Myanmarorchestia Hou

Hou, Zhonge & Zhao, Shuangyan, 2017, A new terrestrial talitrid genus, Myanmarorchestia, with two new species from Myanmar (Crustacea, Amphipoda, Talitridae), ZooKeys 705, pp. 15-39 : 16-17

Genus Myanmarorchestia Hou gen. n.

Type species.

Myanmarorchestia peterjaegeri Hou, sp. n.

Etymology.

The generic name is derived from “Myanmar” in combination with the Orchestia stem.

Diagnosis.

Body size medium. Eyes rounded or sub-rounded, approximately 1/3 of head length. Antenna I reaching mid-point of peduncular article V of antenna II, flagellum a little shorter than peduncle. Antenna II 28% of body length, flagellum a little longer than peduncle. Mandible left lacinia mobilis 4-dentate. Maxilliped palp with four articles, first two articles broad; article III not lobate distomedially, article IV distinct, short, with apical spine and setae.

Gnathopod I coxal plate with anterior process prominent, carpus lacking pellucid lobe, propodus simple, narrowed distally in both sexes. Gnathopod II sexually dimorphic; propodus of male transitional form, weakly chelate, with tumescence, propodus of female mitten-shaped. Pereopods simplidactylate, with two spines at hinge of unguis. Coxal gills present on gnathopod II and pereopods III–VI; each gill lobed and convoluted, one or two lobes with ridged margins or filamentous projections. Oostegites slender, present on gnathopod II and pereopods III–V.

Epimeral plates acuminate posterodistally, ventral margins without armature, lacking submarginal pits. Pleopods well-developed, peduncles with plumose setae on exterior margins. Uropod I peduncle with large distolateral spine, outer ramus marginally bare. Uropod III ramus shorter than peduncle. Telson subtriangular shaped, apically notched, each lobe with one or two apical spines.

Remarks.

Myanmarorchestia Hou, gen. n. is quite unique in having complex coxal gills which bears filamentous projections, simple gnathopod I in both sexes, and weakly chelate, transitional gnathopod II in male.

The new genus belongs to the Orchestia group. It is most similar to the genus Bousfieldia Chou & Lee, 1996 in left lacinia 4-dentate, well-developed pleopods and bare outer ramus in uropod I. It can be distinguished from Bousfieldia by the following characters ( Bousfieldia in parentheses): gnathopod II in male subtriangle, with tumescence (strongly subchelate, oval in shape); pereopods simplidactylate (cuspidactylate); coxal gills of gnathopod II and pereopods III–VI lobed and convoluted, with ridged margins or filamentous projections (coxal gills lobed at middle, no filamentous projections).

The new genus can be distinguished from other terrestrial Orchestia groups from Indo-West Pacific margins ( Lanorchestia Miyamoto & Morino, 2010, Mizuhorchestia Morino, 2014 and Nipponorchestia Morino & Miyamoto, 2015) by gnathopod II subtriangle (oval); pereopods simplidactylate (cuspidactylate); and pleopods well-developed (reduced).

This new genus shows morphological similarities to one landhopper genus from the Philippines, Curiotalitrus Lowry & Coleman, 2012 in sharing antenna I shorter than peduncular article V of antenna II; mandible left lacinia mobilis 4-dentate; article IV of maxilliped palp very short, well defined; uropod III ramus shorter than peduncle. It can be distinguished from Curiotalitrus by the following characters ( Curiotalitrus in parentheses): gnathopod I carpus slightly expended near distal end, propodus stout (subchelate; posterior margins of carpus and propodus with palmate lobes); gnathopod II sexually dimorphic, propodus of male subtriangle, with tumescence (not sexually dimorphic, mitten-shaped); pleopods rami with numerous articles (fused 1-articulate); uropod I of male similar to that of the female (sexual dimorphism in uropod I); telson with 1-2 apical spines on each lobe (with 3-6 robust setae).

The new genus Myanmarorchestia is similar to landhopper genera Arcitalitrus Hurley, 1975, Keratroides Hurley, 1975 and Mysticotalitrus Hurley, 1975 in sharing following characters: left mandible lacinia mobilis 4-dentate; maxilliped palp article II unlobed, article IV distinct and small; gnathopod I simple; pereopods III–VII simplidactylate; and uropod I peduncle with distinct distolateral spine, outer ramus marginally bare. However, genera Arcitalitrus , Keratroides and Mysticotalitrus with more or less reduced pleopods, the peduncle lacking plumose setae; and telson not subtriangular in shape. Solitroides female is also similar to that of the new genus, but coxal gills not lobed, reduced pleopod III are distinguishing characters. The genus Talitriator Methuen, 1913 shares most features with the new genus, but gnathopod II in male is mitten-shaped and the telson is wider in middle. The peculiar gnathopod II in male of the new genus Myanmarorchestia is also exhibited in Puhuruhuru patersoni (Stephensen, 1938), Parorchestia lesliensis (Hurley, 1957), and Platorchestia zachsi (Derzhavin, 1937), but they can be distinguished from the new genus by cuspidactylate pereopods III–VII.