Manarma, Schubart & Ng, 2020

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, Raffles Bulletin of Zoology 68, pp. 891-994 : 962

Manarma , new genus

Type species. Sesarma moeschii De Man, 1892 , by present designation. Gender neuter.

Diagnosis. Carapace transversely rectangular; frontal margin bilobed, gently deflexed, as wide as or slightly wider than posterior carapace margin; lateral margins of carapace with epibranchial tooth, posterolateral part subparallel; regions of carapace prominently demarcated; postfrontal and epigastric crests separated by relatively deep or distinct grooves, margin 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 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 with short longitudinal median smooth ridge; dorsal margin of chelipedal dactylus almost 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 three-quarters length of sternite 4 to just before anterior margin of sternite 2; pleonal locking mechanism formed by low angular projection on posterior edge of sternite 4 of sternopleonal cavity, no trace of tubercle on sternite 5; male thoracic sternite 5 smooth, without depression on anterior part; G1 relatively slender, long, chitinous part relatively long. Vulva on anterior part of sternite 6, anterior edge presses against sternite 5; anterior sternal vulvar cover low, rim-like, posterior sternal vulvar cover slightly raised; opening low, tip flattened, uneven, not projecting.

Etymology. The name is derived by combining the name of the carcinologist Johannes Govertus de Man (1850–1930) with the genus name Sesarma . This honours the substantial contributions he has made to our knowledge of sesarmid diversity in the Indo-West Pacific. The gender is neuter.

Included species. Sesarma moeschii De Man, 1892 ; Sesarma johorensis Tweedie, 1940 .

Remarks. Pseudosesarma moeschii ( De Man, 1892) and P. johorense ( Tweedie, 1940) differ markedly from other species of Pseudosesarma in having a carapace that is distinctly transversely rectangular, the regions on the dorsal surface are prominent and glossy, the outer surface of the adult male chela has a distinct longitudinal ridge with the inner surface possessing a strong transverse submedian granulated ridge, the male pleon is relatively narrow and the G1 is elongated and slender. In addition, adult male specimens of most Pseudosesarma species have a slight depression on the anterior part of thoracic sternite 5 in which the tip of the G1 rests when the pleon is closed (see Remarks for Pseudosesarma ). This depression is absent in P. moeschii and P. johorense . It is also not discernible in members of the other genera studied here. The characters discussed are significant enough to warrant the removal of P. moeschii and P. johorense to their own new genus, Manarma . This decision is also well supported by the genetic data which shows these two species to be in their own deep clade basal to Pseudosesarma , Bresedium , and Sesarmops ( Fig. 59 ). While Manarma superficially resembles Orisarma , new genus, in many of the above characters, it is nevertheless easy to distinguish them. The male pleon of species of Manarma is proportionately more slender and elongate ( Fig. 33A, B ) (versus proportionately broader in Orisarma species , e.g., Fig. 9C–H ) and the ambulatory dactylus is relatively shorter ( Fig. 33H ) (versus distinctly longer in Orisarma species , e.g., Fig. 33F, G ).

Figures

Fig. 59. Phylogenetic relationships among selected taxa of Sesarmidae (91 OTUs), including all representatives of Chiromantes and Pseudosesarma previous to current revision of these genera. In addition, several species of Bresedium and Sesarmops are considered, as the revision also involves some of their former members. Topology and confidence values were determined by means of a phylogenetic reconstruction based on 1,096 basepairs of mtDNA (16S-tRNALeu-ND1), conducted with MrBayes, GTR+I+G as substitution model, and Parasesarma plicatum as outgroup (midpoint rooting). Posterior probabilities were determined after 4 million generations with a burn-in of 25%. All species so far classified within Chiromantes (without obvious anterolateral teeth) are shaded in blue, whereas those species that used to be classified in Pseudosesarma (carrying at least one pair of anterolateral teeth) are shaded in yellow.

Fig. 33. A–E, male anterior thoracic sternum and pleon; F–H, left ambulatory leg. A, D, H, Manarma moeschii, male (18.2 × 16.3 mm) (ZRC 2000.1926), Thailand; B, E, M. johorense, male (14.6 × 12.6 mm) (ZRC 1971.9.24.14), Seletar River, Singapore; C, F, Orisarma intermedium, male (34.7 × 31.6 mm) (ZRC 2001.0034), Pingtung, Taiwan; G, O. patshuni (, male (14.2 × 13.0 mm) (ZRC 1998.345), Hong Kong.

Fig. 9. Male anterior thoracic sternum and pleon. A, Chiromantes haematocheir, lectotype male (33.7 × 29.7 mm) (RMNH-D160), Japan; B, C. ryukyuanus, holotype male (33.1 × 29.6 mm) (RUMF-ZC-539), Okinawa Island, Japan; C, Orisarma dehaani, lectotype male (39.5 × 35.7 mm) (RMNH-D157), Japan; D, O. neglectum, neotype male (35.6 × 31.8 mm) (ZRC 1998.310), Shanghai, China; E, O. intermedium, lectotype male (23.0 × 19.9 mm) (RMNH-D165), Japan; F, O. sinense, lectotype male (19.0 × 16.6 mm) (MNHN-BP3635a), China; G, O. sinense, male (29.6 × 25.4 mm) (ZRC 1998.1204), Shanghai, China; H, O. patshuni, male (14.2 × 13.0 mm) (ZRC 1998.345), Hong Kong.