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(Müller, 1776)

Description:
? Generic features. General form long and slender. Carapace narrow, especially anteriorly, only very slightly wider than abdomen at its widest part; anterior margin rounded with more or less produced, rounded rostrum; posterior border emarginate, leaving the whole of the last, and part of the seventh, thoracic somites exposed.
Antennular peduncle long and slender
Antennal scale linear, very long and narrow; spine marking distal end of unarmed portion cut off by a distinct articulation, outer margin naked; usually ending in a spine. Antennal peduncle very short, slender, considerably shorter than antennular peduncle. A very long spine present on the outer distal corner of peduncle.
Eyes well developed, with long, cylindrical eyestalks, extending well beyond lateral margins of carapace.
Tarsus of third-eighth thoracic endopods five- to six-segmented, with transverse articulations.
Exopod of fourth pleopod of male with 6-segmented endopod, very long; armed distally with a single long seta with spirally arranged spinules ending in a knob. Uropods, inner margins of endopod armed with six to fourteen setae, not in series.
Abdomen robust, long, with a marked downward curve in the region of the second to the forth somites and an upward curve posteriorly, giving the animals a characteristic sigmoid shape in lateral view.
Telson deeply cleft and exopod of uropod setose all round.
Marsupium of two pairs of incubatory lamellae with sometimes a rudimentary pair on the sixth thoracic somite.

This species resembles Praunus neglectus so closely that it is sufficient to indicate the differences between them. It must be borne in mind that many of these differences are not apparent in specimens which have not attained full growth.

P. flexuosus.
1. Antennal scale more than 3x as long as antennular peduncle.
2. Antennal scale 7-8 times as long as broad.
3. Apex of antennual scale usually slightly shorter than the spine terminating its outer margin.
4. Tarsus of thoracic limbs 3-7 six-segmented, limb 8 five-segmented.
5. Telson cleft to 1/6th of its length. Cleft widely open.
6. Lateral margins of telson armed with 21-27 small spines.
7. Length 25-26 mm. Sexually mature at 18 mm in British waters.
8. Colour varying from almost black to colourless. Setae on antennal scale and uropods colourless.

P. neglectus.
1. Antennal scale less than three times as long as antennular peduncle.
2. Antennal scale five times as long as broad.
3. Apex of antennal scale longer than the spine terminating its outer margin.
4. Tarsus of thoracic limbs 3-7 five-segmented; limb 8 four-segmented. Claw more defined than in P. flexuosus.
5. Telson cleft to 1/5th of its length. Cleft very narrow proximally.
6. Lateral margins armed with 18-20 spines, larger and more regular than in P. flexuosus.
7. Length 20 mm. Sexually mature at 14 mm.
8. Colour usually grass green, varying from dark olive to very pale green. Setae of antennal scale and uropods violet or reddish purple. Eyes, tips of uropods, peduncle and inner ramus of antennule golden yellow.

Size:
Adult up to 26 mm long.

Habitat:
Hyperbenthic; shallow waters.

Remarks:
Praunus flexuosus is both eurythermic and euryhaline and is common in brackish waters and in tidal zones around the North Sea coasts. Often living among Zostera and Laminaria and over sandy ground. It is a definitely species and has not been recorded south of Roscoff. except for one doubtful record from the Black Sea.

Distribution in the North Sea:
All North Sea, Skagerrak, also Baltic Sea, littoral and shallow.

World distribution:
North Atlantic: 40-71°N, Baltic; coastal; euryhaline.

Praunus flexuosus