''Histioteuthis heteropsis'' (''H. heteropsis''), also known as the strawberry squid, is a species of small cock-eyed squid. The scientific nomenclature of these squid stems from their set of differently sized eyes, one being small and blue and the other being large and yellow. It is thought that the large eye is used to see objects against dim light, while the smaller eye is more able to view bioluminescent light sources. The squid’s vernacular name arose due to its rich red skin pigmentation and the presence of

photophores A photophore is a glandular organ that appears as luminous spots on various marine animals, including fish and cephalopods. The organ can be simple, or as complex as the human eye; equipped with lenses, shutters, color filters and reflectors, ...

along its body, making it appear like a strawberry with seeds. ''H. heteropsis'' live in the ocean’s

mesopelagic zone The mesopelagic zone (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, and begins ...

and are found in the

California Current The California Current is a cold water Pacific Ocean current that moves southward along the western coast of North America, beginning off southern British Columbia and ending off southern Baja California Sur. It is considered an Eastern bound ...

and the

Humboldt Current The Humboldt Current, also called the Peru Current, is a cold, low- salinity ocean current that flows north along the western coast of South America.Montecino, Vivian, and Carina B. Lange. "The Humboldt Current System: Ecosystem components and pr ...

. Little is known about their specific feeding and mating behaviors, although their inking patterns have been subject to study. They are not easily disturbed, and only ink when provoked. ''H. heteropsis'' was discovered by Berry in 1913 and exhibited publicly for the first time at the

Monterey Bay Aquarium Monterey Bay Aquarium is a nonprofit public aquarium in Monterey, California. Known for its regional focus on the marine habitats of Monterey Bay, it was the first to exhibit a living kelp forest when it opened in October 1984. Its biologists ...

on June 27, 2014.

Description

Members of the species ''H. heteropsis'' are small squids, with mature males averaging 54-89 mm in length, and have a purplish red skin pigment.

Eyes

The eyes of ''H. heteropsis'' are dimorphic both in size and in lens pigmentation for specialized vision in the ocean’s

(200-1000 meters below the ocean surface). The different properties of the squid’s eyes allow it to see a variety of different light sources present in its habitat, primarily downwelling sunlight and bioluminescence. ''H. heteropsis'' hatchlings are born with identical eyes of the same size and pigmentation. As they develop, the left eye becomes larger and more pigmented. By adulthood, the left eye can grow to be over twice the size of the right eye and has a distinct yellow lens pigmentation. In a 2017 study conducted by Kate Thomas, Bruce Robinson, and Sönke Johnsen, it was found that the large left yellow eye is oriented upwards for viewing objects in dim sunlight and the smaller right blue eye is oriented downwards for viewing bioluminescence. While the larger eye can detect bioluminescence fairly well, the smaller eye struggles to view black objects in dim light.

Photophores

Small

, which are glandular, light-producing organs, are found in high concentrations along the entire body of ''H. heteropsis''. The photophores are more dense near the anterior head region of the squid and become smaller and farther apart near the posterior end. Apart from ''H. meleagroteuthis'', ''H. heteropsis'' is the only member in the family

Histioteuthidae Histioteuthidae is a family of Oegopsid squid. The family was previously considered to be monotypic but the World Register of Marine Species assigns two genera to this family. The species classified under Histioteuthidae are mostly weakly musc ...

to display such small and highly concentrated photophores. ''H. heteropsis'' mainly uses its photophores for two purposes:

counter-illumination Counter-illumination is a method of active camouflage seen in marine animals such as firefly squid and midshipman fish, and in military prototypes, producing light to match their backgrounds in both brightness and wavelength. Marine animals of ...

and concealing prey. In counter-illumination, the squid produces blue light from its photophores so that, when viewed from above, it blends in with the downwelling sunlight and effectively erases its silhouette. This type of

bioluminescence Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some b ...

is characterized by consistent light production, in contrast to bioluminescence used for concealing prey, which is characterized by short bursts of intense light or “flashes.” Although the exact purpose for this particular use of bioluminescence is unknown, the heavily pigmented oral cavity and interbrachial membrane of ''H. heteropsis'' and some other squids suggests that luminescence by the prey threatens the predator in some way.

Reproductive Organs

''H. heteropsis'' males do not possess a

hectocotylus A hectocotylus (plural: ''hectocotyli'') is one of the arms of male cephalopods that is specialized to store and transfer spermatophores to the female. Structurally, hectocotyli are muscular hydrostats. Depending on the species, the male may use i ...

as is common in other mesopelagic squid species, although they do have a penis which is used to transfer spermatophores to the female during copulation. During maturation, the penis grows until it can extend out of the mantle cavity. The spermatophores of ''H. heteropsis'' have short sperm masses and are stored in a looped Needham’s sac. Female ''H. heteropsis'' squids have a singular ovary where the oocytes are developed. Although not much is known about female reproductive systems in ''H. heteropsis'' specifically, other members of the family

show significant oocyte resorption (oosorption) during maturation.

Habitat

''H. heteropsis'' is generally found at ocean depths of 200-1000 meters (0.12-0.62 miles), which is considered part of the ocean’s

mesopelagic The mesopelagic zone (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, and begins ...

, or twilight, zone. The species undergoes diurnal vertical migration, where they are found at lower depths during the day and migrate up the water column at night. In a study about vertical distributions of pelagic cephalopods conducted by Clyde Roper and Richard Young, it was found that, during the day, most ''H. heteropsis'' specimens were found at 500-700 meters while at night, most were found at 300-400 meters. ''H. heteropsis'' live in the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean (or, depending on definition, to Antarctica) in the south, and is bounded by the continen ...

and are predominantly found in the

and the

. Population distribution of ''H. heteropsis'' is better known in the California Current than it is in the Humboldt Current and the species does not inhabit waters close to the equator. There is no evidence to suggest horizontal migration in histioteuthid squids, including ''H. heteropsis''. Within marine food webs, ''H. heteropsis'' plays an important role in the diets of

tuna A tuna is a saltwater fish that belongs to the tribe Thunnini, a subgrouping of the Scombridae (mackerel) family. The Thunnini comprise 15 species across five genera, the sizes of which vary greatly, ranging from the bullet tuna (max length: ...

porpoises Porpoises are a group of fully aquatic marine mammals, all of which are classified under the family Phocoenidae, parvorder Odontoceti (toothed whales). Although similar in appearance to dolphins, they are more closely related to narwhals an ...

, blue sharks,

sperm whales The sperm whale or cachalot (''Physeter macrocephalus'') is the largest of the toothed whales and the largest toothed predator. It is the only living member of the Genus (biology), genus ''Physeter'' and one of three extant species in the s ...

elephant seals Elephant seals are very large, oceangoing earless seals in the genus ''Mirounga''. Both species, the northern elephant seal (''M. angustirostris'') and the southern elephant seal (''M. leonina''), were hunted to the brink of extinction for oil ...

, and

albatross Albatrosses, of the biological family Diomedeidae, are large seabirds related to the procellariids, storm petrels, and diving petrels in the order Procellariiformes (the tubenoses). They range widely in the Southern Ocean and the North Pacifi ...

. Not much is known about the diet of ''H. heteropsis'' itself, although limited stomach content evaluations show that they feed on fish, crustaceans, and smaller squids.

Behavior

Feeding

''H. heteropsis'' searches for prey using visual clues and strikes forward at the prey using their tentacles. The tentacles then bring the prey within range of the arms, which hold the prey in place with suckers. ''H. heteropsis'', like most squids, bite immediately into the fleshy parts of the prey with their beak and release the leftover corpse.

Mating

Very little is known about mating and courtship in ''H. heteropsis'', although it is likely that these behaviors occur in deeper waters.

Spawning Spawn is the eggs and sperm released or deposited into water by aquatic animals. As a verb, ''to spawn'' refers to the process of releasing the eggs and sperm, and the act of both sexes is called spawning. Most aquatic animals, except for aquati ...

may occur in deep-midwater or near-surface waters, but it is still unclear.

Inking

Inking developed as an important protective mechanism for coleoid cephalopods after losing their ancestral external shell. However, inking is metabolically costly since it requires the discharge of both melanin and mucus. Because of this, ''H. heteropsis'' typically only inks when approached closely or touched. Researchers Stephanie Bush and Bruce Robinson observed that ''H. heteropsis'' most often produces an ink cloud categorized as “pseudomorphs,” which are “dense blobs of ink the approximate shape and size of the individual releasing them.” In all instances of inking, ''H. heteropsis'' specimens lingered in the ink cloud unless further provoked.

Taxonomy

In 1913, Berry discovered ''H. heteropsis'' and recognized it as a member of the family

due to its large number of photophores. Based on significant morphological traits, it appears that ''H. heteropsis'' is most closely related to ''H. meleagroteuthis'' and ''H. bonnellii''.

Conservation Status

Based on a 2010 assessment by the International Union for Conservation of Nature (IUCN), ''H. heteropsis'' is categorized as least concern due to its large geographic distribution. There are no known threats to the species and population information is not available. The IUCN recommends that more research be done into ''H. heteropsis'' to determine details about its population and ecological role.

References

External links

Squid Molluscs described in 1913 Taxa named by Samuel Stillman Berry {{squid-stub