Leuckart, 1859
Description
Female with an almost spherical brood pouch, more or less perpendicular in respect to the body. Carapace faintly reticulate. Head round. Eyes very large, occupying almost the whole forehead. Lower edge of labrum rounded. The antennulae [a1] [P.polyphemoides-f] are very small and unable to move; they are situated on a common protuberance and are fused partially with this protuberance and the lower side of the head; the antennulae [a] bear at the end four sensory papillae. Exopodite of antenna with seven setae; the distal segment of both antennal branches are very small [P.polyphemoides-app ]. Exopodite of legs 1-3 with three long setae that are unequal in length; exopodite of leg 4 with two setae. Distal segment of endopodite of leg 1 with two, very large setae, about the same length as the whole leg. The postabdomen is very short with short end. The postabdominal setae are short but still much longer than the very small reduced caudal peduncle on which they are situated. Brood pouch with 2-7 embryos.
Male with small conical carapace. Head and eyes larger than in the female. Distal segment of endopodite of leg 1 situated on a small peduncle, bearing a long hook; the preceding segment with only one seta [P.polyphemoides-app]. The copulatory organ is rounded off distally.
Colour grey to yellowish white, transparent; the postabdominal end is often bluish.
Ecology
Neritic, eurytherm and euryhaline species from eutrophic waters. Occurring at salinities ranging from 1.05 to 35.1 ä and tolerates temperatures up to 21°C (Baltic Sea) or 27°C (Black Sea). Rarely occurring in fresh water.
Size
Female 0.6-0.65 mm; male 0.4-0.55 mm.
Depth range
Surface.
Distribution in the North Sea
Northern North Sea, Skagerrak, Wadden Sea, also Baltic Sea.
World distribution
NE Atlantic: all European coasts from Lofoten (Norway) to Black Sea and Sea of Asov. Also in Caspian Sea by migration through the Volga-Don Canal. NW Atlantic: American East coast. South Atlantic: Argentinean East coast and West and South coasts of South Africa. Pacific: New Zealand coasts.
[After Flößner, 1972]