Mollusca		Coleoidea
CYRTOSOMA		Coleoidea

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Coleoidea

CYRTOSOMA |--+--SCAPHOPODA | `--CEPHALOPODA | |--NAUTILOIDEA | `--NEOCEPHALOPODA | |--Ammonoidea | `--COLEOIDEA | |--Belemnoida | | |--Aulacocerida | | `--+--Phragmoteuthida | | `--+--Belemnitida | | | |--Belemnitina | | | `--Belemnopseina | | `--Diplobelida | `--+--DECAPODIFORMES | `--VAMPYROPODA `--GASTROPODA

Unit Contents Coleoidea   Belemnitida

Page Contents Introduction   Links

Introduction

The third of the traditional subclasses of cephalopods, coleoids can more correctly be considered the second of the two great clades that developed from early Devonian bactrid ancestors, the others of course being the ammonoids.   

Coleoids are endocochleate cephalopods; that is, they have their shell on the inside of the body. The hell is frequently vestigial, and in some cases, such as the octopi, it has disappeared altogether. These diverse, intelligent, and very successful predatory animals are the invertebrate counterpart of fish, with which it is thought they may even equal in biomass, although in number of species they are fewer. About 700 species of Recent coleoids are known (with probably more, especially deep sea forms, waiting to be discovered), and there are some 2500 fossil species, although some of these would be invalid taxa.

The Coleoidea first appear with certainty in the Early Carboniferous, but only become numerous during the Mesozoic.  

A Linnean classification of the coleoids may be found here.  

Links

Links

Coleoidea - Octopods, squids, cuttlefishes and their relatives