When a sucker attaches itself to an object, the infundibulum mainly provides adhesion while the central acetabulum is free.
Suckers are used for grasping substratum, catching prey and for locomotion. Both of these structures are thick muscles, and are covered with a chitinous cuticle to make a protective surface. Each sucker is usually circular and bowl-like and has two distinct parts: an outer shallow cavity called an infundibulum and a central hollow cavity called an acetabulum. Suckers Ĭephalopod limbs bear numerous suckers along their ventral surface as in octopus, squid and cuttlefish arms and in clusters at the ends of the tentacles (if present), as in squid and cuttlefish. The males of most cephalopods develop a specialised arm for sperm delivery, the hectocotylus.Īnatomically, cephalopod limbs function using a crosshatch of helical collagen fibres in opposition to internal muscular hydrostatic pressure. The tentacles of Decapodiformes are thought to be derived from the fourth arm pair of the ancestral coleoid, but the term arms IV is used to refer to the subsequent, ventral arm pair in modern animals (which is evolutionarily the fifth arm pair). The limbs of nautiluses, which number around 90 and lack suckers altogether, are called cirri. Barring a few exceptions, octopuses have eight arms and no tentacles, while squid and cuttlefish have eight arms (or two "legs" and six "arms") and two tentacles. Generally, arms have suckers along most of their length, as opposed to tentacles, which have suckers only near their ends. In the scientific literature, a cephalopod arm is often treated as distinct from a tentacle, though the terms are sometimes used interchangeably, often with the latter acting as an umbrella term for cephalopod limbs.
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