Leptomithrax lowryi Forges & Ng 2023, sp. nov.
Creators: name: Forges, Bertrand Richer De
name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2023
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Majidae
Leptomithrax
Leptomithrax lowryi

description: Leptomithrax lowryi sp. nov.
urn:lsid:zoobank.org:act: 292CCDCA-480E-4EA0-8AE0-A1106D23CD9C
Figs 1–5
Holotype: MNHN-IU-2022-187, male (cl 40.7 mm, pcl 34.3 mm, cw 37.0 mm, pcw 30.7 mm), station DW 5238, east of Atoll de la Surprise, New Caledonia, 18°06.5'S 163°03.4'E, 254–274 m, coll. SPANBIOS cruise, N.O. “Alis”, 22 July 2021. Paratypes: MNHN-IU-2018-5013, 1 male (cl 35.6 mm, pcl 29.3 mm, cw 29.4 mm, pcw 24.2 mm), 1 subadult female (cl 17.1 mm, pcl 14.8 mm, cw 13.7 mm, pcw 12.1 mm) same data as holotype; MNHN-IU-2020-3639, 1 male (cl 28.0 mm, pcl 22.4 mm, cw 23.6 mm, pcw 17.7 mm), station DW 5171, south of Atoll Pelotas, New Caledonia, 19°01.4'S 163°26.8'E, 262–272 m, coll. SPANBIOS cruise, N.O. “Alis”, 8 July 2021; ZRC 2022.0045, 1 male (cl 32.3 mm, pcl 31.7 mm, cw 32.2 mm, pcw 27.5 mm), station DW 5207, east of Atoll de la Surprise, New Caledonia, 18°09'S 163°05.3'E, 239–248 m, coll. SPANBIOS cruise, N.O. “Alis”, 17 July 2021; ZRC 2022.0046, 1 female (cl 38.0 mm, pcl 30.8 mm, cw 30.9 mm, pcw 26.3 mm), 1 female (cl 38.1 mm, pcl 32.1 mm, cw 32.1 mm, pcw 26.2 mm), station DW 5207, east of Atoll de la Surprise, New Caledonia, 18°09'S 163°05.3'E, 239–248 m, coll. SPANBIOS cruise, N.O. “Alis”, 17 July 2021; MNHN-IU-2021-3746, 1 female (cl 30.1 mm, pcl 24.5 mm, cw 26.4 mm, pcw 20.2 mm), 1 juvenile, station DW5174, south of Atoll Pelotas, New Caledonia, 18°57.8'S 163°23.2'E, 320–342 m, coll. SPANBIOS cruise, N.O. “Alis”, 8 July 2021; MNHN-IU-2022-186, 1 male (cl 30.8 mm, pcl 21.9 mm, cw 25.0 mm, pcw 16.6 mm), 1 subadult female (cl 14.1 mm, cw 10.8 mm), station DW727, slope southwest of Dumbéa passage, New Caledonia, 22°48.03'S 167°29.03'E, 299–302 m, coll. BATHUS 2 cruise, N.O. “Alis”, 12 May 1993.
Diagnosis. Carapace very wide posteriorly, inflated medially; dorsal surface strongly granulous, anterior half gently convex. Pseudorostral spines divergent. Supraocular eave wide; intercalated spine narrow, distally blunt, almost totally closing gap between antorbital and postorbital spines; postorbital spine long, foliaceous, divided distally into 2 spines, proximal angle with distinct tooth. Basal antennal article surface almost flat, outer margin distinctly convex. Third maxilliped with junction of merus and ischium gently swollen; ischium with distinctly Y-shaped median furrow, anteroexternal angle forming large tooth with rounded tip. Ambulatory legs, especially meri, with smooth dorsal margin. Male thoracic sternites with lateral surfaces shallowly but distinctly excavated. Male telson subpentagonal. G1 slender, distal one-third curving outwards; distal part relatively long, gently sinuous.
Description. Carapace pyriform, very wide posteriorly; dorsal surface very granulous, anterior half gently convex; gastric and branchial regions distinct, separated by distinct grooves; carapace and pereiopods covered with scattered short setae, not obscuring surface or margins (Figs 2, 3A–C). Pseudorostral spines sharp, gently curved, diverging, cylindrical in cross-section, lateral margins without distinct spines or tubercles (Figs 1, 2, 3A–C). Proepistome with sharp, gently curved spine, visible in dorsal view (Figs 3B, C, 4C). Supraocular eave wide, forming sharp anterior and posterior angles, deeply convex above eye; intercalated spine narrow, distal part acute with proximal part subtruncate, almost totally closing gap between antorbital and postorbital spines with narrow basal fossae visible; postorbital spine long, foliaceous, divided distally into 2 short spines, proximal angle with distinct tooth (Figs 2, 3A, B, 4A, B). Carapace inflated medially, with granulated tubercles but no spine; posterior margin of carapace with 2 short sharp divergent spines; hepatic area with 2 strong spines directed outward; 4 lateral branchial spines, with posterolateral part armed with 3 sharp long spines, posteriormost one subdorsal in position, directed posteriorly and upwards, distinctly longer than other spines (Figs 2C, 3D, 4F). Basal antennal article wide, surface smooth, almost flat, completely fused with carapace, internal distal margin forming blunt tooth, outer margin distinctly convex, smooth; urinary article with subrectangular orifice; separated from postorbital spine by basal fossa (Fig. 4B); antenna deeply protected, far from orbit, flagellum long (Figs 3B, D, 4A–D). Eye short, protected by inner surface of postorbital tooth; cornea ovate, large, with small granule at distal tip (Fig. 4C–D). Epistome medially depressed with smooth surface (Fig. 4D). Epistome transversely rectangular; posterior margin with broad, subtruncate median plate, with deep median fissure; separated from lateral parts by deep V-shaped cleft (Fig. 4C, D).
Third maxilliped short, with smooth surface, bordered by setae on margin of merus; junction of merus and ischium gently swollen medially; ischium with distinctly Y-shaped median furrow, outer branch of furrow about three-quarters length of inner branch, anteroexternal angle with large tooth with rounded tip; merus short, anteroexternal angle auriculiform, distal median margin with rounded tooth, separated from inner part by deep cleft; exopod relatively slender, reaching to median part of merus, with long flagellum (Fig. 4D, E).
Chelipeds not elongate; merus short, dorsal margin lined with rounded and sharp granules, without distal spine; carpus short, proximal dorsal surface with granules, rest of surface smooth; chela slender, surfaces smooth; fingers shorter than palm, almost straight, cutting margins with denticles; proximal part of cutting margin of dactylus with low concavity, followed by low, wide tooth (Figs 2, 3D, 5B).
Ambulatory legs, especially meri, proportionately long; first leg longest, fourth leg shortest; merus subcylindrical, dorsal margin smooth, distal angle of dorsal margin angular but not spiniform or dentiform; propodus longer than dactylus; dactylus gently curved with corneous tip (Figs 2, 3D).
Thoracic sternites 1–4 completely fused; proximal part of sternite 4, median surface of sternites 5 and 6 with low granules; median longitudinal ridge on sternites 3 and 4 relatively low, with lateral surfaces shallowly but distinctly excavated; distal part of sternopleonal cavity demarcated by relatively sharp C-shaped ridge; part of sternite 8 exposed when male pleon closed (Fig. 5A).
Male pleon subrectangular in shape, with 6 free somites and telson; telson subpentagonal with convex distal margin; somite 3 widest, reaching coxae of last ambulatory legs; somite 4 trapezoidal; somites 5 and 6 rectangular; (Fig. 5A).
G1 slender, distal one-third curving outwards; distal part relatively long, gently sinuous, ventral margin lined with distinct spinules (Figs 5C–F, 6A–C). G2 short, ca. one-fifth length of G1; tip cup-like with very short flagellum (Fig. 6D).
Colour. Dorsal surfaces orange (Fig. 1).
Etymology. This species is named in honour of our friend and colleague James (Jim) Kenneth Lowry from the Australian Museum. A prolific taxonomist of peracarids, especially amphipods of the superfamily Lysianassoidea, he was also responsible for an important revision of the giant deep-sea isopods of the genus Bathynomus A. Milne-Edwards, 1879.
Remarks. Griffin & Tranter (1986: 208) divided Leptomithrax into several species groups, separated by various carapace and third maxilliped features. One group, with L. sternocostulatus and L. bifidus, has the distal part of the postorbital tooth truncate or bifid, the intercalated spine is mostly excluded from the rim of the incipient supraorbital margin, the junction of the ischium and merus of the third maxilliped is swollen, and the surfaces of the thoracic sternum and/or pleon are excavated. Griffin & Tranter (1986: 208) placed L. sinensis elsewhere as its third maxilliped and sternal conditions were not known, but Wong et al. (2018) showed it was close to L. bifidus and should also be in this group of species. Two other species, L. depressus and L. eldredgei also belong to this group.
Leptomithrax sternocostulatus can immediately be separated from other members of this group in that it only has three lateral branchial spines and the excavations on the male thoracic sternum and pleon are very deep with rims around the depressions; all the others have four lateral branchial teeth and the excavations on the ventral surface are distinctly shallower (cf. Grant & McCulloch, 1906: pl. 3 fig. 2; Poore, 2004: figs. 111b, c, 115p). Leptomithrax depressus is distinct in that the anterior one-third of the dorsal surface of the carapace is more flattened than any of the congeners and can also be separated from L. lowryi sp. nov. in having the male pseudorostral spines proportionately shorter and subparallel (Richer de Forges, 1993: fig. 7a, b) (versus long and distinctly diverging in L. lowryi sp. nov.; Fig. 2); the proximal angle of the postorbital tooth is demarcated by a low rounded lobe (Richer de Forges, 1993: fig. 7b) (versus a distinctly dentiform lobe in L. lowryi sp. nov.; Fig. 3A, B); the intercalated spine is short, triangular with a rounded tip (Richer de Forges, 1993: fig. 7b) (versus spine longer with a sharp distal part and a more truncate base in L. lowryi sp. nov.; Fig. 3A, B); the fourth subdorsal branchial spine is stouter and slightly longer than the third spine (Richer de Forges, 1993: fig. 7b) (versus spine is distinctly longer and more slender in L. lowryi sp. nov.; Figs 2, 3A); the ambulatory legs, in particular the meri, are proportionately shorter (Richer de Forges, 1993: fig. 7a) than in L. lowryi sp. nov. (Fig. 2); the surface of the merus of the ambulatory legs, especially upper surface, is coarsely granular and uneven (Richer de Forges, 1993: fig. 7b) (versus smooth in L. lowryi sp. nov.; Fig. 2); and the distal quarter of the G1 is gently curved (Richer de Forges, 1993: fig. 7c) (versus distal part of the G1 is sinuous in L. lowryi sp. nov.; Figs 5C–F, 6A–C).
Leptomithrax eldredgei can be separated from L. lowryi sp. nov. by the more slender carapace and the proportionally shorter lateral branchial spines (compare Richer de Forges & Ng, 2015: fig. 1A with Figs 2, 3A); the male pseudorostral spines are proportionately shorter and subparallel (Richer de Forges & Ng, 2015: fig. 1A, D) (versus long and distinctly diverging in L. lowryi sp. nov.; Fig. 2); the postorbital tooth appears foliaceous and almost entire, with the distal angle marked by a low bifurcation and the posterior angle broad and rounded (Richer de Forges & Ng, 2015: fig. 1A) (versus distal and proximal parts separated by deep cleft, the proximal angle marked by a distinct tooth in L. lowryi sp. nov.; Fig. 3A, B); the submedian sulcus on ischium of third maxilliped is almost entire and the anteroexternal angle has a sharp tooth (Richer de Forges & Ng, 2015: fig. 1C) (versus the sulcus on the ischium is Y-shaped with the anteroexternal angle rounded in L. lowryi sp. nov.; Fig. 4E); and the distal part of the G1 is gently curved and proportionately shorter (Richer de Forges & Ng, 2015: fig. 2) (versus distal part of the G1 is sinuous in L. lowryi sp. nov.; Figs 5C–F, 6A–C).
The morphology of Leptomithrax lowryi sp. nov. appears to be closest to two east Asian species, L. bifidus Ortmann, 1893 and L. sinensis Rathbun, 1916 (Figs 7–9). The identity of L. sinensis was clarified by Richer de Forges & Ng (2015) from the type which is a dried carapace; with Wong et al. (2018) redescribing the species from fresh material from Taiwan and Japan and comparing it at length with L. bifidus. Leptomithrax lowryi sp. nov. differs from the two species in that its carapace is proportionately wider posteriorly (Figs 2, 3A) than in L. bifidus and L. sinensis (Fig. 7A–D); the posterolateral spines are relatively stout (Fig. 3A) (versus more slender in L. bifidus and L. sinensis, Fig. 7B, D); the intercalated spine is blunt (Fig. 3A, B) (versus sharp in L. bifidus and L. sinensis, Fig. 8E, F); the pseudorostral spines are less curved and diverging (Figs 2, 3A) (versus more curved and clearly diverging in L. bifidus and L. sinensis, Fig. 7B, D); the deep furrow on the ischium of the third maxilliped is distinctly Y-shaped with the outer branch about three-quarters the length of the inner one (Fig. 4D, E) (versus furrow weakly Y-shaped with the outer branch less than half the length of the inner one in L. sinensis and L. bifidus, Fig. 8A, B, E, F); the surface of the basal antennal article is almost flat (Fig. 4B–D) (versus gently depressed in L. sinensis and L. bifidus, Fig. 8E, F); the outer margin of the basal antennal article is distinctly convex and smooth (Fig. 4B–D) (versus almost straight, gently convex and may be lined with granules in L. sinensis and L. bifidus, Fig. 7E, F); and the median longitudinal ridge on fused male thoracic sternites 3 and 4 is relatively low, with the lateral surfaces gently depressed (Fig. 5A) (versus with median longitudinal ridge high, separating the two deep lateral depressions in L. sinensis and L. bifidus, Fig. 8C, D). The telson of the male of L. lowryi sp. nov. resembles that of L. sinensis, being subquadrate-subpentagonal in shape (Figs 5A, 8D), whereas that of L. bifidus is distinctly more triangular (Fig. 8C). The G1 of L. lowryi sp. nov. is distinctly different from that of L. bifidus in that the distal part is sinuous rather than gently curved (Figs 5C–F, 6A–C versus Fig. 9A–C). The G1 of L. lowryi sp. nov. is most similar to L. sinensis except that the distal spinous part is proportionately longer in the former species (Fig. 6A–C versus Fig. 9E–G).
It is noteworthy that L. lowryi sp. nov. from New Caledonia is morphologically closest to two East Asian species, L. bifidus and L. sinensis, rather than to taxa from Australia, viz. L. tuberculatus, L. sternomaculatus and L. depressus (cf. Griffin, 1966; Richer de Forges, 1993; Poore et al., 2008).
description: Published as part of Forges, Bertrand Richer De & Ng, Peter K. L., 2023, A New Species of Spider Crab of the Genus Leptomithrax Miers, 1876 (Crustacea: Brachyura: Majidae) from New Caledonia, pp. 535-546 in Records of the Australian Museum (Rec. Aust. Mus.) (Rec. Aust. Mus.) 75 (4) on pages 536-545, DOI: 10.3853/j.2201-4349.75.2023.1891, http://zenodo.org/record/10413594