Cranchiids are small (Helicocranchia: ca. 100 mm mantle length [ML]) to large (Mesonychoteuthis: ca. 2000 mm ML) squids that possess a large buoyancy chamber and, hence, the common name "bathyscaphoid squid." In general appearance they often appear to have bloated bodies and short arms. The mantle is generally thin but muscular. Several species have been observed in deep water from submersibles to exhibit a peculiar posture (cockatoo posture) with the arms and tentacles folded back over the head (Vecchione and Roper, 1991). Cranchiid paralarvae are common in near-surface waters and many remain in this habitat until reaching a rather large size (ca. 50-100 mm ML). Most species occupy progressively deeper waters as they grow larger (ontogenetic descent). This is one of the more speciose families of squids with about 60 species, many of which are undescribed (Voss, et al., 1992).

Diagnosis

An oegopsid ...

• with head fused to mantle at three points (ie, at funnel and nuchal locking-apparatuses).
• with coelom modified into a large buoyancy chamber.