True squid are molluscs 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.
The Mastigoteuthidae, also known as whip-lash squid, are a family of small deep-sea squid. Approximately 20 known species in six genera are represented, with members found in both the mesopelagic and bathypelagic zone of most oceans. Originally described by Verill in 1881, it was later lowered by Chun (1920) to a subfamily (Mastigoteuthinae) of the Chiroteuthidae. However, Roper et al. (1969) raised it back to the family level, and this has not been changed since. The taxonomy of this family is extremely unstable, and there have been at times one genus, two genera and four subgenera(Salcedo-Vargas & Okutani, 1994), two genera and several 'groups', five genera and one species with an uncertain placement, or six genera.
Bathothauma lyromma, the lyre cranch squid, is a highly modified species of glass squid from the family Cranchiidae with a distribution which encompasses most of the world's oceans from the tropics to high latitudes.
Sandalops melancholicus, the sandal-eyed squid or melancholy cranch squid, is a small species of glass squid. It is known to reach a mantle length of 11 cm. It is distributed in the tropical and subtropical oceans around the world. It is the only species in the genus Sandalops but some authorities suggest that this may be a species complex rather than a monotypic genus.
Onykia robusta, also known as the robust clubhook squid and often cited by the older name Moroteuthis robusta, is a species of squid in the family Onychoteuthidae. Reaching a mantle length of 2 m (6.6 ft), it is the largest member of its family and one of the largest of all cephalopods. The tentacular clubs are slender, containing 15–18 club hooks. Arms of the species contain 50–60 suckers, and grow to 90–100% of the mantle length. It is found primarily in the boreal to Temperate Northern Pacific.
Idioteuthis cordiformis is a species of whip-lash squid found in tropical regions of the west Pacific Ocean. The species is commonly known as the 'love-heart squid' because the species name cordiformis is Latin for 'heart shaped'. Recently, this species has been found to consume small birdbeak dogfish.
Mastigoteuthis is a genus of whip-lash squid containing at least seven valid species. Some teuthologists consider Idioteuthis synonymous with this taxon.
Echinoteuthis atlantica is a species of whip-lash squid from the family Mastigoteuthidae. It occurs in the eastern North and South Atlantic Ocean. This squid is red in colour and similar to Echinoteuthis famelica of the Pacific but differs in having a well developed protective membrane on the tentacular club which is absent on E. famelica. The presence on this membrane on Echinoteuthis glaukopis from the Indian Ocean suggests that this may be a synonym of E. atlantica, in which case glaukopis has priority.
Mastigoteuthis dentata is a species of whip-lash squid.
Mastigoteuthis grimaldii is a species of whip-lash squid.
Mastigoteuthis psychrophila is a species of whip-lash squid. It was first described by Kir Nazimovich Nesis in 1977, based on four individuals found in Antarctic waters. The largest was 143 mm long. The squid's tentacles are 15 mm in diameter, with 0.15 mm diameter club suckers. Integumental photophores are present upon the head, arms and fins. Although uncertain, it is believed to have more than two series of photophores on the arms, differing from other species in the M. agassizii group. However, this species, like the rest of the family, is badly in need of revision.
Stoloteuthis is a small genus of bobtail squid in the family Sepiolidae and the subfamily Heteroteuthidinae with one species, Stoloteuthis leucoptera, which is found in the western and eastern Atlantic Ocean, the Mediterranean Sea, the Indian Ocean, the Antarctic Ocean and the southwestern Pacific Ocean. The other species, Stoloteuthis japonica. was described in 2011 from a type specimen collected off northeastern Honshu.
Histioteuthis reversa, commonly known as the reverse jewel squid or the elongate jewel squid, is a species of cock-eyed squid, so called because the eyes are dissimilar. It occurs at moderate depths in the Atlantic Ocean and Mediterranean Sea and is also known from the Indian Ocean.
Teuthowenia megalops, sometimes known as the Atlantic cranch squid, is a species of glass squid from the subarctic and temperate waters of the northern Atlantic Ocean. They are moderately sized squid with a maximum mantle length of 40 cm (16 in). Their very large eyes are the source for the specific name megalops. Like other members of the genus Teuthowenia, they are easily recognizable by the presence of three bioluminescent organs (photophores) on their eyeballs.
Mastigotragus is a genus of whip-lash squid containing a single species, Mastigotragus pyrodes. This species was originally placed within Mastigoteuthis, but has been subsequently separated from other species in that genus due to multiple morphological characters. This genus is characterized by a lack of antitragus in the funnel-locking cartilage, larger sucker rings on the tentacles, a particular photophore morphology, and relatively large eyelid photophore. This genus is Latin for 'whip-lash goat'.
Euprymna morsei, the Mimika bobtail squid, is a species of Indo-Pacific bobtail squid from the family Sepiolidae.
Slosarczykovia is a monotypic genus of squid, its sole representative being Slosarczykovia circumantarctica. Slosarczykovia is placed in the family Brachioteuthidae.
The European flying squid is a species of squid from the continental slope and oceanic waters of the eastern Atlantic Ocean and the Mediterranean Sea. It is the type species of the genus Todarodes, the type genus of the subfamily Todarodinae of the pelagic squid family Ommastrephidae. It is a species which is targeted by some fisheries, although it is more often a bycatch.
Grimpoteuthis megaptera is a species of umbrella octopus known from five specimens, collected by Addison Emery Verrill. Between two and three of these specimens may belong to different species.
Opisthoteuthis agassizii is a lesser-known, deep-sea octopus first described in 1883 by Addison E. Verrill.
Oral view of a sucker from the middle of a lateral arm
Aboral view of a portion of the tentacular club
Various views of club suckers
Head and funnel with funnel locking apparatus
