(G.O. Sars, 1863)
Description
— Generic features. General form slender and delicate. Eyes well developed, short, reniform and flattened dorso-ventrally, pigment brilliant red in living specimens. Antennal scale with outer margin entire or coarsely serrate, without setae, terminating in a strong spine beyond, no distal suture. Last four pairs of pleopods of the male well developed and biramous, first pair with endopod reduced to a single segment. Uropod, exopod and endopod undivided, setose alle round; no spines on outer margin of exopod; inner margin of endopod may be minutely serrated. Telson very short, entire, trapeziform, lateral margins naked; apex truncate, armed with 2 pairs of strong spines; no median plumose setae.
— Species. General form smaller and more robust than in the other North Sea species of the genus. Cephalothorax slightly broader than the abdomen.
Carapace produced anteriorly between the eyes into a short obtuse point.
Antennal scale about four times as long as broad, outer margin entire, terminating in a spine beyond which the apex projects; two to three small spines on outer margin of second segment of sympod.
Eyes short and thick, greatly enlarged distally, stalk less tapering proximally than in E. erythrophthalma; very flattened dorso-ventrally; cornea reniform and occupying about one-third of the whole eye in dorsal view; pigment vermilion, deeper in colour than in E. serrata and E. abyssorum. There is a conspicuous chalk-white line between the stalk and cornea, then a regular close row of brilliant red facets followed by another white line and another close row of facets. In living specimens these two white lines are very conspicuous.
First thoracic limb small; inner margin of merus slightly expanded; dactylus conical, bearing a welldeveloped nail. Second thoracic limb very small, subequal in length to the first, but more slender; merus only slightly bowed; dactylus tapering and armed with four peculiar, strong, ciliated bristles on one side and three on the other and terminating in a slender nail which is not surrounded by the usual dense brush of setae. Third to the eighth thoracic limbs shorter than in the other species here described, eighth endopod extending to the posterior margin of the fourth abdominal somite; carpus subequal in length to the propodus which is subdivided into two subequal parts; nail very delicate.
Telson lateral margins slightly arcuate, posterior margin straight, terminal spines of female subequal in length; of the male the outer pair usually shorter than the inner; median plumose setae unusually.
Uropods with endopod in the female only slightly shorter than exopod, but in the male it is much shorter and more slender than exopod; inner margin of endopod possesses a very fine row of serrulations showing through the bases of the setae, which are often very obscure and difficult to detect; statocyst unusually large.
Colour
Transparent with scattered bright orange-red spots. In the male there is one large yellowish spot on the anterior margin of the sympod of each pleopod and another on either side of the ventral surface of each abdominal somite immediately under each pleopod as it lies stretched backward. Both sexes possess a reddish pigment area on the basis of the fourth, fifth, and sixth, thoracic limbs respectively but none on that of the seventh or eighth; a lateral yellowish spot on either side of the last thoracic, and on each abdominal, somite and some rosy pigment spots around the mouth. On the ventral surface of the sympod of each antenna there is a clear yellow spot. On the dorsal surface there is a clear yellow line, with two dots just anterior to it, at the articulation between the thorax and abdomen. The colour of the eyes is very striking, the eyestalks are pale yellow and the bright red facets of the cornea stand out against a dead white background. The yellow pigment spots on the ventral surface of the body are paler in this species than in the other British species of the genus. The embryos are a very bright red and show through the colourless transparent walls of the marsupial lamellae making them appear pink.
Size
Adult up to 6 mm long. This is one of the smallest of the mysids and sexually mature specimens have been recorded measuring only 5 mm.
Depth range
Surface to 50 m. This species is known from shallower water than any of the other species of Erythrops in the North Sea.
Remarks
E. elegans can be distinguished by its small size and relatively more robust form; the small first and second thoracic limbs; the relative shortness of the endopods of the other thoracic limbs; the sexual difference in the length of the spines of the telson and by the serrulation under the setae on the inner margin of the endopod of the uropod, though this last character is often very obscure.
Distribution in the North Sea
North Sea, Skagerrak, W Norway, eastern North Sea, littoral.
World distribution
North Atlantic: 41 - 65°N. Baltic, Mediterranean; coastal to shelf.
[After Tattersall and Tattersall, 1951]