(Van Beneden, 1861)
Description
—ÊGeneric features. General form long and slender with the cephalothorax particularly narrow anterior to the cervical groove. Abdomen long and stouter than the thorax, more than twice as long as the carapax, tapering somewhat posteriorly; sixth somite nearly twice as long as the fifth. Carapace relatively short, bluntly rounded to form a short rostrum; posterior margin slightly emerginate, leaving the whole of the eight, nearly all the seventh, and part of the sixth, thoracic somites exposed.
Antennule with slender, greatly produced peduncle; marked sexual differences, the male being midfied with large, long hirsute lobe and an extra flagellum. Antenne with the scale slender, setose all round subequal in length to the peduncle. Eyes with remarkably lengthened, tubular eyestalks.
Endopods of thoracic limbs subequal in length with no definite nails. Pleopods of the male, first, second and fifth pairs rudimentary as in the female; third pair small, biramous, with very short, 2-segmented exopod and a longer, unsegmented, simple endopod with a small setose lobe at the base; fourth pair biramous, with minute 2-segmented endopod and very long 3-segmented exopod which has the distal segment small and armed with two very long, unequal setae or flagella, of which the longer is many-segmented. Uropod with exopod half as long again as the endopod.
Telson short, lateral margins with few very small spines ending in one large spine marking the distal end of each; apex produced, rounded, armed with a dense comb-like row of regular teeth.
— Species. The general appearance of M. slabberi is long and slender, with narrow cephalothorax. Carapace relatively short, leaving the posterior two thoracic somites exposed; anterior margin slightly produced and rounded; antero-lateral angles each produced into a well-developed spine; posterior margin only slightly emarginate.
Antennular peduncle very long and slender, over 18% of the length of the body, first segment almost as long as the other two together, armed with a strong seta on the distal end of the outer margin, third segment short, dilated, bearing the usual two flagella in the female; in the male there is, in addition to an unusually large setose lobe or appendix masculina a fourth appendix which consists of a narrow, long basal portion armed distally with a single, very long slender seta.
Antennal scale long and tapering, subequal in length to antennular peduncle, setose all round, small distal suture.
Eyes mounted on extremely long eyestalks which are three-and-a-half times as long as broad, and 17 per cent. of the whole body length; cornea occupying only two-ninths of whole organ; pigment black.
Thoracic limbs 3-8 with endopods long and slender; tarsus with seven to eight subsegments; no nail. Third pleopod of the male with sympod large, endopod slender, unsegmented, armed with long plumose setae on inner margin and at apex, exopod only about half as long as endopod, two-segmented. Fourth pleopod of the male with the second segment of sympod very long; biramous, endopod minute, three-segmented, with a very small lateral lobe on the proximal segment; exopod very long, extending beyond the posterior margin of the last abdominal somite, three-segmented, first segment twice as long as endopod, second segment more than three times as long as first, third very short, armed with two very long setae, of which the inner is shorter and is furnished with a fine comb-like row of minute spinules; outer seta about three times as long as the inner, many-segmented and unarmed.
Telson short, less than half as long as the last abdominal somite.
Uropods with exopod long, narrow, slightly bowed outward distally, more than three times as long as telson, setose all round; endopod about two-thirds as long as exopod, tapering distally, armed with a single small spine on the inner margin at the distal end of the statocyst.
Colour
Transparent and colourless with practically no pigment, except for its very black eyes.
Size
Adult from 11-15 mm long.
Depth range
Hyperbenthic: 0-65 m. Mesopodopsis slabberi is usually found in the lower levels of the water but, during the breeding season, it is found in great numbers just below the surface. It flourishes most abundantly in brackish and estuarine waters. In these localities it lives in very dense swarms.
Remarks
Euryhaline. The species shows a great adaptability of surviving in varying degrees of salinity. It may occur in almost fresh water.
Mesopodopsis slabberi is a detritus feeder and also takes small animals in its food. At certain seasons of the year the species forms a very important ingredient in the food of pelagic fishes.
Distribution in the North Sea
All North Sea, shallow and estuarine waters.
World distribution
Atlantic: 41-58°N; Baltic; Mediterranean; Black Sea; estuarine, coastal, shelf.
Abundant in the estuarine waters of Europe from Scandinavia to the Black Sea; in Africa along the north east and from the west and south-west coasts. It has not been recorded from American waters.
[After Tattersall and Tattersall, 1951]