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Description of Female.
Length 4 mm.; depth ½ mm.; width 1 ¼ mm.
Antennae. First: Reaching ½ along 5th segment of antenna 2 peduncle; length 1 mm. Flagellum of 6 segments, segments longer than wide with a few short distal setae, except end segment which has distal tuft of setae; flagellum as long as peduncle 1st segment. Peduncle 1st segment stout, greatest width slightly less than ½ length, margins setose, 2 or 3 stout hooked spines on inner margin proximally, 3 or 4 stout seta-tipped spines along inferior margin; 2nd segment ⅗ length 1st, width less than ⅓ length, long setae on margins; 3rd segment slightly narrower, ½ length 2nd, a few setae distally. Second: Length 1 ¼ mm. Peduncle stout, 3rd segment slightly wider than long, 2 stout spines and several setae at inferodistal angle; 4th segment slightly more than twice length 3rd, twice its own width; setae on margins and surface, inferodistal angle produced a little to short
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boss bearing strong spine, 3 similar spines along inferior margin; 5th segment total length barely shorter than 4th, distally produced as small triangular lobe about ⅓ way along 1st flagellar segment; width less than ⅓ length, setae on margins and surface, single stout spine ⅔ along inferior margin. Flagellum shorter and stouter than in male, otherwise similar.
Mouthparts. Like C. sextonae except Mandibles: Palp in general shape similar; strong sparsely-plumose straight seta arising from one distal angle; other giving off distally narrowing second segment which is ⅓ longer, has long fine bristles on upper margin; single strong sparsely bristled seta distally at right angles to long axis of segment and in shape an inverted U.
Epimeral Plates. First and Second: Small, ovate, deeper than wide, margins with strong, mostly plumose, setae. Third: Basically subrectangular, distal angles rounded, 2 or 3 setae on ventral margin, convex posterior margin has fringe of long setae continuing along posterior margin of pleon; wider than deep.
Urosome. One or two spines more on peduncle and rami of first uropod than in male.
Localities. Lyttelton Harbour, 27/2/1913; Auckland; Kenepuru Sound, July, 1910; Chatham Islands, coll. W. R. B. Oliver, Dec., 1910; Portobello Marine Biological Station, Otago Harbour, on wharf-piles, coll. D. E. Hurley, 19/3/53; 2/8/53 (includes ovigerous female); 19/10/53.
Hypotypes. Slides C.45, male; C.46, female, Lyttelton (Chilton Collection).
Distribution. New Zealand; Woods Hole, Mass., Long Island Sound, Cape May, N.J., U.S.A.; Southern England; Rio de Janeiro, Brazil; France; Monaco; Suez Canal; Algeria; Durban, Natal, South Africa.
Remarks. Crawford (1937) gives the impression that the species which Chilton and Thomson described was C. acherusicum, and I agree that the mislabelled C. acherusicum from Holland confused Chilton. Nevertheless, I have been able to find only one specimen of C. acherusicum from New Zealand in the collection, and that one mounted. There are, on the other hand, numerous specimens of C. acutum, and Thomson's original description suggests in one detail C. acutum: “second gnathopod … dactylos four-toothed at the extremity of its lower margin.”
Evidence from the body of Chilton's paper (1921) as to the species with which he was dealing is difficult to establish because he was confusing several species in his own material. However, the figures which he gives of the second uropod suggest C. acutum, and the presence of only the one specimen of C. acherusicum in his material suggests he was more familiar with C. acutum and it was that species he was primarily describing.
Corophium acherusicum Costa, 1857. (Figs. 35–39.)
Corophium acherusicum Costa. Costa, 1857: 232.
Crawford, 1937: 617–620, fig. 2, P.
Shoemaker, 1947: 53, figs. 2a-h; 3a-f.