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(G.O. Sars, 1866)

Description
?Generic features. The Genus Leptomysis is easily distinguished from most other genera by the form of the evenly rounded apex of the telson with no trace of an apical cleft. The large number of spines arming the lateral margins of the telson are arranged in groups of smaller spines between larger ones.
Eyes well developed, almost globular, with strong, triangular eyestalks and extending well beyond the lateral margins of the body.
Pleopods of the female rudimentary, in the form of slender unjointed, setose plates; those of the male well developed, biramous and natatory. Second and third segments of endopod of first thoracic limbs separate and distinct. Uropod long and slender, with very long narrow exopod without suture. Endopod of uropod with spines on inner margin only.
Marsupium consisting of three pairs of incubatory lamellae.
?Species. Carapace produced anteriorly into a more or less acutely pointed, triangular rostrum; posterior margin emarginate. L. lingvura may be distinguished from Leptomysis mediterranea and Leptomysis gracilis, by the following characters.
General form: the species is much shorter, more compact and robust than either of the other two. Integument smooth and the whole animal less transparent.
Rostrum short, extending to less than half the length of the first segment of the antennular peduncle; triangular, acutely pointed; no notches on margin above the eyestalks. The form of the rostrum is the most reliable character by which the species may be recognised.
Antennal scale shorter than in L. mediterranea, being less than twice the length of the antennular peduncle; distal segment occupies one-fourth to one-third of the total length and has from four to five setae on each margin.
Eyes more closely set than in the other two species with only the cornea projecting beyond the lateral margins of the carapace; eyestalks less contracted at the base than in L. gracilis.
Thoracic limbs with basal segment of the exopod of the thoracic limbs much larger and stouter than in either of the other species. Basis of the sympod of the pleopods more robust and broader than in either of the other two species.
Telson shorter and considerably broader than in either of the other two species; shorter than the last abdominal somite; apex broadly rounded, normally armed with two long spines flanking two much smaller median spinules; no constrictions marking the insertion of the distal large spines on lateral margins; apical long spines usually separated from the most distal large spines of the lateral margin by three or four spinules.
Uropods shorter and broader than in either of the other species; the spines arming the inner margin of the endopod are similarly graduated to those of L. mediterranea and extend over a similar distance but they are very much more crowded in the region of the statocyst, which is much larger than in that species and more nearly as in L. gracilis.

Colour:
The branching brown pigment system that is a marked feature of L. mediterranea, is absent in L. lingvura. The animal is of a pale rosy colour with less yellow tinging than in L. gracilis and the body has a milky opaque appearance. Less transparent than either of the other two species; diffusely coloured with a rosy pigment which may be slightly yellowish especially on the last abdominal somite and along the telson. There is a branching pigment spot of a darker colour on the ventral side of each abdominal somite and the marsupium is well provided with dark brown pigment spots.

Size:
Adult up to 17 mm long.

Habitat:
Littoral; usually found in swarms near the coast in water of 10 metres in depth.

Remarks:
This species closely resembles Leptomysis mediterranea and Leptomysis gracilis.
All three species carry out to some extent the same kind of migratory movements as taken on several occasions in townets at the surface at night. Living in such comparatively shallow water, it has time during the hours of darkness to reach the surface. Nearly all the day-time records are either from pools between tide marks or from the bottom in water of not more than 50 m.

Distribution in the North Sea:
All North Sea, littoral.

World distribution:
Atlantic 44-63°N; Mediterranean; coastal, shelf.

Leptomysis lingvura