Latatheres, Ahyong, 2018

Ahyong, Shane T., 2018, Revision of Ostracotheres H. Milne Edwards, 1853 (Crustacea: Brachyura: Pinnotheridae), Raffles Bulletin of Zoology 66, pp. 538-571 : 563-564

Latatheres new genus

Diagnosis. Female: Carapace transversely ovate to roundedsubquadrate, wider than long; weakly sclerotised, soft, thin; longitudinally vaulted; front transverse in dorsal view, not produced; anterolateral margins undefined; dorsal surface smooth, regions undefined. Eyes small, scarcely visible in dorsal view. Antennal flagellum not reaching dorsal margin of orbit. Maxilliped 3 ischiomerus completely fused, without trace of suture; palp 2-segmented; carpus shorter than propodus; propodus spatuliform, gently tapering distally; exopod flagellum 1-segmented, distally setose. Chelipeds equal, stout, robust, dactylus and pollex with simple, pointed tips. Pereopods 2–5 symmetrical from left to right, subcylindrical; dactyli with sharp simple apices, pereopod 3 dactylus longer than pereopod 4–5 dactyli. Pereopod 5 articulating with body at or above level of pereopod 4. Abdomen with 6 free somites and telson; in adults, widest at somites 4 and 5, covering bases of walking legs. Gonopore simple, ovate, on sternite 5 near mesial end of sternite 5/6 suture. Male: unknown.

Type species. Ostracotheres tomentipes Takeda & Konishi, 1994 , by present designation.

Etymology. An arbitrary combination of of the Latin, latus, broad, and the suffix - theres, alluding to proportionally wide carapace of species of the genus. Gender: masculine.

Composition. Latatheres affinis (H. Milne Edwards, 1853) new combination, L. tomentipes ( Takeda & Konishi, 1994) new combination.

Remarks. Latatheres is unique among pinnotherid genera with a 2-segmented maxilliped 3 palp in the transversely ovate-subrectangular carapace (rather than subcircular to polygonal and about as long as wide). Of the genera revised herein, Latatheres is perhaps nearer to Discorsotheres than to either Austrotheres or Ostracotheres , sharing subcylindrical walking legs and a 1-segmented maxilliped 3 exopod flagellum. Apart from carapace form, however, Latatheres differs from Discorsotheres in numerous features including the setose versus glabrous carapace and the left–right symmetrical walking legs with moderately curved dactyli (versus pereopod 3 asymmetrical and strongly curved dactyli). The maxilliped 3 of Latatheres approaches that of Gemmotheres Campos, 1996 (from bivalve molluscs) and Tunicotheres Campos, 1996 (from ascidians) in the tapering propodus and absence of the inner angle on the ischiomerus. One species of Latatheres , L. affinis , has pereopod 5 articulating dorsad to pereopod 4 as in Tunicotheres , but these genera are otherwise dissimilar. Latatheres shows few obvious similarities to other pinnotherid genera, although the slender maxilliped 3 ischiomerus, with the rounded distomesial margin extending distally beyond the palp articulation resembles that of the monotypic Epulotheres Manning, 1993a (host Brachidontes modiolus [ Linnaeus, 1767]), and Nannotheres Manning & Felder, 1996 (host Malleus candeanus [d’Orbigny, 1853]), both from the Caribbean Sea. Species of each of these genera also have a thin, membranous carapace, albeit subcircular ( Nannotheres ) or subhexagonal ( Epulotheres ), rather than transversely ovate-subrectangular as in Latatheres . Other features of the maxilliped 3 palp, however, distinguish the three genera: the propodus of the palp is shorter than the carpus in Nannotheres , and in Epulotheres , the palp is 3-segmented. Unfortunately, males of Latatheres , Epulotheres and Nannotheres are presently unknown.

One species each of Latatheres is known from the Indian and Pacific oceans ( Fig. 13 ). Both species mature at less than 9 mm carapace width; the hosts for neither species are known.

Figures

Fig. 13. Distribution of species of Latatheres new genus. (●) L. affinis (H. Milne Edwards, 1853) new combination; (■) L. tomentipes (Takeda & Konishi, 1994) new combination.