The

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Cranchiidae comprises the approximately 60 species of glass squid, also known as cockatoo squid, bathyscaphoid squid, cranch squid, or simply cranchiids. The

common name In biology, a common name of a taxon or organism (also known as a vernacular name, English name, colloquial name, country name, popular name, or farmer's name) is a name that is based on the normal language of everyday life; and is often con ...

"glass squid" derives from the transparent bodies of most species. Cranchiid squid occur in surface and midwater depths of open oceans around the world. Cranchiid squid spend much of their lives in partially sunlit shallow waters, where their transparency provides

camouflage Camouflage is the use of any combination of materials, coloration, or illumination for concealment, either by making animals or objects hard to see, or by disguising them as something else. Examples include the leopard's spotted coat, the b ...

. 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. The family ranges in mantle length from to over , in the case of the colossal squid, which is the largest invertebrate alive. The

type genus In biological taxonomy, the type genus (''genus typica'') is the genus which defines a biological family and the root of the family name. Zoological nomenclature According to the International Code of Zoological Nomenclature, "The name-bearin ...

of the family, '' Cranchia'', is named for English naturalist John Cranch. Cranchiid squid are of no interest to commercial fisheries.

Description

The family is characterised by an enlarged mantle and short arms that bear two rows of suckers or hooks, with the third pair of arms often enlarged. Eye morphology varies widely, ranging from large and circular to telescopic and stalked. Recent studies have revealed that certain cranchiid squids, such as ''Galiteuthis glacialis'', possess photophores—light-producing organs—on their eyes. These photophores emit bioluminescence that matches the intensity of downwelling sunlight, effectively masking the squid's silhouette from predators below. This counter-illumination strategy is a sophisticated form of camouflage in the mesopelagic zone. The photophores consist of laminated, fiber-like cells with semi-coaxial protein-dense layers surrounding axial cytoplasm, enabling precise control over light emission. The only organ that is typically visible through the transparent tissues is a cigar-shaped digestive gland, a cephalopod analogue of the

liver The liver is a major metabolic organ (anatomy), organ exclusively found in vertebrates, which performs many essential biological Function (biology), functions such as detoxification of the organism, and the Protein biosynthesis, synthesis of var ...

; this organ is usually held in a vertical position to reduce its

silhouette A silhouette (, ) is the image of a person, animal, object or scene represented as a solid shape of a single colour, usually black, with its edges matching the outline of the subject. The interior of a silhouette is featureless, and the silhouett ...

. Many species are bioluminescent and may possess light organs on the lower tip of their digestive gland and on the undersides of their eyes, used to cancel their shadows and evade predators. Cranchiids have lower activity levels and metabolic rates than other families of squid, being more sedentary. A large, fluid-filled coelomic cavity containing

ammonia Ammonia is an inorganic chemical compound of nitrogen and hydrogen with the chemical formula, formula . A Binary compounds of hydrogen, stable binary hydride and the simplest pnictogen hydride, ammonia is a colourless gas with a distinctive pu ...

solution is used to aid

buoyancy Buoyancy (), or upthrust, is the force exerted by a fluid opposing the weight of a partially or fully immersed object (which may be also be a parcel of fluid). In a column of fluid, pressure increases with depth as a result of the weight of t ...

. This buoyancy system is unique to the family and is the source of their common name "bathyscaphoid squid", after their resemblance to a

bathyscaphe A bathyscaphe () is a free-diving, self-propelled deep-sea submersible, consisting of a crew cabin similar to a '' Bathysphere'', but suspended below a float rather than from a surface cable, as in the classic ''Bathysphere'' design. The floa ...

. This system appears to develop further as cranchiids mature and move from surface waters to bathypelagic zones. By consolidating ammonia in one compartment, they minimize energy costs associated with staying neutrally buoyant. Observations suggest that juveniles maintain lower ammonium levels in the sac, possibly reflecting foraging in shallower habitats, whereas adults exhibit higher concentrations for stable flotation in deeper depths.

Diet

Cranchiids occupy a variety of

trophic level The trophic level of an organism is the position it occupies in a food web. Within a food web, a food chain is a succession of organisms that eat other organisms and may, in turn, be eaten themselves. The trophic level of an organism is the ...

s, with some species relying heavily on

mesopelagic The mesopelagic zone (Greek language, 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 ...

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s such as

copepod Copepods (; meaning 'oar-feet') are a group of small crustaceans found in nearly every freshwater and saltwater habitat (ecology), habitat. Some species are planktonic (living in the water column), some are benthos, benthic (living on the sedimen ...

s and small fishes; cranchiids as a whole may prey on a broad variety of species. Recent research using

fatty acid In chemistry, in particular in biochemistry, a fatty acid is a carboxylic acid with an aliphatic chain, which is either saturated and unsaturated compounds#Organic chemistry, saturated or unsaturated. Most naturally occurring fatty acids have an ...

and stable isotope analyses has shown that smaller cranchiids in the Benguela Upwelling System feed at mid to lower trophic levels, whereas larger, more muscular squid such as ''

Todarodes ''Todarodes'' is a genus of flying squid from the subfamily Todarodinae, of which it is the type genus. The genus contains five species which are partially allopatric but between them their distributions encompass most of the world's oceans an ...

'' and '' Abraliopsis'' occupy higher trophic positions; the

ecological niche In ecology, a niche is the match of a species to a specific environmental condition. Three variants of ecological niche are described by It describes how an organism or population responds to the distribution of Resource (biology), resources an ...

of cranchiids has even been compared to those of planktonic

siphonophore Siphonophorae (from Ancient Greek σίφων (siphōn), meaning "tube" and -φόρος (-phóros), meaning "bearing") is an order within Hydrozoa, a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine ...

s. Early juveniles may also exploit productive surface waters for faster growth before transitioning to deeper zones. Because of their lower activity levels, the family is thought to comprise ambush predators.

Migration

As they develop, glass squids often exhibit a two-phase life cycle: juveniles in the

epipelagic The photic zone (or euphotic zone, epipelagic zone, or sunlight zone) is the uppermost layer of a body of water that receives sunlight, allowing phytoplankton to perform photosynthesis. It undergoes a series of physical, chemical, and biological ...

layers, then migrating into bathypelagic waters as adults. By remaining translucent and harnessing specialized buoyancy mechanisms involving ammonia retention, cranchiids reduce energy expenditure and adapt to low-light deep-sea habitats. This vertical migration strategy is thought to minimize predation risk while maximizing feeding opportunities.

Reproduction

In terms of reproduction, ''Galiteuthis glacialis'' (one such example of Cranchiidae) exhibits unique strategies adapted to the deep-sea environment. Spawning occurs in the bathypelagic zone, where females release eggs in a single batch—a process known as synchronous ovulation. Post-spawning, females undergo tissue degeneration, leading to increased buoyancy and causing them to ascend toward the surface. This phenomenon may explain the higher capture rates of mature females compared to males, which are hypothesized to die and sink to the seafloor after mating.

Genera

The family contains two subfamilies (both established by Georg Johann Pfeffer) and about 15 genera: *Subfamily Cranchiinae **Genus '' Cranchia'' **Genus '' Leachia'' **Genus '' Liocranchia'' *Subfamily Taoniinae **Genus '' Bathothauma'' **Genus '' Belonella'' **Genus '' Egea'' **Genus '' Galiteuthis'' **Genus '' Helicocranchia'' **Genus '' Liguriella'' **Genus '' Megalocranchia'' **Genus '' Mesonychoteuthis'' **Genus '' Sandalops'' **Genus '' Taonius'' **Genus '' Teuthowenia'' *'' Parateuthis tunicata'' (''

incertae sedis or is a term used for a taxonomy (biology), taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertainty ...

'')

References

External links

{{Authority control Cranchioidea