copper in the Blood of Molluscs". Cellular and
Molecular Life Sciences. Birkhäuser Basel. 48 (10): 971–972.
^ a b c Gilbert, Daniel L.; Adelman, William J.; Arnold, John M.
Squid as Experimental Animals (illustrated ed.). Springer.
^ a b c "Electron Microscopical and Histochemical Studies of
Differentiation and Function of the
Gill (Sepia officinalis
L.)". Zoomorphologie. 93 (3): 193–207. 1979.
^ Bone, Q.; Brown, E. R.; Travers, G. (1994). "On the respiratory flow
in the cuttlefish Sepia officinalis" (PDF). Journal of Experimental
Biology. 194 (1): 153–165. PMID 9317534.
^ Cole, A.; Hall, B. (2009). "
Cartilage differentiation in cephalopod
molluscs". Zoology. 112 (1): 2–15. doi:10.1016/j.zool.2008.01.003.
^ See also http://tolweb.org/articles/?article_id=4200
^ a b c d e Wilbur, Karl M.; Clarke, M.R.; Trueman, E.R., eds. (1985),
"11: Evolution of Buoyancy and Locomotion in recent cephalopods", The
Mollusca, 12. Paleontology and neontology of Cephalopods, New York:
Academic Press, ISBN 0-12-728702-7
^ a b Anderson, E.; Demont, M. (2000). "The mechanics of locomotion in
the squid Loligo pealei: Locomotory function and unsteady
hydrodynamics of the jet and intramantle pressure". Journal of
Experimental Biology. 203 (18): 2851–2863. PMID 10952883.
^ a b c Bartol, I. K.; Krueger, P. S.; Thompson, J. T.; Stewart, W. J.
(2008). "Swimming dynamics and propulsive efficiency of squids
throughout ontogeny". Integrative and Comparative Biology. 48 (6):
720–733. doi:10.1093/icb/icn043. PMID 21669828.
^ Shea, E.; Vecchione, M. (2002). "Quantification of ontogenetic
discontinuities in three species of oegopsid squids using model II
piecewise linear regression". Marine Biology. 140 (5): 971–979.
^ Johnson, W.; Soden, P. D.; Trueman, E. R. "A study in jet
propulsion: an analysis of the motion of the squid, Loligo vulgaris".
Journal of Experimental Biology. 56 (1972): 155–165.
^ Campbell, Reece & Mitchell (1999), p. 612.
^ Guerra, A.; Martinell, X.; González, A. F.; Vecchione, M.; Gracia,
J.; Martinell, J. (2007). "A new noise detected in the ocean". Journal
of the Marine Biological Association of the United Kingdom. 87.
^ a b Wells, Martin J.; O'Dor, R. K. (July 1991). "Jet Propulsion and
the Evolution of the Cephalopods". Bulletin of Marine Science. 49 (1):
^ Chamberlain, J., Jr. (1993). "Locomotion in ancient seas: Constraint
and opportunity in cephalopod adaptive design". Geobios. 26 (Suppl.
1): 49–61. doi:10.1016/S0016-6995(06)80360-8.
^ a b c d e O'Dor, R. K. (1988). "The forces acting on swimming
squid". Journal of Experimental Biology. 137: 421–442.
^ O'Dor, R. K.; Hoar, J. A. (2000). "Does geometry limit squid
growth?". ICES Journal of Marine Science. 57: 8–14.
^ a b c d Baratte, S.; Andouche, A.; Bonnaud, L. (2007). "Engrailed in
cephalopods: a key gene related to the emergence of morphological
novelties". Development genes and evolution. 217 (5): 353–362.
doi:10.1007/s00427-007-0147-2. PMID 17394016.
^ von Boletzky, S. (2004). "'Ammonoïdes nus': un défi pour la
phylogénie des céphalopodes ?" ['Nude ammonoids': a challenge
to cephalopod phylogeny?]. Geobios. 37: 117–118.
^ Gibson, R. N.; Atkinson, R. J. A.; Gordon, J. D. M., eds. (2006).
Oceanography and Marine Biology: An Annual Review. CRC Press.
p. 288. ISBN 1420006398.
^ Aldred, R. G.; Nixon, M.; Young, J. Z. (1983). "Cirrothauma murrayi
Chun, a finned octopod". Philosophical Transactions of the Royal
Society B: Biological Sciences. 301 (1103): 1–54.
^ Fuchs, D.; Ifrim, C.; Stinnesbeck, W. (2008). "A new Palaeoctopus
(Cephalopoda: Coleoidea) from the Late
Cretaceous of Vallecillo,
north-eastern Mexico, and implications for the evolution of Octopoda".
Palaeontology. 51 (5): 1129–1139.
^ von Boletzky, Sigurd (July 1991). "The terminal spine of sepiolid
hatchlings: its development and functional morphology (Mollusca,
Cephalopoda)". Bulletin of Marine Science. 49: 107–112.
^ a b c d Strugnell, J.; Nishiguchi, M. K. (2007). "Molecular
phylogeny of coleoid cephalopods (Mollusca: Cephalopoda) inferred from
three mitochondrial and six nuclear loci: a comparison of alignment,
implied alignment and analysis methods". Journal of Molluscan Studies.
73 (4): 399–410. doi:10.1093/mollus/eym038.
^ Warnke, K.; Keupp, H. (2005). "
Spirula – a window to the embryonic
development of ammonoids? Morphological and molecular indications for
a palaeontological hypothesis". Facies. 51: 60–65.
^ Furuhashi, T.; Schwarzinger, C.; Miksik, I.; Smrz, M.; Beran, A.
(2009). "Molluscan shell evolution with review of shell calcification
hypothesis". Comparative Biochemistry and Physiology B. 154 (3):
351–371. doi:10.1016/j.cbpb.2009.07.011. PMID 19665573.
^ Dauphin, Y. (1996). "The organic matrix of coleoid cephalopod
shells: molecular weights and isoelectric properties of the soluble
matrix in relation to biomineralization processes". Marine Biology.
125 (3): 525–529. doi:10.1007/BF00353265.
^ Toll, R. B.; Binger, L. C. (1991). "Arm anomalies: Cases of
supernumerary development and bilateral agenesis of arm pairs in
Octopoda (Mollusca, Cephalopoda)". Zoomorphology. 110 (6): 313–316.
^ Anatomy of the Common Squid. 1912.
^ Nixon 1988 in Wippich, M. G. E.; Lehmann, J. (2004). "Allocrioceras
from the Cenomanian (mid-Cretaceous) of the Lebanon and its bearing on
the palaeobiological interpretation of heteromorphic ammonites".
Palaeontology. 47 (5): 1093–1107.
^ Wilbur, Karl M.; Clarke, M.R.; Trueman, E.R., eds. (1985), "5", The
Mollusca, 12. Paleontology and neontology of Cephalopods, New York:
Academic Press, ISBN 0-12-728702-7
^ C.Michael Hogan. 2011. Celtic Sea. eds. P.Saundry & C.Cleveland.
Encyclopedia of Earth. National Council for Science and the
Environment. Washington DC.
Cephalopod radula". Tree of Life web project.
^ a b c d e Nixon, M. (1995). "A nomenclature for the radula of the
Cephalopoda (Mollusca) – living and fossil". Journal of Zoology.
236: 73–81. doi:10.1111/j.1469-7998.1995.tb01785.x.
^ a b Gabbott, S. E. (1999). "Orthoconic cephalopods and associated
fauna from the late
Ordovician Soom Shale Lagerstatte, South Africa".
Palaeontology. 42: 123–148. doi:10.1111/1475-4983.00065.
^ Landman, Neil H.; Davis, Richard Arnold; Mapes, Royal H., eds.
(2007). Cephalopods present and past: new insights and fresh
perspectives. Springer. ISBN 978-1-4020-6461-6.
^ Richardson & ... (1977). Fossils of the Mason Creek.
^ Kruta, I.; Landman, N.; Rouget, I.; Cecca, F.; Tafforeau, P. (2011).
"The role of ammonites in the
Mesozoic marine food web revealed by jaw
preservation". Science. 331 (6013): 70–72.
^ a b Barnes, Robert D. (1982).
Invertebrate Zoology. Philadelphia,
PA: Holt-Saunders International. pp. 450–460.
^ Loest, R. A. (1979). "
Ammonia Volatilization and Absorption by
Terrestrial Gastropods_ a Comparison between Shelled and Shell-Less
Species". Physiological Zoology. The University of Chicago Press. 52
(4): 461–469. doi:10.2307/30155937. JSTOR 30155937.
^ a b c Boucher-Rodoni, R.; Mangold, K. (1994). "
Ammonia production in
cephalopods, physiological and evolutionary aspects". Marine and
Freshwater Behaviour and Physiology. 25: 53–60.
^ a b c d e f g h i j k Vidal, Erica A. G. Advances in Cephalopod
Science: Biology, Ecology, Cultivation and Fisheries.
^ a b c d e Rodrigues, M.; Guerra; Troncoso. "The embryonic phase and
its implication in the hatchling size and condition of Atlantic
bobtail squid Sepiola atlantica". Helgoland Marine Research. 65 (2):
^ a b c d Arkhipkin, A. I. (1992). "Reproductive system structure,
development and function in cephalopods with a new general scale for
maturity stages". Journal of Northwest Atlantic Fishery Science. 12:
^ Saunders, W. B; Spinosa, C. (1978). "Sexual dimorphism in Nautilus
from Palau". Paleobiology. 4: 349–358.
^ Young, R. B. (1975). "A Systematic Approach to Planning Occupational
Programs". Community College Review. 3: 19–25.
^ a b c Squires, Z. E; Norman, M. D; Stuart-Fox, D. (2013). "Mating
behaviour and general spawning patterns of the southern dumpling squid
Euprymna tasmanica". Journal of Molluscan Studies. 79 (3): 263–269.
^ Marthy, H. J.; Hauser, R; Scholl, A. (1976). "Natural tranquilliser
in cephalopod eggs". Nature.
^ a b Norman, M. D.; Lu, C. C. (1997). "Redescription of the southern
dumpling squid Euprymna tasmanica and a revision of the genus Euprymna
(Cephalopoda: Sepiolidae)". Journal of the Marine Biological
Association of the United Kingdom. 77 (4): 1109–1137.
^ Iwata, Y.; Ito, K.; Sakurai, Y. (2008). "Effect of low temperature
on mating behavior of squid Loligo bleekeri". Fisheries Science. 74
(6): 1345–1347. doi:10.1111/j.1444-2906.2008.01664.x.
^ a b Fairbairn, D. (2013). "Blanket Octopus: Drifting Females and
Dwarf Males". Odd couples: Extraordinary differences between the sexes
in the animal kingdom. Princeton University Press.
^ a b Shigeno, S.; Sasaki, T.; Moritaki, T.; Kasugai, T.; Vecchione,
M.; Agata, K. (Jan 2008). "Evolution of the cephalopod head complex by
assembly of multiple molluscan body parts: Evidence from Nautilus
embryonic development". Journal of Morphology. 269 (1): 1–17.
doi:10.1002/jmor.10564. PMID 17654542.
^ Gilbert, Daniel L.; Adelman, William J.; Arnold, John M. (1990).
Squid as experimental animals. New York: Plenum Press.
^ a b Von Boletzky, S. (2003). "Biology of early life stages in
cephalopod molluscs". Advances in Marine Biology. 44: 143–203.
doi:10.1016/S0065-2881(03)44003-0. ISBN 978-0-12-026144-4.
^ Moltschaniwskyj, Natalie A. (2004). "Understanding the process of
growth in cephalopods". Marine and
Freshwater Research. 55 (4):
^ Lemche, H.; Wingstrand, K. G. (1959). "The anatomy of Neopilina
galatheae Lemche, 1957 (Mollusca, Tryblidiacea)" (Link to free full
text + plates). Galathea Report. 3: 9–73.
^ Wingstrand, K. G. (1985). "On the anatomy and relationships of
Recent Monoplacophora" (Link to free full text + plates). Galathea
Report. 16: 7–94.
^ a b c Boyle, P.; Rodhouse, P. (2005). "Origin and Evolution".
Cephalopods. p. 36. doi:10.1002/9780470995310.ch3.
^ Kröger, B. R. (2007). "Some Lesser Known Features of the Ancient
Ellesmerocerida (Nautiloidea, Cephalopoda)".
Palaeontology. 50 (3): 565–572.
^ Smith, Martin R.; Caron, Jean-Bernard (2010). "Primitive soft-bodied
cephalopods from the Cambrian". Nature. 465 (7297): 427–428.
^ a b Kröger, B.; Yun-bai, Y. B. (2009). "Pulsed cephalopod
diversification during the Ordovician". Palaeogeography,
Palaeoclimatology, Palaeoecology. 273: 174–201.
^ Dzik, J. (1981). "Origin of the Cephalopoda" (PDF). Acta
Palaeontologica Polonica. 26 (2): 161–191.
^ a b c d Kröger, B. R.; Servais, T.; Zhang, Y.; Kosnik, M. (2009).
"The origin and initial rise of pelagic cephalopods in the
Ordovician". PLoS ONE. 4 (9): e7262. Bibcode:2009PLoSO...4.7262K.
doi:10.1371/journal.pone.0007262. PMC 2749442 .
^ a b Holland, C. H. (1987). "The nautiloid cephalopods: a strange
success: President's anniversary address 1986". Journal of the
Geological Society. 144: 1–15. doi:10.1144/gsjgs.144.1.0001.
^ Kröger, Björn (2006). "Early growth-stages and classification of
orthoceridan cephalopods of the Darriwillian (Middle Ordovician) of
Baltoscandia". Lethaia. 39 (2): 129–139.
^ a b Young, R. E.; Vecchione, M.; Donovan, D. T. (1998). "The
evolution of coleoid cephalopods and their present biodivesity and
ecology". South African Journal of Marine Sciences. 20 (1): 393–420.
^ a b Tanabe, K. (2008). Cephalopods – Present and Past. Tokyo:
Tokai University Press. [page needed]
^ Basil, Jennifer; Bahctinova, Irina; Kuroiwa, Kristine; Lee, Nandi;
Mims, Desiree; Preis, Michael; Soucier, Christian (2005-09-01). "The
function of the rhinophore and the tentacles of
Nautilus pompilius L.
(Cephalopoda, Nautiloidea) in orientation to odor". Marine and
Freshwater Behaviour and Physiology. 38 (3): 209–221.
^ Shigeno, Shuichi; Sasaki, Takenori; Moritaki, Takeya; Kasugai,
Takashi; Vecchione, Michael; Agata, Kiyokazu (January 2008).
"Evolution of the cephalopod head complex by assembly of multiple
molluscan body parts: Evidence from
Nautilus embryonic development".
Journal of Morphology. 269 (1): 1–17. doi:10.1002/jmor.10564.
^ Strugnell, J.; Norman, M.; Jackson, J.; Drummond, A.; Cooper, A.
(2005). "Molecular phylogeny of coleoid cephalopods (Mollusca:
Cephalopoda) using a multigene approach; the effect of data
partitioning on resolving phylogenies in a Bayesian framework".
Molecular Phylogenetics and Evolution. 37 (2): 426–441.
doi:10.1016/j.ympev.2005.03.020. PMID 15935706.
^ Strugnell, J.; Jackson, J.; Drummond, A. J.; Cooper, A. (2006).
"Divergence time estimates for major cephalopod groups: evidence from
multiple genes". Cladistics. 22: 89–96.
^ Carlini, D. B.; Reece, K. S.; Graves, J. E. (2000). "Actin gene
family evolution and the phylogeny of coleoid cephalopods (Mollusca:
Cephalopoda)". Molecular Biology and Evolution. 17 (9): 1353–1370.
doi:10.1093/oxfordjournals.molbev.a026419. PMID 10958852.
^ Bergmann, S.; Lieb, B.; Ruth, P.; Markl, J. (2006). "The hemocyanin
from a living fossil, the cephalopod
Nautilus pompilius: protein
structure, gene organization, and evolution". Journal of Molecular
Evolution. 62 (3): 362–374. doi:10.1007/s00239-005-0160-x.
^ Bather, F.A. (1888b). "Professor Blake and Shell-Growth in
Cephalopoda". Annals and Magazine of Natural History. 6. 1: 421–426.
^ Klug, C.; Schweigert, G.; Fuchs, D.; Kruta, I.; Tischlinger, H.
(2016). "Adaptations to squid-style high-speed swimming in Jurassic
belemnitids". Biology Letters. 12: 20150877.
^ Shevyrev, A. A. (2005). "The
Cephalopod Macrosystem: A Historical
Review, the Present State of Knowledge, and Unsolved Problems: 1.
Major Features and Overall Classification of
Paleontological Journal. 39 (6): 606–614. Translated from
Paleontologicheskii Zhurnal No. 6, 2005, 33–42.
^ Shevyrev, A. A. (2006). "The cephalopod macrosystem; a historical
review, the present state of knowledge, and unsolved problems; 2,
Classification of nautiloid cephalopods". Paleontological Journal. 40
(1): 46–54. doi:10.1134/S0031030106010059.
^ Kroger, B. "Peer review in the Russian 'Paleontological Journal'".
Archived from the original on 2009-08-31.
^ Bather, F.A. (1888a). "Shell-growth in Cephalopoda (Siphonopoda)".
Annals and Magazine of Natural History. 6. 1: 298–310.
^ Berthold, Thomas; Engeser, Theo (1987). "Phylogenetic analysis and
systematization of the Cephalopoda (Mollusca)". Verhandlungen
Naturwissenschaftlichen Vereins in Hamburg. 29: 187–220.
^ Engeser, Theo (1997). "
Fossil Nautiloidea Page". Archived from the
original on 2006-09-25.
^ Lindgren, A. R.; Giribet, G.; Nishiguchi, M. K. (2004). "A combined
approach to the phylogeny of Cephalopoda (Mollusca)". Cladistics. 20
(5): 454–486. doi:10.1111/j.1096-0031.2004.00032.x.
Barskov, I. S.; Boiko, M. S.; Konovalova, V. A.; Leonova, T. B.;
Nikolaeva, S. V. (2008). "Cephalopods in the marine ecosystems of the
Paleozoic". Paleontological Journal. 42 (11): 1167–1284.
doi:10.1134/S0031030108110014. A comprehensive overview of
Campbell, Neil A.; Reece, Jane B.; Mitchell, Lawrence G. (1999).
Biology, fifth edition. Menlo Park, California: Addison Wesley
Longman, Inc. ISBN 0-8053-6566-4.
Felley, J., Vecchione, M., Roper, C. F. E., Sweeney, M. &
Christensen, T., 2001–2003: Current Classification of Recent
Cephalopoda. National Museum of Natural History: Department of
Invertebrate Zoology: Cephalopods
N. Joan Abbott, Roddy Williamson, Linda Maddock. Cephalopod
Neurobiology. Oxford University Press, 1995. ISBN 0-19-854790-0
Marion Nixon & John Z. Young. The brains and lives of Cephalopods.
Oxford University Press, 2003. ISBN 0-19-852761-6
Hanlon, Roger T. & John B. Messenger.
Cambridge University Press, 1996. ISBN 0-521-42083-0
Martin Stevens & Sami Merilaita.
Animal camouflage: mechanisms and
function. Cambridge University Press, 2011. ISBN 0-521-19911-5
Rodhouse, P. G.; Nigmatullin, Ch. M. (1996). "Role as Consumers".
Philosophical Transactions of the Royal Society B: Biological
Sciences. 351 (1343): 1003–1022. doi:10.1098/rstb.1996.0090.
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