Tristenium Serov & Wilson 1995

Tristenium n.gen. Figs 1C,D, 3B

Type species. Tristenium acutirostrum (Miiller, 1991b).

Species included. See Table 1.

Etymology. Tristenium is a re-arrangement and modification of Stenetrium, and is similar to the name of the second author's son. The gender is neuter.

Diagnosis. Head frontal margin with weak lateral and antennal spines, antennal spines rounded and longer than blunt lateral spines. Eyes with circlet of few ocelli. Rostrum with broad base and narrow pointed tip. Antennular flagellum with 3 articles. Antennal article 1 without lateral spine. Maxilliped endopodite distal margin with 3 fan setae. Lateral margins of pereonites rounded; pereonites 1-4 subequal in length, longer than remaining pereonites; most pereonites with only 1 coxal lobe or spine visible in dorsal view. Male pereopod I with broad, robust propodus with denticulate setae and broad blunt teeth on propodal palm; dactylus equal in length to propodal palm; propodal palm terminal seta with small accessory seta and serrate ventral margin. Pleopod 11 protopod distal tip rounded without distal extension; exopod and endopod positioned subapically on medial margin. Appendix masculina elongate, tapering to needle-like stylet with long setae on lateral margin. Pleotelson elongate, with 3 free reduced pleonites; posterolateral spines reduced; postanal region roundly triangular, without posterolateral extensions.

Figs lE,F, 3C

Remarks. The species of this genus all possess heads with reduced lateral and antennal spines, eyes with few ocelli, narrow triangular rostrums, and appendices masculinae with long needle-like stylets. Although a stylet similar to Stenetrium adrianae occurs in this genus, the long setae on the stylet tip and the differences in the body shape, cephalon shape and the shape of the remaining pleopods clearly distinguish this genus as a separate unit.