Tethorchestia Bousfield, 1984

Wildish, David J. & Lecroy, Sara E., 2014, Mexorchestia: a new genus of talitrid amphipod (Crustacea, Amphipoda, Talitridae) from the Gulf of Mexico and Caribbean Sea, with the description of a new species and two new subspecies, Zootaxa 3856 (4), pp. 555-577 : 557

Tethorchestia Bousfield, 1984

Tethorchestia Bousfield, 1984 , pp. 204–205.

Type species. Tethorchestia antillensis Bousfield, 1984 .

Component species. T. antillensis Bousfield, 1984 ; T. karukerae Ciavatti, 1989 ; T. palaeorchestes Bousfield & Poinar, 1995 (fossil, in amber).

Diagnosis. (modified from Bousfield 1984; Bousfield and Poinar 1995; and LeCroy 2011). Eyes large, greater than one third head length; antenna 1, approximately one half length of antenna 2 peduncle, extending slightly beyond peduncle article 4; antenna 2 not sexually dimorphic, that of male slender, not incrassate, without ventral plate on peduncle article 3; upper lip without robust setae; mandible, left lacinia mobilis 4–5 dentate; maxilliped, palp 4-articulate, article 2 with well-developed medial lobe, article 4 reduced; gnathopod 1 of male subchelate, palm well-developed, transverse, longer than dactyl; carpus and propodus, posterior margin with rounded lobe covered with palmate setae; gnathopod 1 of female parachelate, palm poorly developed, shorter than dactyl; gnathopod 2 of male subchelate, basis stout, without tubercles on anterior margin, merus and carpus free, unfused, dactyl distally attenuate, extending two thirds length of propodus, without tooth on cutting edge; gnathopod 2 of female, oostegite strap-like, with 19–27 long, simple marginal setae, basis inverted pyriform, expanded proximally, anterior margin narrowing distally; peraeopods 3–7 cuspidactylate; peraeopods 5–7 without slender setae lining anterior margin of dactyl; peraeopod 7 weakly sexually dimorphic, merus and carpus of male not or very weakly incrassate, propodus of male with 5–6 tufts of long, stiff, slightly medial slender setae on anterodistal and distal margins; pleon segments 1–3 without dorsal spines; epimera 1–3 without vertical slits; pleopods 1–3 slightly reduced, peduncles slender; uropods 1–2, rami without apical spade-like robust setae; uropod 1 not sexually dimorphic, peduncle with well-developed dorsolateral robust seta distally, outer ramus slender, without marginal robust setae; uropod 2, outer ramus subequal to inner in length; uropod 3 well-developed, ramus shorter than peduncle, at least twice as long as deep, cylindrical, not laterally compressed, tapering distally, tip subacute; telson apically notched, with 3–11 robust setae per lobe, distinctly shorter than uropod 3, not extending beyond distal end of peduncle.

Remarks. Bousfield (1982) first established the use of the number of teeth in the lacinia mobilis of the left mandible as a generic level diagnostic character within the family Talitridae , defining talitrids as 4–6-dentate and dividing the family into several groups, based in part upon the dentition of the left lacinia. Later, Bousfield (1984), in his diagnosis of the genus Tethorchestia , stated that the left mandible has a 4-dentate lacinia mobilis and placed it within the 4-dentate cuspidactylate beachflea group. However, Bousfield and Poinar (1995) modified the diagnosis of the genus to indicate that the left lacinia mobilis is "basically 4-dentate". This latter statement is somewhat open to interpretation and could be said to apply to the variably 4–5-dentate condition found in both Tethorchestia and Mexorchestia n. gen. (Figs. 2, 10; Ciavatti 1989, Figs. 13, 17). In both genera, the fifth tooth ranges in development from a virtually indistinguishable bump to a distinct, reasonably well-developed tooth and this variation does not seem to be the result of sexual dimorphism or developmental changes. A single species in the Australian genus Notorchestia Serejo and Lowry 2008 ( N. australis ), also a member of the 4-dentate cuspidactylate beachflea group, has a 4–5 dentate lacinia mobilis as well, and it thus appears that there is occasionally some intraspecific variability in this character within the group. We have modified the generic diagnosis of Tethorchestia to reflect this variability in lacinia mobilis dentition in members of the genus.