A squid is a mollusc with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting these criteria. Like all other cephalopods, squid have a distinct head, bilateral symmetry, and a mantle. They are mainly soft-bodied, like octopuses, but have a small internal skeleton in the form of a rod-like gladius or pen, made of chitin.
Squid
Fossil Rhomboteuthis from the Lower Callovian (c. 164 Mya, middle Jurassic) of La Voulte-sur-Rhône, France
Fossil Plesioteuthis from the Tithonian (c. 150 Mya, upper Jurassic), Solnhofen, Germany
Basic squid features (ventral aspect)
Mollusca is the second-largest phylum of invertebrate animals, after Arthropoda; members are known as molluscs or mollusks. Around 76,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 additional species. The proportion of undescribed species is very high. Many taxa remain poorly studied.
Image: Grapevinesnail 01a
Image: Octopus 2
Image: Clams on Sandy Hook beaches panoramio
Image: Tonicella lineata