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

description: Trapezarma angolense (Brito Capello, 1864)
(Figs. 13G, 14G, 16, 18E, 21A–G, 43I)
Sesarma angolensis Brito Capello, 1864: 4, fig. 2; De Man, 1883: 161; Büttikofer, 1890: 487; Johnston, 1906: 861; Longhurst, 1958: 88; Gauld, 1960: 71.
Sesarma (Holometopus) angolensis – De Man, 1900: 59, pl. 2 fig. 11; Tesch, 1917: 130; Dartevelle, 1950: 48; Monod, 1956: 445, fig. 605; Rossignol, 1962: 120.
Sesarma (Holometopus) angolense – Rathbun, 1921: 451, pls. 43, 45 fig. 1; Dartevelle, 1950: 50; Capart, 1951: 191, fig. 76; Rossignol, 1957: 92, 122 [key]; Jordan, 1957: 198; Humes, 1957: 186, 187, 189.
Sesarma (Parasesarma) angolensis – Rathbun, 1900: 280.
Sesarma (Chiromantes) angolense – Manning & Holthuis, 1981: 243.
“ Chiromantes ” angolense – Ng et al., 2008a: 220.
Material examined. ANGOLA – Neotype (here designated): male (39.3 × 32.7 mm) (SMF-ZMG 635 a), Benguella, river mouth of Catumbella near Benguella, coll. M.P. Kammerman; 1 ovigerous female (39.6 × 33.8 mm) (SMF-ZMG 635 b), same data as neotype; 1 male, 2 females (RMNH D 1200), Lobito, coll. P. Kamerman, 1899. CAMEROON – 1 juvenile male (SMF 25982), West Nimbe (Limbe or Victoria), Mile 6, north of Nimbe, between pieces of basalt, coll. C.H. Otto, 7 January 1984; 2 males (35.2 × 28.6 mm, 21.2 × 16.3 mm), 1 female (18.2 × 14.3 mm) (ZRC 2015.0297), Lokoundjié mangrove, coll. P.A. Mvogo-Ndongo, 21 June 2015. LIBERIA – 2 females (RMNH D 1937), coll. J. Demery, 1890–1897.
Diagnosis. Carapace distinctly trapezoidal; frontal margin entire; lateral margins of carapace strongly converging to posterior carapace margin; cheliped merus with inner margin serrated but not expanded; adult male chela stout, outer surface gently convex, in large males, pollex may be expanded, shear-like, more flattened; male thoracic sternites 2–4 narrow in adults, suture between sternites 3 and 4 distinct; male sternopleonal cavity reaching three-quarters length of sternite 4 to just before anterior margin of sternite 2; male thoracic sternite 5 smooth, without depression on anterior part; male pleon elongate, narrow, telson linguiform; G1 relatively stout, chitinous part short.
Colour. The colour was described in detail by Rossignol (1957: 92): carapace blue-green with a yellow margin; ambulatory legs of the same colour as the carapace with a red dot to the joints, end dactylus yellow-orange dactyls; pincers colour of yellow leather with a red spot at the joint of the chela and fingers; eyes with light blue or gray-blue peduncle; cornea brown with a red dot; pleon dirty yellow with a blue median transverse line spanning somite 1; thoracic articles yellow and blue (translated from the French).
Remarks. In naming this species, Brito Capello did not indicate how many specimens he had. All he stated was that the species was from “mares de Angola ” (Brito Capello, 1864: 4). Unfortunately, all of Brito Capello’s material in the Lisbon Museum were lost in a fire in 1978, and the types of this species are no longer extant. While the identity of this species is currently not in doubt, because it is here designated as the type species for Trapezarma, new genus, it is important to ensure a stable taxonomy. As such, we designate a large male specimen in the Senckenberg Museum (SMF-ZMG 635a) as the neotype of Sesarma angolensis Brito Capello, 1864.
There is considerable variation in the form of the male chela. The largest male from Angola (the neotype male) has a more typical chela in which the pollex is relatively slender and the dactylus gently curved (Fig. 16A). In the smaller but clearly adult male from Cameroon, the pollex is strongly expanded, very broad, the outer surface more flattened, and the dactylus is strongly curved (Fig. 16C, D). The specimen figured by Brito Capello (1864: fig. 2c) shows a chela which is more intermediate in form. Other than this, the specimens from Cameroon and Angola are very similar and we have no reason to suspect they are different species. The characteristic male chela (Fig. 16C, D) noted above may be a feature of dominant males.
Biology. The best account of the biology of this species is given in Rathbun (1921: 451–452), who observes that it prefers the more freshwater sections of the river.
Distribution. Sierra Leone to Angola (Monod, 1956; Manning & Holthuis, 1981).
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 936, DOI: 10.26107/RBZ-2020-0097, http://zenodo.org/record/5351295