Female body comparatively slender, though having the anterior division considerably fumefied and rounded oval in form. Carapace large and deep, more than twice as long as the exposed part of the trunk, and slightly vaulted above, surface perfectly smooth throughout, and only clothed with scattered small hairs; pseudorostral projection of moderate size, triangular, subrostral corners obsolete, lower edges of carapace abruptly curved in the middle, with the anterior half minutely denticulate.
Epimeral parts of the three posterior pedigerous segments comparatively small and rounded off behind. Tail (exclusive of the terminal appendages) exceeding the length of the anterior division and very slender. Superior antennae rather elongated, the peduncle extending far beyond the tip of the pseudorostral projection, its last joint scarcely shorter than the first, but much narrower, and, like the second, clothed on both edges with slender bristles. First pair of legs exceedingly slender and elongated, and, when fully extended, exceeding half the length of the body, basal joint occupying scarcely more than 1/3 of the length of the leg, and without any spinules, penultimate joint of extraordinary length, fully equalling that of the three preceding joints combined, last joint comparatively short, not attaining even 1/3 of the length of the penultimate one; second pair likewise rather slender and much curved, basal joint comparatively short, last joint very slender, exceeding the length of the antepenultimate one; third and fourth pairs rather narrow, with the rudimentary exopodite easily observable and carrying a single apical bristle.
Uropods much elongated, with the inner ramus very narrow, and exceeding the outer by its last joint, first joint longer than the other two combined, spinules of the inner edge only five in number (three on the first, and one on each of the last two joints), apical spine very slender, almost setiform.
Telson not attaining even the length of the last caudal segment, and rather thick at the base, distal part abruptly narrowed and, as in the other species, provided with only a single pair of lateral spinules near the tip, apical spines somewhat larger, and extended straight behind.
Adult male scarcely more slender than the female, but having the carapace less deep, and the pseudorostral projection more prominent. Tail scarcely exceeding in length the anterior division, and very narrow, unarmed, terminal appendages scarcely different from those in the female.
This form was first described as a species of the genus Diastylis, the specific name proposed being derived from the unusually prolonged first pair of legs. It may be regarded as the type of the present genus, and also in other respects is easily recognisable from the three other Norwegian species. Was found in the Oslofjord and some other places on the south and west coasts of Norway, as far north as the Lofoten Islands.
Length up to 5.5 mm.
Muddy bottoms. Shelf to bathyal.
Down from 60 to 200 m.
Distribution in the North Sea
Northern North Sea, Skagerrak.
N Atlantic and Arctic Oceans.
[After Jones, 1976]