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

description: Bresedium laevimanum (Zehntner, 1894)
(Figs. 24E–H, 26C, D, 29D–F, 31F–H, 42)
Sesarma Edwardsi var. laevimana Zehntner, 1894: 181, 182.
Sesarma edwardsi var. laevimana – Lanchester, 1900: 757.
Sesarma (Sesarma) edwardsi laevimana – Tesch, 1917: 148.
Sesarma sediliensis Tweedie, 1940: 100, fig. 8, pl. 24-2; Tweedie, 1950: 342.
Sesarma (Sesarma) edwarsi laevimanum – Tan & Ng, 1994: 82; Serène, 1968: 105.
Pseudosesarma laevimanum – Ng et al., 2008a: 222.
Pseudosesarma laevimana –? Naiyanetr, 1998: 102;? Naiyanetr, 2007: 116.
Bresedium sediliensis – Ng & Tan, 1994: 82.
Bresedium sedilensis [sic] – Ng et al., 2008a: 220.
Material examined. Lectotype (here designated): male (20.0 × 17.6 mm) (MNHG), coll. “ Indes Neerlandische ”, Bedot & Pichet, 1800s. Paralectotypes: 2 males (16.7 × 15.3 mm, 10.5 × 9.3 mm), 2 females (10.4 × 9.3 mm, 6.8 × 5.8 mm) (MNHG), Sarawak, coll. Bedot & Pichet, 1800s. Others: PENINSULAR MALAYSIA – 1 male (26.3 × 23.7 mm) (NHM) (lectotype of Sesarma sediliensis Tweedie, 1940, here designated), Sedili River, Johor, coll. M.W.F. Tweedie, March 1938; 1 female (22.8 × 19.7 mm) (NHM) (paralectotype of Sesarma sediliensis Tweedie, 1940), Sedili River, Johor, coll. M.W.F. Tweedie, March 1938; 37 males (largest 21.2 × 18.2 mm), 22 females (largest 20.3 × 17.8 mm) (ZRC 1965.7.29.121–133), Sedili River, Johor, coll. M.W.F. Tweedie, March 1938. SARAWAK – 19 males (largest 20.1 × 17.9 mm), 17 females (largest 19.2 × 16.7 mm, 2 ovigerous) (ZRC 1972.3.7.25–35), water ditch, Kuching, coll. M.W.F. Tweedie, January 1949.
Diagnosis. Carapace transversely rectangular; epibranchial tooth distinct, separated by deep notch; posterolateral margins subparallel; outer surface of chela relatively smooth, punctate, or with scattered low granules, ventral margin of palm sinuous, smooth; suture between male thoracic sternites 3 and 4 visible; ambulatory merus short, broad; male pleon somewhat elongate, subrectangular, telson distinctly sunken into distal margin of somite 6; G1 very slender, straight, chitinous distal part long, with tip prominently flared.
Colour. “In life the chelipeds are bright red and the carapace dark brown, more or less variegated with greenish.” (Tweedie, 1940: 102).
Remarks. The identity of this species has been uncertain since its original description as no figures were provided. Zehntner (1894) regarded it as a variety of Sesarma edwardsii, and most subsequent workers have followed this association. Comparison of the types of Sesarma edwardsi var. laevimana from the Muséum national d’Histoire naturelle, Geneva, with type material of Sesarma sediliensis, leave no doubt that Zehntner’s (1894) variety is identical with Bresedium sediliensis (Tweedie, 1940). The broadly rectangular carapace (Figs. 24E–H), subrectangular male pleon with the telson sunken into somite 6 (Figs. 31F–H, 42A) and the characteristic G1 with the tip expanded (Fig. 42B–E) are typical for members of this genus. Sesarma sediliensis Tweedie, 1940, was transferred to Bresedium by Serène & Soh (1970).
Tweedie (1940: 100–103, fig. 8, pl. 24-2) described Sesarma sediliensis from one male and one female which he labelled as cotypes and “a series of sub-adult specimens from the type locality”. The way this sentence is phrased means he only regarded the male and female specimens mentioned (both of which are now in NHM) as syntypes, and the rest are not types. The male (26.3 × 23.7 mm) is here designated as the lectotype of the species to stabilise the taxonomy. In the ZRC are two lots, ZRC 1965.7.29.121–133 (from Johor) and ZRC 1972.3.7.25–35 (from Sarawak), both of which are listed as paratypes. They are therefore not types, even though the Johor material was collected at the same time by Tweedie as the syntypes. The Johor lot (ZRC 1965.7.29.121–133), however, are not sub-adults, with most of the specimens large and fully adult, even though none of the females are ovigerous.
Biology. According to Tweedie (1940: 103), “These crabs were found among the stems of nipah palms (Nipah fruticans) growing in mud on the banks of the river Sedili. The water in the part of the river where the palms grow is slightly brackish with incursions of fresh water when the river floods. Its salinity never approaches that of the open sea.”
Distribution. Known from Southern Peninsular Malaysia and Sarawak, and perhaps Thailand (Tweedie, 1940, 1950; Naiyanetr, 1998, 2007).
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 pages 966-967, DOI: 10.26107/RBZ-2020-0097, http://zenodo.org/record/5351295