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| Cranchiidae | |
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| Cranchiid squid juvenile found inAntarctica | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Cephalopoda |
| Order: | Oegopsida |
| Superfamily: | Cranchioidea |
| Family: | Cranchiidae Prosch, 1847[1] |
| Subfamilies | |
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| Synonyms | |
ThefamilyCranchiidae comprises the approximately 60 species ofglass squid, also known ascockatoo squid,bathyscaphoid squid,cranch squid, or simplycranchiids.[2] Thecommon name "glass squid" derives from thetransparent bodies of most species. Cranchiid squid occur in surface and midwater depths ofopen oceans around the world. Cranchiid squid spend much of their lives in partially sunlit shallow waters, where their transparency providescamouflage.[dubious –discuss]
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.[citation needed] The family ranges inmantle length from 10 cm (3.9 in) to over 3 m (9.8 ft), in the case of thecolossal squid, which is thelargest invertebrate alive.[3]
Thetype genus of the family,Cranchia, is named for English naturalistJohn Cranch.[4][5] Cranchiid squid are of no interest to commercialfisheries.[citation needed]
The family ischaracterised by an enlarged mantle and short arms that bear two rows ofsuckers or hooks, with the third pair ofarms often enlarged.Eye morphology varies widely, ranging from large and circular to telescopic andstalked. A large, fluid-filledcoelomic cavity containingammonia solution is used to aidbuoyancy.[6][7] This buoyancy system is unique to the family and is the source of their common name "bathyscaphoid squid", after their resemblance to abathyscaphe. The onlyorgan that is typically visible through the transparent tissues is a cigar-shapeddigestive gland, a cephalopod analogue of theliver; this organ is usually held in a vertical position to reduce itssilhouette. Many species arebioluminescent and may possesslight organs on the lower tip of their digestive gland and on the undersides of their eyes, used tocancel their shadows and evade predators.[8][9][additional citation(s) needed] Cranchiids have lower activity levels and metabolic rates than other families of squid, being moresedentary.[10][7]
Cranchiids occupy a variety oftrophic levels, with some species relying heavily onmesopelagiccrustaceans such ascopepods and small fishes; cranchiids as a whole may prey on a broad variety of species.[10] Recent research usingfatty acid andstable isotope analyses has shown that smaller cranchiids in theBenguela Upwelling System feed at mid to lower trophic levels, whereas larger, more muscular squid such asTodarodes andAbraliopsis occupy higher trophic positions; theecological niche of cranchiids has even been compared to those of planktonicsiphonophores.[10] Early juveniles may also exploit productive surface waters for faster growth before transitioning to deeper zones.[11] Because of their lower activity levels, the family is thought to compriseambush predators.[7]
As they develop, glass squids often exhibit a two-phase life cycle:juveniles in theepipelagic layers, then migrating intobathypelagic waters as adults.[11][additional citation(s) needed] By remaining translucent and harnessing specialized buoyancy mechanisms involving ammonia retention, cranchiids reduce energy expenditure and adapt to low-light deep-sea habitats[12]. This vertical migration strategy is thought to minimize predation risk while maximizing feeding opportunities.[citation needed]
The family contains twosubfamilies (both established byGeorg Johann Pfeffer) and about 15 genera:[13]
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