(Rathke, 1843)
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; posteroir 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 more or less definte 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.
— Species. Carapace with anterior margin broadly rounded and less produced than in P. flexuosus and P. neglectus only just covering the bases of the eyestalks. A long slender spine arises from between the bases of the antennules, and can be seen from above, looking like a sharp rostrum.
Antennular peduncle only a little longer than the eyes.
Antennal scale half as long again as antennular peduncle; about four times as long as broad; apex produced beyond the spine terminating the outer margin to about two or three times the length of that spine. Antennal peduncle half as long as scale.
Eyes shorter and more robust than in either of the other two species.
First and second thoracic limbs similar to those in the other two species except that the modified spines on the dactylus of the second pair are longer and less closely set. Thoracic limbs 3-8 with tarsus four-segmented; nail well developed; eighth limb shorter and more slender than the preceding limbs.
Telson cleft to nearly one-third of its length; cleft very narrow; lateral margins armed with 15-17 strong spines.
Uropods shorter than in either of the other species with the endopod subequal in length to the telson armed along the proximal portion of the inner margin with 5 to 6 small spines which increase in size distally.
Size
Sexually mature females 12-15 mm long.
Depth range
Coastal and shallow water; hyperbenthic.
Remarks
Praunus inermis , like its North Sea congeners, is a eurythermic, euryhaline, coastal-water form, living in swarms in shallow water among Laminaria and other seaweeds close to the shore. It is rarely seen to be swimming freely, and rests for the most part on Ulva or plants. If disturbed, it quickly returns to the weed again and rests there. The species lives in swarms in the same environment as the other Praunus species, but the swarms remain separate and the individuals do not mingle.
It is certainly more abundant in the more northern waters.
Distribution in the North Sea
All North Sea, Skagerrak, off W Norway.
World distribution
Atlantic: 48-71°N; Baltic; coastal.
[After Tattersall and Tattersall, 1951]