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Archerd Shell Collection > Shell Classes > Cephalopoda Family Index

Cephalopod Family Index

Nautilus_pompiliusST.jpg (23792 bytes) OrthocerasST.jpg (31428 bytes) AmmoniteB_ST.jpg (45934 bytes) Argonauta_argo.jpg (15419 bytes)

[select a shell family below, or click on picture to see its family.]


Shell pictures, select a living family below:

Argonautidae Paper Nautilus, Argonaut
Nautilidae Chambered Nautilus

Extinct Cephalopods

Ammonoidea (fossil) Ammonites
Orthocerida (fossil) Orthoceras
Belemnoida (fossil) Belemnites



Classification (Smithsonian Institution, 4 May 2001; modified) :

Subclass: Nautiloidea (Tetrabranchiata)
Order: Nautilida
Superfamily: Nautiloidea
Family: Nautilidae
Order: Orthocerida (extinct)


Subclass: Ammonoidea (ammonites, extinct)

Subclass: Coleoidea (Dibranchiata)
Order: Belemnoidea (extinct)

Order: Spirulida
Family: Spirulidae
Order: Sepiida (cuttlefish)
Family: Sepiadariidae
Family: Sepiidae
Order: Sepiolida (cuttlefish)
Family: Idiosepiidae
Family: Sepiolidae
Order: Teuthida (squids)
Suborder: Myopsina
Family: Loliginidae
Suborder: Oegopsina
Family: Onychoteuthidae
Family: Architeuthidae
Family: Ommatostrephidae
Family: Sthenoteuthidae
Order: Vampyromorphida (vampire squid)
Family: Vampyroteuthidae
Order: Octopoda
Suborder: Cirrina (finned octopus)
Family: Cirroteuthidae
Family: Stauroteuthidae
Family: Opisthoteuthidae
Suborder: Incirrina (octopus)
Family: Bolitaenidae
Family: Octopodidae (many species)
Family: Argonautidae



The class, Cephalopoda, includes the Chambered Nautilus, cuttlefish, squid, and octopus, as well as fossil ammonite and other fossil forms. It is a very diverse class, with 600 living species and more than 7500 fossil species. In the evolution of cephalopods , three common fossil groups, the Orthocerida (Orthoceras species) , Ammonoidea, and  Belemnoidea are particularly interesting. Although not forming a monophyletic line, they indicate progressive evolutionary steps from slow moving shelled forms to high-speed shell-less forms like present-day squid and octopus.

Size varies from planktonic to some as large as sixty feet; e.g., the present day squid, Architeuthis princeps , found in open ocean. However, most cephalopods are small, and they form a major component of the food web of larger fish and whales, as they have for at least the past 200 million years. Both abyssal and shallow water forms are found.

Anatomically, the tetrabranchiate body plan is seen only in the Chambered Nautilus; whereas a dibranchiate body plan is characteristic of all other living cephalopods. "Tetrabranchiate," refers to a duplication of the paired visceral organs found in the more primitive living molluscs. The Chambered Nautilus seems to be more evolutionarily primitive in other respects also, e.g., simpler eye structure, numerous undifferentiated tentacles; and, it is rather sluggishly responsive. For these reasons, it is sometimes referred to as a surviving fossil species.

Squids ("decapods") are dibranchiate. They have eight arms and two tentacles, body fins, and an internal shell vestige for muscle attachment, reminiscent of the extinct belemnites. What remains in squid, is either a small, horny plate or rod completely encased by the mantle. Paired tentacles are used for lightning-quick grasping of prey, while the other tentacles are used for holding. Cuttlefish, in comparison to squids, have a wholly calcified internal shell, which is their distinguishing characteristic. In all the dibranchiates, either an interior vestigial shell or cartilaginous collar surrounds the highly organized brain ganglia.

Octopus species also are dibranchiate. They have eight equally long arms, and no shell or internal vestige of a shell. Most have no fins (Suborder: Incirrina). The Vampyroteuthidae (Vampire "Octopus") are actually small squids, but the two small tentacles are not obvious. In the Spirulidae family, Spirula spirula is exceptional in having a coiled and partly calcareous shell, and it is otherwise similar to a squid.

Dibranchiates have exceptionally well developed sense organs, including those for discriminating touch, chemoreception (taste), equilibrium, and excellent sight. Some deep water squid can also produce stroboscopic, bioluminescent beams of light, probably used to stun or confuse prey. Numerous accounts exist of intelligent, learned behavior in octopods, both in the anecdotes of  SCUBA divers, and in documentation by time lapse photography.

Squid are most adept at swimming. They may swim either by using their fins, which are outgrowths of the mantle, or by the more energetic means of jet propulsion, like the octopus. Accounts are available of  Onychoteuthis flying out of the water by jet propulsion, becoming airborne, then gliding by means of its outspread tail fins (Morton, 1960) . Other squid notable for taking to the air are the Ommatostrephidae and Sthenoteuthidae.

Octopods are particularly expert at camouflage and hiding, although these traits are shared to a fair extent also with squid. A system of contractile cells (chromatophores) is found in the skin, each containing any one of three or four pigments. The chromatophores can be turned on or off immediately, to produce startling color changes. Accounts exist, for example, of a deep purple octopus discharging its ink sac to blot out visibility, blanching its skin, then quickly emerging behind the ink blot as a practically invisible animal.


by Dr. James B. Wood
(live cephalopods)

Bathypolypus arcticus




Other Cephalopods
Selected Species

Archerd Shell Collection > Shell Classes > Cephalopod Family Index

Updated: 2020-07-05 02:09:17 gmt
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