Liljeborg, 1853
Description
Female brood pouch large, semi-oval. Head rather short and rounded frontally, convex near the antennulae. The eyes are large. Antenna with exopodite bearing seven, and endopodite bearing six, long and densely haired setae. Exopodite of leg 1 with two long setae of unequal length and with a short spine at the caudal edge [P.intermedius-app].
Endopodite of leg 1 with first segment bearing four short, and two long setae, of which the distal one is coarse and very long; both distal segments are short and bear two long setae each. [P.intermedius-f ]. Leg 4 is rudimentary, the exopodite has one seta. The post-abdomen is very short; the caudal end is of moderate length, with short hairs at the edges. The postabdominal setae are more than twice in length than the peduncle on which they are situated, the peduncle does not reach the end of the post-abdomen. Normally 2-5 embryos in the brood pouch.
Male somewhat smaller than the female; carapace sack-shaped and triangular [P.intermedius-m]. The endopodite of leg 1 with distal segment bearing a small claw. Copulatory organ with a blunt point.
Colour white to bright yellow, transparent; darkening with age.
Ecology
P. intermedius occurs in a salinity range of 3-39ä, but is mostly found at 24-35ä. In the nordic waters, the species occurs mostly at temperatures between 9 and 18°C (total range 4.8-20.6°C). Swarming in the North Sea lasts from February until November.
Size
Female 1-1.2, male 0.9 mm in length.
Depth range
Surface to 600 (2000) m.
Distribution in the North Sea
Occurs in the northern North Sea, Skagerrak, Wadden Sea; inshore waters, but seems to avoid oligohaline conditions.
World distribution
North East Atlantic, north as Iceland (65°N) and SW Norway (62°N), North Sea, Baltic Sea, Mediterranean, Black Sea. In the North Atlantic bound to the coasts or the warmer parts.
[After Flößner, 1972]