Coleoidea

Coleoidea

Coleoidea (pronounced: /koʊliːˈɔɪdiə/) is a subclass within the class Cephalopoda of the phylum Mollusca. The term is derived from the Greek words "koleos" meaning sheath and "eidos" meaning form, referring to the internal shell of these creatures.

Definition

Coleoidea is a group of marine animals that includes squids, octopuses, and cuttlefish. Unlike other cephalopods, they have a soft body and an internal shell, or in some cases, no shell at all.

Anatomy

The anatomy of Coleoidea is characterized by a well-developed head, large eyes, and tentacles. The body is divided into a head, a visceral mass, and a foot. The foot has evolved into a complex set of tentacles and highly developed sensory organs.

Evolution

The Coleoidea subclass evolved during the Devonian period, around 400 million years ago. They are believed to have evolved from the subclass Nautiloidea, which had a prominent external shell.

Classification

The subclass Coleoidea is further divided into three orders: Octopoda (octopuses), Decapodiformes (squids and cuttlefish), and the extinct order Belemnoidea (belemnites).

Habitat and Distribution

Coleoidea species are found in all the world's oceans, from the Arctic and Antarctic regions to the tropics. They inhabit a wide range of depths, from the shoreline to the abyssal depths.

Related Terms

• Cephalopoda: The class to which Coleoidea belongs.
• Octopoda: An order within the subclass Coleoidea.
• Decapodiformes: Another order within the subclass Coleoidea.
• Belemnoidea: An extinct order within the subclass Coleoidea.
• Nautiloidea: The subclass from which Coleoidea is believed to have evolved.

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