decapodiform

Decapodiformes, or decapodiforms, is a clade within the subclass Coleoidea of the class Cephalopoda. The term refers to cephalopods commonly known as squids and cuttlefish and their close relatives. Decapodiforms are contrasted with octopodiforms, which include octopuses and related cephalopods that generally have eight arms and lack the paired long feeding tentacles characteristic of decapodiforms.

Morphology and key features

Decapodiforms are typically characterized by ten limbs: eight arms and two longer feeding tentacles. The arms bear suckers, while the tentacles usually extend and retract with a club at the distal end used to seize prey. Most decapodiforms have a streamlined body adapted for jet propulsion and often possess a pair of fins for steering. Internal supports vary among groups; cuttlefish retain an internalized cuttlebone, while many squids possess a rigid pen or gladius. Coloration and body patterning are commonly controlled by chromatophores, enabling camouflage and signaling.

Taxonomy and diversity

Extant decapodiforms include several major groups: squids (order Teuthida) and cuttlefish (order Sepiida). A smaller group, Spirulida, includes the ram’s horn squid. The decapodiform lineage also has a rich fossil record, with modern forms diversifying in the Cenozoic after earlier radiations in the Mesozoic. This contrasts with octopodiforms, which generally occupy a different evolutionary branch and display eight arms without long feeding tentacles.

Ecology and life history

Decapodiforms inhabit marine environments worldwide, from coastal to deep-sea habitats. They are primarily predatory, using rapid movement and tentacular strikes to capture prey such as crustaceans, fish, and other mollusks. Many species produce ink as a defense and have relatively short lifespans, with reproductive cycles culminating in semelparity in several groups.