The Bathyteuthoidea are small,

mesopelagic The mesopelagic zone (Greek μέσον, middle), also known as the middle pelagic or twilight zone, is the part of the pelagic zone that lies between the photic epipelagic and the aphotic bathypelagic zones. It is defined by light, and begins at ...

to bathypelagic squid that in some ways resemble myopsid squid, such as ''

Loligo ''Loligo'' is a genus of squid and one of the most representative and widely distributed groups of myopsid squid. The genus was first described by Jean Baptiste Lamarck in 1798. However, the name had been used earlier than Lamarck (Schneider, ...

'' and in others the pelagic oegopsid squid. Its two families, the

Bathyteuthidae ''Bathyteuthis'' is the singular genus of squid in the family Bathyteuthidae, encompassing three species. ''Bathyteuthis'' species are found scattered throughout the world’s oceans at mesopelagic to bathypelagic depths, commonly between 700 ...

and Chtenopterygidae, each containing a single genus, have previously been included with the oegopsids. As with the oegopsids, the Bathyteuthoidea lack corneal membranes covering their eyes, something common to myopsid squid, and have paired oviducts, lacking in myopsids. As with the myopsids, bathyteuthoids have tentacle pockets in the head and small suckers on the buccal supports, found only in this group,

Loliginidae Loliginidae, commonly known as pencil squids, is an aquatic family of squid classified in the order Myopsida. Taxonomy The family Loliginidae was formerly classified in the order Teuthida. Taxonomic list The classification below follows ...

, and

Sepiidae Sepiidae is a family of cephalopods in the order Sepiida. Classification *Order Sepiida: cuttlefish **Family Sepiadariidae **Family Sepiidae ***Genus ''Metasepia'' ****''Metasepia pfefferi'', flamboyant cuttlefish ****'' Metasepia tullbergi' ...

; neither is found in true oegopsids. The Bathyteuthoidea do share the open ocean pelagic habitat with the oegopsid squid, uniting them in that way with that diverse group. The Bathyteuthidae and Chtenopterygidae differ in body conformation, the internal shell, and in the manner in which buccal supports attach to the lowermost arms (pair IV). Buccal supports attach to the

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage * Dorsal c ...

side of arms IV in the Bathyteuthidae and the

ventral Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

side of arms IV in the Chtenopterygidae.

References

Tree of Life web project: Bathyteuthoidea
{{Taxonbar, from=Q4869214 Squid