Parasesarma paucitorum Rahayu & Ng, 2009, n. sp.
Creators: name: Rahayu, Dwi Listyo
name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2009
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Sesarmidae
Parasesarma
Parasesarma paucitorum

description: Parasesarma paucitorum n. sp.
(Figs. 1–4)
Material examined. HOLOTYPE: male (19.7 x 17.8 mm) (MZB), Manado, northern Sulawesi, Indonesia, coll. P. K. L. Ng. 17 July 2003. PARATYPES: 1 male (15.5 x 13.6 mm), 1 ovigerous female (19.2 x 17.6 mm) (ZRC 2008.0869), same data as holotype.
Comparative material. Parasesarma leptosoma (Hilgendorf, 1869): 1 male (16.0 x 14.8 mm), 1 ovigerous female (14.9 x 12.7 mm) (ZRC 2000.1787), Mida Creek, Kenya, coll. M. Vannini, October 1990. – 2 males (10.1 x 9.8 mm, 9.8 x 9.2 mm) (ZRC 1965.8.2.1-2), Kuantan, Pahang, Peninsular Malaysia, coll. September 1935. – 1 female (12.5 x 10.7 mm) (ZRC 2000.1881), Ajkwa River, Papua, Indonesia, coll. G. Setyadi, 3 August 1999. – 1 male (12.6 x 10.9 mm) (ZRC 2000.1882), Minajerwi, Papua, Indonesia, coll. G. Setyadi, 12 August 1999. – 1 male (14.2 x 12.0 mm) (ZRC 2000.1883), Kamora, Papua, Indonesia, coll. D. L. Rahayu, 4 April 2000. – 1 male (14.5 x 12.3 mm) (ZRC 2008.0501), Pago Bay, Guam, coll. H.-C. Liu, August 2001.
Etymology. From the Latin “ pauci ” for a small number, and “ torum ” for protuberances, alluding to the relatively low number of tubercles on the dorsal surface of the cheliped dactylus.
Diagnosis. Carapace 1.1 times broader than long; regions of carapace well defined; postfrontal region separated into 4 lobes by narrow, deep grooves; frontal margin bilobed from dorsal view, each lobe broadly convex; external orbital tooth directed obliquely outwards; eyes not extending beyond edge of external orbital tooth; upper surface of cheliped palm with 2 transverse pectinated crests (16 and 9 corneous teeth, respectively); outer surface of palm striated proximally, distally granular, inner surface with numerous tubercles; dorsal surface of dactylus with 9 asymmetrical tubercles (first 3 largest), short, steep proximally, gradually sloping distally; each dactylar tubercle with proximal part lined with longitudinal lines, distal part with transverse lines, summit with distinct ridge; ambulatory legs slender; merus of third leg 2.7 times as long as wide; upper margin of merus with acute subdistal spine; propodus of third leg 4 times as long as wide; dactylus 0.8 times length of propodus; male telson semicircular, evenly rounded, as long as somite 6; G1 straight; apical process slightly bent at an angle of 60º, corneous part short, ending in truncate tip.
Description. Carapace 1.1 times broader than long; all regions of carapace clearly defined, separated by well marked grooves; lateral carapace surface lined with strong oblique striae; carapace surface, lateral margins with numerous tufts of short setae. Postfrontal region distinct, separated into 4 lobes by narrow, deep grooves; median lobes approximately same width as lateral lobes. Front deflexed downwards, margin bilobed from dorsal view, each lobe broadly convex, separated by very broad median concavity. Supraorbital margin gently convex, entire. External orbital tooth triangular, directed obliquely outwards, representing point of greatest width; contiguous with entire lateral carapace margin; antero- and posterolateral margins not demarcated, without trace of tooth or indentation, lateral margin gently sinuous, subparallel along most of length before curving to join almost straight posterior carapace margin. Eyes not extending beyond edge of external orbital tooth. Antennal and antennular basal segments adjacent, not separated by septum; basal antennular segment swollen. Antennal flagellum relatively long, entering orbit. Ischium of third maxilliped with shallow median sulcus, merus with distinct submedian ridge; exopod slender, tip overreaching half length of outer margin of merus, flagellum long; inner margin of merus, ischium with long setae, proximal outer margin of ischium, base of exopod with long, densely packed setae.
Chelipeds relatively large, robust in adult males. Merus with carinated outer margin, without subdistal spine; inner margin with minute tubercles ending in large subdistal protuberance; outer surface with dorsal striation, ventrally tuberculated, inner surface with 2 longitudinal rows of setae. Carpus with inner angle not produced, outer margin, across dorsal surface tuberculate. Upper surface of palm with 2 transverse pectinated crests. First crest composed of 16 high corneous teeth; second crest well developed, shorter than first crest, with 9 broader, more widely spaced corneous teeth; crests followed by several blunt tubercles; rows of small tubercles below second crest. Outer surface of palm striated proximally, distally granular, glabrous; inner surface of palm with numerous tubercles. Fixed finger rounded, smooth on outer surface; inner surface with median ridge, moderately long. Cutting edge of fixed finger, dactylus with small, large rounded teeth. Dorsal surface of dactylus with 9 asymmetrical tubercles, short, steep proximally, gradually sloping distally. Proximal part of tubercles with longitudinal fine lines, distal part with transverse lines, distinct ridge on summit; first 3 tubercles small, low, tubercles 4–7 large, tubercles 8, 9 almost indiscernible; several low tubercles on proximal third between dactylar tubercles, outer edge of dactylus. Fingers with chitinous tips, proximal gape distinct when fingers closed.
Ambulatory legs long, slender, laterally flattened; second, third pairs subequal, longer than others, about 1.7 times carapace width. Merus of third leg 2.7 times as long as wide; upper margin of merus with an acute subdistal spine. Meri of legs 1–4 each with transverse striae on upper surface. Carpi of legs 1–4 each with 2 accessory carinae on outer surface. Propodus of third leg 4 times as long as wide with accessory carina on inferior proximal portion of outer surface, dorsal and ventral margins with short stiff setae. Dactylus 0.8 times length of propodus, tip slightly recurved, terminating in acute calcareous tip, dorsal and ventral margins with short stiff setae.
Surfaces of thoracic sternites 1–3 setose. Sternites 1–3 completely fused. Sternites 3, 4 separated by low ridge lined with short, densely packed setae. Male abdominal cavity reaching just below low ridge separating sternites 3, 4. Male abdomen relatively broad, all somites free. Telson semicircular, evenly rounded, as long as preceding somite; somite 6 almost twice as long as wide, lateral margins slightly convex. Somites 3–5 progressively more trapezoidal, lateral margins of somites 4, 5 straight, lateral margins of somite 3 strongly convex, somites 1, 2 very narrow longitudinally. G1 relatively stout, straight; apical process slightly bent to form an angle of 60º, produced, corneous part short, ending in truncate tip; setae long, simple, originating at base of apical process, on palp. G2 very short, less than quarter length of G1.
Female with relatively small chelipeds, pectinated crest on palms not distinct, dactylar tubercles low.
Colour. In life, the dorsal surfaces of the carapace and pereopods of the holotype male are dark grey to almost black in parts with light grey patches giving the animal a somewhat mottled appearance (Fig. 1 A). In the smaller paratype male, the colour overall is generally lighter with more yellow (Fig. 1 B). There are dark patches forming a broken band across the deflexed frontal margin (Fig. 2 A). The ventral surfaces are white (Fig. 1 C). The chelipeds are orange in the smaller paratype male and female (Fig. 2 A) but become more yellowish in the large male (Fig. 2 B), with the dorsal part of the dactylus purple (Fig. 1 A) rather than orange (Fig. 1 B).
Remarks. The proportionately more slender ambulatory legs and relatively small number of dactylar tubercles on the cheliped places this species closest to Parasesarma leptosoma (Hilgendorf, 1869). In the latter species, however, the ambulatory dactylus is short, being only about a third of the length of the propodus, while in P. paucitorum n. sp. the dactylus is only slightly shorter than the propodus (Figs. 1 A, B, 3A). The shape of the male dactylar tubercles is also quite different. Parasesarma paucitorum n. sp. has asymmetrical tubercles, the proximal part being lower than the distal (Fig. 3 E) while P. leptosoma has symmetrical ones.
The carapace of P. leptosoma is proportionately longer than that of the new species, with the carapace appearing squarish while in P. paucitorum n. sp. the carapace is distinctly wider than long and appears transversely rectangular (Fig. 3 A). In addition, the G1 of P. paucitorum n. sp. is relatively stout, with a short and relatively broad tip (Fig. 4 A–D), while that of P. leptosoma is slender, with a long corneous tip. Ecologically, the two species have very different niches. Parasesarma leptosoma is a tree-dwelling species (Cannici et al. 1996; Fratini et al. 2005) while P. paucitorum n. sp. lives on the ground (see later).
Parasesarma leptosoma has long been characterized by its very short ambulatory dactylus, which is only one-third the length of the propodus. The ZRC lots identified as P. leptosoma show this character and superficially resemble each other. It was noted, however, that the specimens from Kenya, Peninsular Malaysia, Papua (Indonesia) and Guam all differ from each other in the form of the carapace, structure of the dactylar tubercles and G1 form, suggesting that what is presently known as P. leptosoma is actually a complex of several species. Clearly, a revision of P. leptosoma is necessary. One subjective junior synonym of the species, Sesarma (Holometopus) limbense Rathbun, 1914 (see Ng et al. 2008), described from the Philippines, will also need to be examined. This exercise, however, is outside the scope of the present investigation. With regards to P. paucitorum n. sp., however, all the discussed differences still apply.
The only female specimen of P. paucitorum n. sp. is differs slightly from the two smaller males in being generally darker in coloration, the ambulatory meri and propodi are relatively longer, with the postfrontal crests somewhat stronger and the frontal margin less convex. These differences can be explained by its large size.
Parasesarma paucitorum n. sp. was collected from muddy substrates in a coastal mangrove forest with mostly freshwater influence. The crabs were found in burrows dug under rocks and were active only at night. Sesarmids collected with it include Bresedium philippinense (Rathbun, 1914), Labuanium trapezoideum (H. Milne Edwards, 1837), Sesarmops mindanaoensis (Rathbun, 1914) and Sesarmops impressus (H. Milne Edwards, 1837).
Distribution. So far only known from northern Sulawesi, Indonesia.
description: Published as part of Rahayu, Dwi Listyo & Ng, Peter K. L., 2009, Two new species of Parasesarma De Man, 1895, from Southeast Asia (Crustacea: Decapoda: Brachyura: Sesarmidae), pp. 29-40 in Zootaxa 1980 on pages 30-35, DOI: 10.5281/zenodo.185266