Parasesarma leptosoma
Creators: name: Li, Jheng-Jhang
name: Rahayu, Dwi Listyo
name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Sesarmidae
Parasesarma
Parasesarma leptosoma

description: Parasesarma leptosoma (Hilgendorf, 1869)
(Figs. 1, 2A–H, 19A, 21A, 24A)
Sesarma leptosoma Hilgendorf 1869: 91, pl. 6, fig. 1.— De Man 1887: 645.—Pfeffer 1889: 31.—Vannini & Ruwa 1994: 271.— Cannicci et al. 1996a: 795.— Cannicci et al. 1996b: 299.— Vannini et al. 1997a: 325, tabs. 1, 3.— Vannini et al. 1997b: 101.— Dahdouh-Guebas et al. 1999: 291.— Cannicci et al. 2002: 77.
Sesarma (Parasesarma) leptosoma, Tesch 1917: 169 (list), 253 (key).— Guinot 1967: 288 (list).
Sesarma (Holometopus) sp., Crosnier 1965: 58, fig. 89.
Parasesarma leptosomum, Hartnoll 1975: 318, tabs. 1–3.
Parasesarma leptosoma, Emmerson et al. 2003: 351.— Fratini et al. 2005: 219.— Emmerson & Ndenze 2007: 13.—Ng et al. 2008: 222 (list).—Rahayu & Ng 2009: 30, 33.— Koller et al. 2010: 359, 365.— Bouchard et al. 2013: 22, Fig. 17.— Emmerson 2016: 263.
Material examined. HOLOTYPE: female (17.5×16.0 mm) (ZMB No. 3 181), East Africa: Tanzania: Zanzibar, no date, v. d. Deckon. Other material: 2 males (17.2×16.0 mm, 16.1× 14.8 mm), 1 female (16.4× 14.7 mm) (ZRC 2017.163), mangrove creek, Mngazana, eastern Cape Province, South Africa, 9–10 March 2017, S. Cannicci. — 1 male (12.0× 13.6 mm) (MNHN B32081), East Africa: Mayotte Island: Malamani mangrove, 2 November 2009, J.M. Bouchard, J. Dumas, V. Dinhut. — 1 male (16.0× 14.8 mm), 1 ovigerous female (14.9× 12.7 mm) (ZRC 2000.1718), East Africa: Kenya: Mida creek, October 1990, M. Vannini.
Diagnosis. Carapace (Figs. 1A, E, G, 2A) trapezoidal; regions well defined, separated by shallow grooves; postfrontal region distinct, separated into 4 lobes by shallow but distinct grooves; front deflexed downwards, margin nearly straight in dorsal view (Figs. 1C, D, 2A); lateral margin straight, distinctly converging towards posterior carapace margin; cornea reaching tip of external orbital tooth (Figs. 1A, E, G, 2A). Ischium of third maxilliped with shallow median sulcus, merus with distinct submedian ridge; exopod slender, tip reaching halflength of outer margin of merus, flagellum long. Male cheliped palm with 2 transverse pectinate crests (14 and 9 corneous teeth, respectively) (Fig. 2B) on upper surface; upper surface of dactylus with 7 asymmetrical dactylar tubercles, proximal 3 tubercles large, tubercles 4–6 smaller, distalmost tubercle indistinct (Figs. 2C, D, 19A). Ambulatory legs (Figs. 1E, G) proportionately stout, P3 and P4 about 1.8 times carapace width; P3 and P4 coxae without dense setae; P3 merus 2.4 times as long as broad; P3 propodus 4.1 times as long as broad; P3 dactylus 0.3 times length of propodus (Figs. 1E, G). G1 straight, relatively slender (Figs. 2E–H, 21A); apical process bent to form an angle of 45°, corneous part short, ending in rounded tip; setae long, simple, originating at base of apical process. G2 longer than quarter length of G1 (Fig. 21A).
Description. Carapace (Figs. 1A, E, G, 2A) trapezoidal, 1.1 times broader than long; regions well defined, separated by shallow grooves; dorsolateral carapace surface lined with strong oblique striae; surface smooth. Postfrontal region distinct, separated into 4 lobes by shallow but distinct grooves; median lobes approximately same width as lateral lobes. Front (Figs. 1C, D, 2A) deflexed downwards, margin nearly straight in dorsal view. 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 straight, distinctly converging posteriorly. Cornea reaching edge of external orbital tooth (Figs. 1A, E, G, 2A). 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 reaching half-length of outer margin of merus, flagellum long.
Chelipeds (Figs. 1E, 2B–D, 19A) relatively large, robust in adult males. Merus with carinate outer margin, without subdistal spine; inner margin with minute tubercles ending in large subdistal protuberance; outer surface with dorsal striation, ventrally tuberculate. Carpus with inner angle not produced. Upper surface of palm with 2 transverse pectinate crests. Distal crest composed of 14 high corneous teeth; second crest well developed, shorter than first crest, with 9 broader corneous teeth; crests followed by several blunt tubercles; rows of small tubercles below second crest. Outer and inner surfaces of palm with numerous granules. Fixed finger rounded, smooth on outer surface; inner surface with median ridge, moderately long. Cutting edge of fixed finger, dactylus with rounded teeth. Dorsal surface of dactylus with 7 asymmetrical tubercles, short, gradually sloping distally. First 3 tubercles large, tubercles 4–6 smaller, tubercle 7 almost indiscernible. Fingers with chitinous tips, proximal gap distinct when fingers closed.
Ambulatory legs (Figs. 1E, G) long, stout, laterally flattened; P3, P4 subequal, longer than others, about 1.8 times carapace width; P3, P4 coxa without dense setae. Merus of P3 2.4 times as long as broad; upper margin of merus with acute subdistal spine. Meri of P2–P5 each with transverse striae on upper surface. Carpi of P2–P5 each with 2 accessory carinae on outer surface. Propodus of P3 4.1 times as long as broad with accessory carina on inferior proximal portion of outer surface, dorsal and ventral margins with short stiff setae. Dactylus 0.3 times length of propodus, tip slightly recurved, terminating in acute calcareous tip, dorsal and ventral margins with short stiff setae.
Thoracic sternites 1–3 completely fused. Male pleon (Figs. 1B, F) 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 more trapezoidal, lateral margins of somites 4, 5 straight, lateral margins of somite 3 strongly convex, somites 1, 2 very narrow longitudinally.
G1 straight, relatively slender (Figs. 2E–H, 21A); apical process slightly bent to form an angle of 45°, produced, corneous part short, ending in rounded tip; setae long, simple, originating at base of apical process. G2 greater than quarter length of G1 (Fig. 21A).
Female (Figs. 1A–C, G, H) with relatively smaller chelipeds, pectinate crest on palms indistinct, dactylar tubercles low. Female pleon broad, telson semicircular. Vulva on anterior edge of sternite 5.
Colour in life. Carapace brown, mottled with darker and lighter blotches, chelipeds reddish brown (Fig. 24A).
Remarks. Parasesarma leptosoma was originally described by Hilgendorf (1869) (as Sesarma) based on a female specimen from Mozambique (ZMB 3181). The holotype examined (Figs. 1A–C) differs slightly from Hilgendorf’s figures (viz. pl. VI, figs. 1, 1c) in general carapace shape but this is certainly due to inaccuracies in the drawing.
Crosnier (1965) listed and figured Sesarma (Holometopus) sp. from Madagascar based on three females, and noted that the merus of P3 is 2.4 as long as broad, with the dactylus one-third the length of the propodus. The measurements (Table 1), the figure of the carapace, and the proportions of the merus and dactylus of the P3 match P. leptosoma. In ZMB there is a male specimen (17.2× 16.2 mm, ZMB 3181) labelled as “ Sesarma leptosoma ”, collected from Madagascar. This specimen closely resembles typical P. leptosoma in the carapace shape and proportions of the ambulatory legs, but the chela does not have any pectinate ridges and the dorsal margin of the dactylar finger is unarmed, and so cannot be a species of Parasesarma. It is here reidentified as Armases elegans (Herklots, 1851), a species known thus far only from the eastern Atlantic, although its superficial similarity in the body form to P. leptosoma is remarkable.
The most obvious character that easily distinguishes P. leptosoma from the other members in the speciescomplex is the shape of the carapace and proportions of the ambulatory legs. The lateral-margin of the carapace is distinctly convergent posteriorly and the frontal margin is almost straight, which contribute to the distinctly trapezoidal shape of carapace (Figs. 1A, E, G, 2A). Furthermore, the ambulatory legs of P. leptosoma (Figs. 1E, G) are proportionately the broadest among members of this complex.
Questionable records. Old records of P. leptosoma sensu lato pose problems as they often do not provide good figures and/or enough characters to enable a verification of their specific identities. De Man (1895) listed eight species of Parasesarma (including P. leptosoma) from the Java Sea and nearby locations, Malaka (= Peninsular Malaysia), Borneo and Celebes (= Sulawesi), but all were only briefly described in the key. De Man (1895: 182) wrote about his P. leptosoma: “Dactylopoditen der Lauffüsse ausserordentlich kurz, ein Drittel der Propodusten messend” (= the ambulatory dactylus is short, being only about a third of the length of the propodus). Such features suggest that De Man’s species is probably a member of the P. leptosoma species-complex.
Distribution. South and East Africa: Somalia, Kenya, Mozambique, Tanzania (Hilgendorf 1869; Hartnoll 1975; De Man 1887; Pfeffer 1889; Vannini & Ruwa 1994; Cannicci et al. 1996a, b, 2002; Emmerson et al. 2003; Fratini et al. 2005; Emmerson 2016), Mayotte (Bouchard et al. 2013) and Madagascar (Crosnier 1965; Guinot 1967).
Ecology. Parasesarma leptosoma is known to be one of the exclusively arboreal crabs (Vannini et al. 1997b) and was referred as possessing the highest tree-climbing degree, i.e. a “TC (tree-canopy) species” as defined by Fratini et al. (2005). Ng et al. (2015) noted that these crabs could be regarded as obligate tree-dwelling or arboreal taxa. The behavior of P. leptosoma s. str. is well-documented. The species is found above the supratidal zone and lives exclusively on two mangrove trees, Rhizophora mucronata Lam. and Bruguiera gymnorrhiza (L.) Lam. (Emmerson et al. 2003; Emmerson & Ndenze 2007), but few were found in the Ceriops zone of creek mangrove (Hartnoll, 1975). The species was recorded climbing the entire tree to feed on fresh leaves (Vannini & Ruwa 1994; Cannicci et al. 1996a, b; Dahdouh-Guebas et al. 1999; Fratini et al. 2005; Emmerson 2016), with some vertical migrations (Vannini et al. 1995), and has been observed to possess homing behavior (Cannicci et al. 1997). Apart from the breeding period, the species rarely ventured onto the mudflat nor into the water. It always kept itself above the water level on the tree trunk or aerial root (Vannini et al. 1997a). It has been observed to perform wellsynchronized mass migrations to and from the tree canopy twice a day (Cannicci et al. 1996; Vannini et al. 1997a).
description: Published as part of Li, Jheng-Jhang, Rahayu, Dwi Listyo & Ng, Peter K. L., 2018, Identity of the tree-spider crab, Parasesarma leptosoma (Hilgendorf, 1869) (Decapoda: Brachyura: Sesarmidae), with descriptions of seven new species from the Western Pacific, pp. 451-490 in Zootaxa 4482 (3) on pages 452-456, DOI: 10.11646/zootaxa.4482.3.2, http://zenodo.org/record/1440707