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

description: Orisarma patshuni (Soh, 1978)
(Figs. 1G, H, 3F, 5H, I, 9H, 12K–O, 33G, 43D, 55)
Pseudosesarma patshuni Soh, 1978: 14, fig. e, f, pl. 1c, f, pl. 3f; Lee, 1995: 3; Kwok & Tang, 2005: 3, fig. 16; Yang et al., 2008: 802.
Sesarma impressum – Wang & Leung, 2001: 31, unnumbered figure. [not Sesarma impressa H. Milne Edwards, 1837]
“ Pseudosesarma ” patshuni – Ng et al., 2008a: 220.
Material examined. Paratypes: 5 males (largest 13.5 × 11.9 mm, smallest 10.8 × 9.6 mm), 2 females (16.9 × 14.7 mm, 16.4 × 14.0 mm) (ZRC 1975.7.1.2–8), Shiu Hau at Lantau Island, Hong Kong, coll. C.L. Soh, 2 June 1975. Others: HONG KONG – 1 male (14.2 × 13.0 mm) (ZRC 1998.345), Hong Kong Island, south coast, Tai Tam immediately downstream of Tai Tam Dam, salt marsh and remnant mangroves, coll. P.K.L. Ng & S.Y. Lee, 6 June 1996; 7 males (largest 23.2 × 20.7 mm), 12 females (largest 20.2 × 17.2 mm) (ZRC 2012.0032), 2 males, 3 females (ZRC 2014.0817), on banks of small freshwater steam next to Tai Tam Dam, under rocks, Tai Tam immediately downstream of salt marsh and remnant mangroves, south coast of Hong Kong Island, coll. P.K.L. Ng et al., 25 December 2011; 2 males (ZRC 2019.1067), on low shrubs on hard mud, back mangroves, ca. 22°29′44.6″N 114°02′49.7″E, Mai Po Nature Reserve, coll. S. Cannicci et al., 24 May 2019.
Diagnosis. Dorsal surface of carapace gently convex, surfaces relatively smooth; frontal lobes separated by distinct concavity; epibranchial tooth distinct, always separated by deep notch; posterolateral margins subparallel; granules on outer surface of palm small but distinct; merus of ambulatory legs relatively slender; chitinous distal part of G1 short but with tip flared. In life, carapace brown; chelae bright purple.
Colour. In life, the carapace and ambulatory legs are dark brown to pale purplish-brown, with the chela violet to purple (Fig. 55), even in females and subadults.
Remarks. Soh (1978) described Pseudosesarma patshuni from one holotype male (14.5 × 13.0 mm, NHM 1976.108) as well as seven males and six females from Lantau Island in Hong Kong. The present material from Hong Kong Island, just east of Lantau Island, agrees very well with the types, except that there are many much larger specimens. The large males agree in almost all aspects with the smaller ones, except that the chelae are stouter and relatively larger. While the smaller males have more delicate chelae, resembling those of many other species of Pseudosesarma (Figs. 1G, 5H), in the large males, the chelae more closely resemble those of other species of Orisarma, being prominently inflated with a distinct longitudinal ridge on the outer surface and a strong transverse ridge on the inner surface (Figs. 1H, 5I).
Soh (1978) noted that it was the only Pseudosesarma species in which the palm of the chela lacked tubercles. This is not strictly correct as the outer surface of the palm of P. patshuni is covered with small granules (Fig. 5H, I), albeit relatively lower and less prominent than those of other Pseudosesarma species. The form of the chela of P. patshuni is close to the condition seen in other Orisarma species, with the possession of median longitudinal ridge on the outer surface and a strong transverse ridge on the inner surface (Figs. 1G, H, 5H, I); and it also shares the same kind of male thoracic sternum and male pleon (Fig. 9H). The characteristically short G1 is also similar in form to those seen in O. intermedium and O. sinense, except that its tip is more distinctly flared (Fig. 12L–O). The above characters are not those now diagnostic for the redefined Pseudosesarma (see later). In the form of the carapace and chelae, P. patshuni actually is intermediate in form between what is observed for one group of species containing O. dehaani, O. neglectum, and O. magnum; and the other with O. intermedium and O. sinense. As such, P. patshuni should be transferred to Orisarma. Compared to other Orisarma species, O. patshuni is also relatively small in adult size, Soh’s (1978) largest specimen was only 14.5 mm in carapace width, and even our largest specimen here only measures 23.2 mm; smaller than the other Orisarma species in which adults average 30 mm in width.
Biology. Soh (1978: 15) noted that the species was found “underneath stones, driftwood and among grasses in the sandy mud zone near the sea” on Lantau Island. On Hong Kong island, it was found under rocks in a wholly freshwater stream adjacent to a salt marsh near a dam, and is probably subjected to some subterranean saline intrusion, although the stream itself is not affected except by the highest tides. They are semiterrestrial in habit.
Distribution. Known from Lantau and Hong Kong islands (Soh, 1978; present data); the species has also been reported from Macau (incorrectly as Sesarmops impressum) by Wang & Leung (2001).
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 920, DOI: 10.26107/RBZ-2020-0097, http://zenodo.org/record/5351295