Parasesarma rahayuae Shahdadi & Schubart & Mendoza 2023, n. sp.
Creators: name: Shahdadi, Adnan
name: Schubart, Christoph D.
name: Mendoza, Jose Christopher E.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Sesarmidae
Parasesarma
Parasesarma rahayuae

description: Parasesarma rahayuae n. sp.
(Figs. 2‒4, 5A, D, 6A, D, G)
Material examined. Holotype: MZB 5709 (ex. ZRC 2019.1055), male (11.47×10.11), Indonesia, Sulawesi, Manado, Bitung, Pulau Lembeh, Mawali Bay, mangrove near NAD Resort, coll. H.H. Tan, 01.12.2018; Paratypes: ZRC 2019.1055, 3 males (11.32 × 9.6; 10.87 × 9.4; 10.86 × 9.42), 6 females ((ovig. 11.90 × 9.77; ovig. 11.47 × 9.35; ovig. 10.93 × 9.12; ovig. 9.88 ×8.71; 9.1 ×7.7; 7.67 × 6.54), same data as the holotype.
Comparative material. Parasesarma anambas Yeo, Rahayu & Ng, 2004: ZRC 2003.0726, paratypes, 1 male, 1 female, Indonesia, Anambas Islands, eastern Pulau Siantan, Teluk Baruk, Sungei Temburun, Air Terjun waterfall, stn. EA-JL05.
Parasesarma gemmatum Li, Shih & Ng, 2019, ZRC 2019.1076, paratypes, 1 male, 1 ovig. female, Taiwan, Pingtung, Kenting, Tanzih fishport; ZRC 2023.0256, 1 male, Philippines, Cebu Island.
Diagnosis. Relatively long ambulatory legs. Carapace subquadrate, slightly broader than long, dorsal surface entirely covered with small granules, front moderately deflexed, sinuous in dorsal view, median postfrontal lobes slightly broader than lateral ones. Eyestalk longer than wide, cornea wider than eyestalk. Chelipeds without subdistal spine on dorsal border of merus; male chela with two transverse pectinated crests on the upper surface of palm, dactylus with 17‒19 transverse, broadly ovate tubercles. Male pleon triangular, somite 2 medially as long as lateral edges. G1 stout, straight, apical corneous process relatively long, bent at an angle of ~80° to vertical axis, aperture subterminal.
Description. Maximum cw of material examined = 11.90 mm. Carapace (Figs. 2A, 3A, 4A) subquadrate, slightly broader than long, greatest width between exorbital angles (holotype cw/cl = 1.1); dorsal surface with small granules scattered all over (Fig. 2C); front in holotype ~0.53× carapace width, moderately deflexed, sinuous in dorsal view; postfrontal lobes (Fig. 2D) low but distinct, median lobes slightly broader than lateral lobes, separated by shallow furrow; dorsal regions moderately well indicated, gastric region demarcated, cardiac region separated from intestinal region; lateral branchial ridges prominent; anterolateral margin with sharp exorbital angle directed obliquely; lateral margins straight with no indication of epibranchial tooth, edged with row of short setae. Eyestalk longer than wide, cornea wider than eyestalk.
Chelipeds homochelous (Fig. 2A, B, 3A); chelae (Fig. 2B) large (palm length ~0.75× carapace width in holotype), robust (length ~1.6× palm width in holotype). Merus with granulate dorsal border, but no subdistal spine; ventral border granulate; anterior border granulate, with large subdistal spine; inner face smooth with a longitudinal rows of setae (Fig. 3B). Upper surface of palm with two transverse pectinated crests and a third crest consisting of granules (Fig. 2D, E, 3D), distal (primary) crest composed of 10 or 11 tall teeth (varying on opposite claws of holotype), secondary crest well-developed, with 7 teeth; both crests ending on inner side in short swollen, tubercular ridge (Fig. 3D) and several small granules at outer side; upper margin of palm with scattered setae; outer surface of palm with few scattered setae, granular except for smooth, punctate fixed finger (Fig. 2F); inner surface of palm generally smooth, except for some granules forming a low vertical ridge; ventral border of chela sinuous; length of cutting margin of fixed finger of holotype ~0.4× length of entire propodus. Dactylus (Fig. 2E‒H) slightly curved downward and inward, ~0.6× propodus length in holotype; dorsal surface bearing 17–19 transversely broadly ovate tubercles (Figs. 2E‒H, 3C), distinct to tip, proximal tubercles with transverse keel and longitudinal wrinkles, proximal tubercles positioned at inner part of upper dactylar face, row of ~6 rounded tubercles on proximal onethird of inner edge of dorsal surface; fingers with chitinous tips, cutting edge of both fingers with a series of variably sized teeth (Fig. 2F).
Ambulatory legs (Figs. 2A, B, I, 3A, 4A) relatively long; P4 longest, length (ischium–dactylus) ~1.8× carapace width, merus with anterior margin crenulated, ~2.3× as long as wide, propodus ~3.3× as long as wide, dactylus length ~0.9× length of propodus (all measures from holotype).
Male pleon (Fig. 2B, J) triangular; telson slightly longer than basal width, slightly longer than somite 6; somite 6 longer than others; somite 5 and 4 trapezoidal, somite 3 widest, laterally convex, somite 2 medially as long as lateral edges.
G1 (Figs. 3E‒H, 6A) stout, straight, stem triangular with blunt angles in cross-section; apical corneous process relatively long, bent at an angle of ~80° to vertical axis, arched in cross-section, distinctly wider than the rest of the apical corneous process when seen from the dorsal (sternal) view, aperture subterminal.
Females (Fig. 4) with smaller chelipeds than in males; pectinated crest absent on palm, replaced by rows of granules; dactylus with 5 or 6 small, round tubercles on proximal half (Fig. 4D). Pleon (Fig. 4B) broad, evenly ovate, broadest at somites 4 and 5, fringed with long setae, touching coxae of ambulatory legs. Vulva (Fig. 4C) in depression on anterior edge of sternite 6, operculum touching line of sternite 5, oval operculum in anterior part with a sternal cap (cover) posterior to operculum.
Etymology. The new species is warmly dedicated to and named after Professor Dwi Listyo Rahayu (National Research and Innovation Agency, formerly the Indonesian Institute of Sciences), for her work on the genera Parasesarma and Perisesarma, making significant contributions to our taxonomic understanding of these genera.
Remarks. Corresponding to the molecular phylogenetic relationships, Parasesarma rahayuae n. sp., is also morphologically similar to P. gemmatum and P. anambas. These three species are small crabs (all known individuals less than 15 mm in carapace width) with a subquadrate carapace (Fig. 5A‒C) and a large number (more than 15) of transversely oval tubercles on the dactylus of the male chela (Fig. 5E‒F; Yeo et al. 2004: fig. 2; Li et al. 2019: figs. 9, 10). The new species, however, differs from these two species in a number of morphological characteristics.
Parasesarma gemmatum lacks the pectinated crests on the dorsal surface of the male palm (Fig. 5F), while P. rahayuae n. sp. has two pectinated crests on the dorsal face of the palm (Fig. 5D), like most other Parasesarma. The G1 of P. gemmatum has a proportionally shorter and wider apical corneous process in a more upright position (approximately 45 degrees from the vertical axis; Fig. 5C) in comparison to the longer, narrower, and more bent process in P. rahayuae n. sp. (almost 90° from the vertical axis; Fig. 5A). Compared to P. anambas, P. rahayuae n. sp. has relatively broader tubercles on the dorsal face of the male cheliped dactylus (Fig. 5D, C). It also differs in the morphology of the G1, with the apical corneous process proportionally shorter (Fig. 6A, D), semicircular in cross-section (Fig. 6G), distinctly wider than the rest of the apical corneous process when seen from the dorsal view (Figs. 3F, 6A) and with a subterminal aperture in P. rahayuae n. sp., while it is longer (Fig. 6B), only slightly arched in cross-section (Fig. 6H), not much wider than the rest of the apical corneous process when seen from the dorsal view (Fig. 6B) and with a terminal aperture in P. anambas.
description: Published as part of Shahdadi, Adnan, Schubart, Christoph D. & Mendoza, Jose Christopher E., 2023, Phylogenetic evidence and morphological diagnosis for a new species of Parasesarma De Man, 1895 (Decapoda, Brachyura, Sesarmidae) from Sulawesi, Indonesia, pp. 567-576 in Zootaxa 5336 (4) on pages 568-574, DOI: 10.11646/zootaxa.5336.4.7, http://zenodo.org/record/8282237