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 ocean The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the surfa ...

s 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 The colossal squid (''Mesonychoteuthis hamiltoni'') is a species of very large squid belonging to the family Cranchiidae, that of the cockatoo squids or glass squids. It is sometimes called the Antarctic cranch squid or giant squid (not to b ...

, 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 Fishery can mean either the enterprise of raising or harvesting fish and other aquatic life or, more commonly, the site where such enterprise takes place ( a.k.a., fishing grounds). Commercial fisheries include wild fisheries and fish farm ...

Description

The family is

characterised A phenotypic trait, simply trait, or character state is a distinct variant of a phenotypic characteristic of an organism; it may be either inherited or determined environmentally, but typically occurs as a combination of the two.Lawrence, Eleanor ...

by an enlarged mantle and short arms that bear two rows of suckers or hooks, with the third pair of

arm In human anatomy, the arm refers to the upper limb in common usage, although academically the term specifically means the upper arm between the glenohumeral joint (shoulder joint) and the elbow joint. The distal part of the upper limb between ...

s often enlarged.

Eye An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system. In higher organisms, the ey ...

morphology varies widely, ranging from large and circular to telescopic and

stalked Stalking is unwanted and/or repeated surveillance or contact by an individual or group toward another person. Stalking behaviors are interrelated to harassment and intimidation and may include following the victim in person or monitoring th ...

. 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 Organ and organs may refer to: Biology * Organ (biology), a group of tissues organized to serve a common function * Organ system, a collection of organs that function together to carry out specific functions within the body. Musical instruments ...

that is typically visible through the transparent tissues is a cigar-shaped

digestive gland The hepatopancreas, digestive gland or midgut gland is an organ of the digestive tract of arthropods and molluscs. It provides the functions which in mammals are provided separately by the liver and pancreas, including the production of digestive ...

, 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 Bioluminescence is the emission of light during a chemiluminescence reaction by living organisms. Bioluminescence occurs in multifarious organisms ranging from marine vertebrates and invertebrates, as well as in some fungi, microorganisms inc ...

and may possess

light organ A light organ is an Electronics, electronic device which automatically converts an audio signal (such as music) into rhythmic light effects. In the 1970s, light organs were a popular lighting effect used in discotheques and dance party, parties; ...

s 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 Sedentary lifestyle is a lifestyle type, in which one is physically inactive and does little or no physical movement and/or exercise. A person living a sedentary lifestyle is often sitting or lying down while engaged in an activity like soc ...

. A large, fluid-filled

coelom The coelom (or celom) is the main body cavity in many animals and is positioned inside the body to surround and contain the digestive tract and other organs. In some animals, it is lined with mesothelium. In other animals, such as molluscs, i ...

ic 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 predator Ambush predators or sit-and-wait predators are carnivorous animals that capture their prey via stealth, luring or by (typically instinctive) strategies utilizing an element of surprise. Unlike pursuit predators, who chase to capture prey u ...

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 The bathypelagic zone or bathyal zone (from Greek βαθύς (bathýs), deep) is the part of the open ocean that extends from a depth of below the ocean surface. It lies between the mesopelagic above and the abyssopelagic below. The bathypela ...

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 In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zool ...

(both established by

Georg Johann Pfeffer Georg Johann Pfeffer (1854–1931) was a German zoologist, primarily a malacologist, a scientist who studies mollusks. Pfeffer was born in Berlin. In 1887 he became curator of the , which was established in 1843 and destroyed during World War II. ...

) 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