Class Cephalopoda Mollusks in which typical molluscan foot surrounds head and forms arms and tentacles mantle surrounds mantle cavity and is part of locomotory system central nervous system highly developed, forming true brain encased in cartilaginous cranium mouth contains pair of parrotlike jaws (or beak) body usually somewhat streamlined eyes highly developed, most closely resembling in acuity those of some vertebrates about 650 living species.Groups indicated by a dagger (†) are known only as fossils.
The following classification has gained considerable acceptance among modern specialists. In living forms, except for the Sepioidea, the shell is strongly degenerate or missing and the characters used consist of details of the soft parts: presence or absence of an eyelid, tentacles retractile or contractile or both, shape and size of fins, number of arms, number of sucker rows, presence or absence of teeth and hooks on arm and tentacular suckers, radular dentition, structure of funnel organ, spermatophores, details of the hectocotyles, number of gill lamellae, and the presence, patterns, and types of photophores. In fossil cephalopods, reliance is placed upon shell details (general shape, type of coiling, external sculpture, and sutures). Britannica Explains In these videos, Britannica explains a variety of topics and answers frequently asked questions.Ĭlassification Distinguishing taxonomic features.This Time in History In these videos, find out what happened this month (or any month!) in history.#WTFact Videos In #WTFact Britannica shares some of the most bizarre facts we can find.Demystified Videos In Demystified, Britannica has all the answers to your burning questions.Britannica Classics Check out these retro videos from Encyclopedia Britannica’s archives.
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