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).
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.
Many cranchiids spend much of their life in the upper depths of the ocean in partially sunlit waters. For concealment under these conditions, they are often transparent except for the eyes and the visceral nucleus. The visceral nucleus is generally spindle-shaped and maintains a vertical orientation to minimize the shadow that it casts (Seapy and Young, 1986). The eyes, often with ventral photophores, also maintain a constant orientation not only for concealment but, as in most cephalopods, as a visual aid to assist interpretation of objects in the environment. The ability of cranchiids to maintain the digestive gland in a vertical orientation can be seen the the photographs below. Squid were photographed in a shipboard aquarium with vertical lines placed on the back of the tank. Note the vertical orientation of the visceral nucleus of this squid when its body is in two different postures.
Figure. Side views of Leachia pacifica in different attitudes. Photographs by R. Young.
Probably all species have paralarvae in near surface waters. Some paralarvae reach a large size (ca. 50-100 mm ML) before descending into deep water as juveniles. Paralarvae of most species are easily recognized as belonging to this family by their long eyestalks. This is especially pronounced in paralarval Bathothauma. Many species go through marked morphological change with growth and at maturity. These can involve changing eye shape and position, changing fin shape, increased pigmentation, development of photophores on arm tips, various modifications of arm structure and, apparently, loss of tentacles. These changes have led to many developmental stages being named as separate species or genera.
Based on slim evidence, females seem to be semelparous (terminal spawners).
Barcode of Life Data Systems (BOLD) Stats Specimen Records:80 Specimens with Sequences:67 Specimens with Barcodes:66 Species:24 Species With Barcodes:22 Public Records:20 Public Species:16 Public BINs:16
The family Cranchiidae comprises the approximately 60 species of glass squid, also known as cockatoo squid, cranchiid, cranch squid, or bathyscaphoid squid. Cranchiid squid occur in surface and midwater depths of open oceans around the world. They range in mantle length from 10 cm (3.9 in) to over 3 m (9.8 ft), in the case of the colossal squid. The common name, glass squid, derives from the transparent nature of most species. Cranchiid squid spend much of their lives in partially sunlit shallow waters, where their transparency provides camouflage. They are characterised by a swollen body and short arms, which bear two rows of suckers or hooks. The third arm pair is often enlarged. Many species are bioluminescent organisms and possess light organs on the undersides of their eyes, used to cancel their shadows. Eye morphology varies widely, ranging from large and circular to telescopic and stalked. A large, fluid-filled chamber containing ammonia solution is used to aid buoyancy. This buoyancy system is unique to the family and is the source of their common name "bathyscaphoid squid", after their resemblance to a bathyscaphe. Often the only organ that is visible through the transparent tissues is a cigar-shaped digestivegland, which is the cephalopod equivalent of a mammalianliver. This is usually held in a vertical position to reduce its silhouette and a light organ is sometimes present on the lower tip to further minimise its appearance in the water.
Like most squid, the juveniles of cranchiid squid live in surface waters, descending to deeper waters as they mature. Some species live over 2 km below sea level. The body shape of many species changes drastically between growth stages, and many young examples could be confused for different species altogether.
Cranchiid squid represent no interest to commercial fisheries.
A cranchiid squid observed during the Operation Deep Scope Expedition of 2004. The image on the right was taken with a polarising filter.