Specific Diagnosis

A relatively small, fragile shrimp with long appendages and characteristically prominent laterally-directed eye stalks.

Rostrum short, acute, projecting slightly beyond the anterior margin of the carapace and with the dorsal margin weakly convex. Supraorbital crest armed with spine; cervical groove distinct, terminating near the prominent hepatic spine. Suprabranchial groove and ridge well marked.

Eyes large, black, cornea wider than stalk, no protuberance (ocular tubercle) on the latter. Antennular peduncular segments long and relatively slender, second and third together subequal to proximal, third a little longer than second. Third maxillipeds not greatly enlarged, subequal in length to 3rd pereiopods. Only one margin of the two distal segments of the 5th pereiopods fringed with setae.

Male with petasma as shown (Figs. 4, 5); processus ventralis long and armed distally with several small clumps of spiniform projections; lobus terminalis only a little shorter, with several terminal "crochets" (retractible hooks); lobus connectens short, triangular and with anterior face armed with closely packed crochets; lobus armatus curved, long and reaching to the lobus page 11

Figs. 1–5. Sergestes arcticus.—Fig. 1, carapace, lateral view (anterior organ of Pesta represented by broken circle) ♀. Fig. 2—Anterior part cephalothorax, lateral view (setae omitted) ♀ 10 mm. Fig. 3—immature left petasma, posterior view, ♂ 8 mm. Fig. 4—Right petasma. posterior view, ♂ carapace length 12 mm. Fig. 5—As preceding, anterior view.
Figs. 6–9. Sergestes japonicus.—Fig. 6—Carapace, lateral view, ♀ Fig. 7—Anterior part cephalothorax, lateral view (setae omitted), ♀ 28 mm. Fig. 8—Left petasma, posterior view, ♂ 21 mm. Fig. 9—As preceding, anterior view.

page 12connectens, with single row of crochets along inner margin; processus uncifer long, hooked and reaching to the base of the lobus armatus, no lobus inermis present.

Female with two curved teeth medially on coxa of 3rd pereiopod.

Carapace length of New Zealand specimens up to 15 mm, males tend to be smaller than females.