''Histioteuthis reversa'', commonly known as the reverse jewel squid or the elongate jewel squid, is a species of
cock-eyed squid, so called because the eyes are dissimilar. It occurs at moderate depths in the Atlantic Ocean and Mediterranean Sea and is also known from the Indian Ocean.
Description
''Histioteuthis reversa'' grows to a
mantle length of about . The head bears four pairs of robust arms, a pair of tentacles and two unequal-sized eyes and the main body mass is enclosed in the mantle. The arms are less than one and a half times the length of the mantle. The outer arms are not joined to each other by a web and the inner arms are connected by a vestigial web remnant. The suckers on the arms are globular, usually with teeth on the margin, and the suckers on the terminal portion of the tentacles are in five or six rows, with larger suckers in the central rows. The mantle is cup-shaped and elongates considerably in females when they mature. The fins are a third to a half the length of the mantle and roughly half its width. The ventral (under) surface of the mantle has a complex arrangement of large and small compound light-emitting
photophore
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, ...
s, and seventeen large and one small photophore surround the right eye. In front of the left eye there are seven large photophores and the eye is ringed by ten to fourteen small ones.
Distribution
''Histioteuthis reversa'' is native to the Atlantic Ocean and the Mediterranean Sea. It is mostly found in the northern hemisphere but also occurs off the coast of Namibia and South Africa. The northern limit of its range is the
Newfoundland and the seas south of Iceland at 52° North. It does not occur in the Gulf of Mexico and is uncommon in the Caribbean Sea. It has been recorded in the southern Indian Ocean. It is found in the
upper waters of the open sea,
often at depths of between ,
[ and frequently in the vicinity of seamounts and other undersea features, perhaps because ]primary production
In ecology, primary production is the synthesis of organic compounds from atmospheric or aqueous carbon dioxide. It principally occurs through the process of photosynthesis, which uses light as its source of energy, but it also occurs through ...
is greater in these areas.[
]
Ecology
Little is known of the behaviour and ecology of this squid but it seems to breed over the continental slope as juveniles in the size range have been found there. Adults are eaten by various cetaceans including sperm whales (''Physeter macrocephalus''), pygmy sperm whale
The pygmy sperm whale (''Kogia breviceps'') is one of two extant species in the family Kogiidae in the sperm whale superfamily. They are not often sighted at sea, and most of what is known about them comes from the examination of stranded speci ...
s (''Kogia breviceps'')[ and ]Risso's dolphin
Risso's dolphin (''Grampus griseus'') is a dolphin, the only species of the genus ''Grampus''. Some of the closest related species to these dolphins include: pilot whales (''Globicephala'' spp.), pygmy killer whales (''Feresa attenuata''), melon ...
(''Grampus griseus''), a fact confirmed by examining the stomach contents of stranded animals among which the indigestible beaks
The beak, bill, or rostrum is an external anatomical structure found mostly in birds, but also in turtles, non-avian dinosaurs and a few mammals. A beak is used for eating, preening, manipulating objects, killing prey, fighting, probing for food, ...
of the squids are found.Gladius
''Gladius'' () is a Latin word meaning "sword" (of any type), but in its narrow sense it refers to the sword of ancient Roman foot soldiers. Early ancient Roman swords were similar to those of the Greeks, called '' xiphe'' (plural; singular ''xi ...
File:Reversa1.jpg, Clockwise from top: lateral, ventral and dorsal views
References
External links
{{Taxonbar, from=Q2471939
Squid
Molluscs described in 1880
Marine molluscs of Europe
Cephalopods of Europe
Taxa named by Addison Emery Verrill