Leptarma dispersum Shahdadi & Schubart 2020, n. sp.
Creators: name: Shahdadi, Adnan
name: Schubart, Christoph D.
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Sesarmidae
Leptarma
Leptarma dispersum

description: Leptarma dispersum n. sp.
(Figs. 2, 3, 7A, 10A)
urn:lsid:zoobank.org:act: 359A7FDC-55A8-4A7B-868B-00FD88F15EE7
Parasesarma lenzii — Poupin et al. (2012: 13, Fig. 9A); not Parasesarma lenzii (De Man, 1895).
Material examined. Holotype: male (12.2×10.1) (MNHN-IU-2012-660), Mozambique Channel, Europa Island, coll. Poupin J., Gravier-Bonnet N., Zubia M., Tisné N., 11.Nov.2011 (Biodiversité, Ressources et Conservation des Récifs Coralliens des Îles Éparses (BIORECIFE) program, station 14) (see Poupin et al. 2012).
Diagnosis. Carapace slightly broader than long, front deflexed, slightly sinuous in dorsal view, median postfrontal lobes slightly wider than lateral ones, carapace lateral margin almost straight; eye with eyestalk short, stout, wider than long, corneal part slightly wider; male chela large and robust, upper surface of palm with one oblique pectinated crest, dorsal surface of dactylus bearing 12 low, transversely oval, asymmetric tubercles, with longer distal slope, proximal tubercles positioned at middle part of upper face of palm; ambulatory legs flattened dorsoventrally, long, third pair (P4) longest, total length (ischium-dactylus) ca. 2.0 times carapace width; Male pleon triangular, somite 2 medially longer than lateral edges; G1 long, straight, apical corneous process long, tip rounded, bent at angle of about 50° to vertical axis, aperture subterminal.
Description. Carapace subrectangular to slightly trapezoidal, slightly broader than long (cw/cl = 1.21), greatest width between exorbital angles; carapace surface smooth; front ca. 0.62 times carapace width, markedly deflexed, slightly sinuous in dorsal view; post-frontal lobes prominent, median lobes slightly wider than lateral ones, separated by shallow furrow; dorsal carapace regions well indicated, gastric region demarcated, cardiac region separated from intestinal region, lateral branchial ridges prominent; anterolateral margin with sharp exorbital angle, lateral margin almost straight, edged with row of short setae. Eye with eyestalk short, stout, wider than long, corneal part slightly wider (Figs. 2A, 3A).
Male chela large (palm length/cw = 0.54) (Fig. 2B), robust (palm width/length = 0.48) (Fig. 3B); merus with granulate dorsal border, no distinct subdistal spine, ventral border granulate, anterior border granulate, with distinct subdistal spine, accompanied by several spines distally, inner face smooth with longitudinal row of setae, anterior face smooth, outer face with rows of fine granules; upper surface of palm with 1 oblique pectinated crest and two rows of fine granules proximal to the crest, that is composed of 17 well developed teeth, and terminates at inner end in two granules and several granules on outer side (Fig. 3C, D); outer surface of palm with short rows of fine granules except for smooth, punctate fixed finger; inner surface of palm finely granular except area facing carpus and distal half of finger; no vertical ridge; both sides of palm with scattered tufts of setae; dactylus slightly curved downward and inward, dorsal surface bearing 12 low but distinct, transversely oval tubercles, distinct to tip, tubercles asymmetric, with distal slope longer, proximal tubercles positioned at middle part of upper face of palm; small pointed granules on inner side (Fig. 3C, D); scattered tufts of setae on inner side, cutting edge of both fingers with a series of variably sized teeth (Fig. 3B).
Ambulatory legs flattened dorso-ventrally, relatively long, third pair (P4) longest (Fig. 2), total length (ischiumdactylus) ca. 2.0 times carapace width, cluster of setae on coxae of P3, P4, tufts of long setae scattered along the legs, more on propodi and dactyli, merus of P4 ca. 2.37 times as long as wide, with anterior margin crenulated, propodus ca. 3.5 times as long as wide, dactylus ca. 0.67 times length of propodus.
Male pleon triangular (Figs. 2B, 3E), with rounded telson, slightly wider than long (basal width/length = 1.1), almost as long as somite 6; somite 6 longer than others; somites 4 and 5 trapezoidal, somite 3 widest, laterally convex, somite 2 medially longer than lateral edges (Fig. 3F).
G1 relatively long, straight; apical corneous process long, tip rounded, bent at angle of about 50° to vertical axis, arched in cross section, aperture subterminal (Fig. 3 G–J).
Female. No female specimen was examined.
Color. The specimen preserved in ethanol does not show any coloration, but according to Poupin et al. (2012: Fig. 9B, p. 22), the carapace seems brownish, ambulatory legs with scattered black stains dorsally and chelae with orange tip.
Habitat and distribution. The only specimen known for this species was collected from Europa Island, Grand Lagoon with mangroves and dead coral blocks (Poupin et al. 2012: st. 14 in Fig 1).
Etymology. The name is derived from the Latin verb “dispergere” (dispersed or scattered) and refer to its isolated position. It furthermore is a direct translation of the French name for the archipelago where it occurs: Îles Éparses.
Remarks. The specimen resembles L. lenzii in the morphology of chelar dactylar tubercles and G1 (Fig. 10A, B) and was first identified as such by Poupin et al. (2012). However, the specimen differ from L. lenzii in some morphological aspects. Most conspicuous is that the new species has proportionally longer ambulatory legs compared to L. lenzii, e.g. P4 (ischium-dactylus)/cw ca. 2.0 in the new species, while it is ca. 1.8 in L. lenzii; merus length/width ca. 2.3 in the new species, while this is ca. 2.1 in L. lenzii; propodus length/width ca. 3.5 in the new species, while it is ca. 2.9 in L. lenzii (Fig. 7A, B). The new species differs slightly from L. lenzii in G1 morphology by having an apical corneous process with wider tip (Fig. 10A, B).
The new species differs from the East African L. gazi in several morphological aspects as well as length of the ambulatory legs (Fig. 7A, C) and G1 morphology. P4 (ischium-dactylus) / cw ca. 2.0 in the new species, while it is ca. 1.9 in L. gazi. The G 1 in L. gazi is curved with a long apical corneous process, bent at an angle of about 10° with vertical axis, while the G 1 in the new species is straight, with wider apical corneous process, bent at an angle of about 50° with vertical axis (Fig. 10A, C).
Leptarma leptosoma is the more common East African congener in the area. This species is also different from the new species in many features. For example the new species has a wider carapace (cw/cl ca. 1.2) and a G1 with long apical corneous process, while L. leptosoma has a more squarish carapace (cw/cl less than 1.1) (Fig. 7A, D) and a G1 with short apical corneous process (Fig. 10A, D).
description: Published as part of Shahdadi, Adnan & Schubart, Christoph D., 2020, Two new species of Leptarma (Decapoda, Brachyura, Sesarmidae) from the Western Indian Ocean with notes on their phylogeny, pp. 439-456 in Zootaxa 4816 (4) on pages 442-445, DOI: 10.11646/zootaxa.4816.4.2, http://zenodo.org/record/3954577