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P.E. Müller, 1868

Description
Female egg-shaped in lateral view; brood pouch with a large, marked spine (mucro) [E.spinifera-f]. Antennulae clearly separated from the lower side of the head, lower distal side almost perpendicularly curved upwards. Legs rather short, the first leg not elongated. The exopodite of leg 1 long and narrow with two long distal setae. The endopodite of leg 1 consists of three segments, the first segment long, with four setae; the second and third segments with one or two long curved setae respectively. Distal segment of endopodites of legs 2 and 3 with four setae. Exopodite of leg 3 with two setae [E.spinifera-app ]. Leg 4 very short, not well segmented, with four small distal bristles; the exopodite bears one seta. Caudal peduncle [cp] well developed (longer than in E. nordmanni). Brood pouch with 6-7 parthogenetic eggs.
Male carapace narrowing and pointed strongly in lateral view, however, without marked spine [E.spinifera-m]. Last segment of endopodite of leg 1 with a small hook [E.spinifera-app ].
Colour bright grey to bright yellow, opaque.

Ecology
Evadne spinifera is a thermophilic, somewhat euryhaline oceanic species; preferring warmer waters, and is most abundant between 14 and 18°C. Temperature range 3-28°C; salinity range 5.51-37ä. Swarming occurs in the North Sea from about May to September.

Size
Female 0.9-1.35 mm; male ca. 1.1 mm (including distal spine of carapace).

Depth range
Surface to 2000 m.

Distribution in the North Sea
Northern North Sea, might occur in the southern North Sea, Wadden Sea, Skagerrak, also in the Kattegat; absent from the Baltic Sea except for the most western part.

World distribution
World-wide, absent from (sub)polar waters. Regarding the NE Atlantic: from Faeroer to Mediterranean, also Black Sea.

[After Flößner, 1972]

Evadne spinifera