Orisarma Schubart & Ng 2020, new genus
Creators: name: Schubart, Christoph D.
name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Sesarmidae
Orisarma

description: Orisarma, new genus
Type species. Sesarma dehaani H. Milne Edwards, 1853, by present designation. Gender neuter.
Diagnosis. Carapace squarish to transversely subrectangular; frontal margin distinctly bilobed, gently deflexed, as wide as or slightly wider than posterior carapace margin; lateral margins of carapace entire, gently lobulated or with one epibranchial tooth, posterolateral part gently convex to subparallel; regions of carapace distinct to prominently demarcated; postfrontal and epigastric crests separated by relatively deep or distinct grooves, margin usually relatively rounded, regions clearly separated; basal articles of antenna and antennules clearly separated by septum formed by extension of front; dorsal margin of palm without any longitudinal pectinated ridge; in adult males, inner surface with prominent submedian transverse swelling, highest point with transverse ridge of granules, outer surface of palm and pollex convex, outer surface of palm usually with short longitudinal median smooth ridge (sometimes very low, obscured by granules); dorsal margin of chelipedal dactylus smooth, if small granules present, scattered, never in distinct row or of regular shape; inner distal margin of merus of cheliped not lamelliform; inner surfaces of first to third ambulatory coxae with only scattered short setae among them, not arranged into dense tufts; male thoracic sternites 2–4 relatively narrow in adults, suture between sternites 3 and 4 shallow, sometimes appearing medially interrupted; male sternopleonal cavity reaching two-thirds length of sternite 4 to just before anterior margin of sternite 2; male thoracic sternite 5 smooth, without depression on anterior part; G1 relatively slender, long or short, stout, chitinous part relatively short. Vulva on anterior part of sternite 6, anterior edge presses against sternite 5; anterior sternal vulvar cover very low, posterior sternal vulvar cover low, rim-like; opening projecting, directed anteriorly to obliquely anteriorly.
Etymology. The name is derived from the arbritary combination of the term for East Asia, “Oriental”, and the genus name Sesarma. The gender is neuter.
Included species. Sesarma dehaani H. Milne Edwards, 1853 (= Sesarma hanseni Rathbun, 1897); Sesarma neglecta De Man, 1887; Chiromantes magnus Komai & Ng, 2013; Grapsus (Pachysoma) intermedius De Haan, 1835; Sesarma sinensis H. Milne Edwards, 1853; Pseudosesarma patshuni Soh, 1978.
Remarks. The major differences between Orisarma and Chiromantes s. str. have been discussed under the latter genus. In addition to Chiromantes dehaani (H. Milne Edwards, 1853) and C. neglectus (De Man, 1887), two species of Sesarmops and one species of Pseudosesarma also need to be placed in Orisarma. As Serène & Soh (1970) had suspected (see Introduction), Sesarmops intermedius (De Haan, 1835) and S. sinensis (H. Milne Edwards, 1853) are more closely related to each other and to species of Orisarma. Surprisingly, we also find that all the morphological characters of the small species, Pseudosesarma patshuni Soh, 1978, also agree with Sesarmops intermedius and S. sinensis, including the form of the thoracic sternum, male chela with a low median longitudinal ridge, relatively wide male pleons, proportionately long ambulatory legs, structure of their G1s (Figs. 1G, H, 3F, 5H, I, 9H, 12K–O) and even in the structure of the vulvae (Fig. 43D). The closest genus to Orisarma may be Manarma, new genus, which consists of two species, M. moeschii (De Man, 1892) and M. johorensis (Tweedie, 1940). These two species, as already highlighted by Serène & Soh (1970), are characterised by their shiny carapaces, narrow thoracic sterna, narrow male pleons, and form of their G1s (cf. Figs. 24C, D, 26A, B, 29B, C, 33A, B, D, E, 58).
The remaining species of Sesarmops Serène & Soh, 1970 (type species Sesarma impressa H. Milne Edwards, 1837), have more trapezoidal carapaces and a relatively stout G1 with a very long chitinous distal process. One species still in Sesarmops, S. weberi (De Man, 1902), does not belong to this genus on account of its short G1 and a male chelipedal dactylar finger that has a row of stridulatory granules on the dorsal margin (see Ng et al., 2008a: 224; Naruse & Ng, 2020). Ng et al. (2008a) suggested the species was close to Labuanium trapezoideum (H. Milne Edwards, 1837) but Naruse & Ng (2020) showed otherwise. The systematic position of this species should be dealt with when Sesarmops is completely revised.
description: Published as part of Schubart, Christoph D. & Ng, Peter K. L., 2020, Revision of the intertidal and semiterrestrial crab genera Chiromantes Gistel, 1848, and Pseudosesarma Serène & Soh, 1970 (Crustacea: Brachyura: Sesarmidae), using morphology and molecular phylogenetics, with the establishment of nine new genera and two new species, pp. 891-994 in Raffles Bulletin of Zoology 68 on page 904, DOI: 10.26107/RBZ-2020-0097, http://zenodo.org/record/5351295