(Montagu, 1804)
Description:
Head with a large, anteriorly directed spine dorsally. Maximum length 25 mm in male and 20 mm in female.
Antenna 1 about two-thirds of the length of the body, flagellum of 18-26 articles. Flagellum of antenna 2 with 2 articles; peduncle and flagellum with short setae, widely spaced.
Pereion segment 1 with a similar spine; segment 2 with two spines in the middle and one spine on the posterior margin. Pereion segment 3 with a small triangular tubercle dorsal to the insertion of the pereiopod and two small rounded dorsal tubercles mid-way along the segment. Small rounded dorsal tubercle, or occasionally a spine, at junction of pereion segments 3 and 4; tubercles on segment 4 as on segment 3; segment 5 with a small lateral triangular tubercle one-third length along each side.
Pereiopods 3 and 4 minute, two-segmented, with a long terminal seta. Pereiopods 5, 6 and 7, six-segmented, about equal in length. Gnathopod 2 inserted one-third to one-half length along segment; basis with a downwardly directed spine on the distal anterior edge.
Gills ovoid, on segments 3 and 4 only.
Abdomen with two pairs of non-jointed appendages in male, without appendages in female. Brood pouch of female with an anterior pair of lamellae entirely setose, posterior pair setose only on the posterior half.
Habitat:
Usually sublittoral, often on algae and large hydroids.
Distribution:
All British coasts, probably more common in the south.