Latopilumnus ajmali Ng, Prema & Ravichandran, 2024, n. sp.
Creators: name: Ng, Peter K. L.
name: Prema, Mani
name: Ravichandran, Samuthirapandian
Publisher: name: Zenodo
Year: 2024
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Pilumnidae
Latopilumnus
Latopilumnus ajmali

description: Latopilumnus ajmali n. sp.
(Figs. 1B, 5–7)
Type material. Holotype: female (cw 5.2 mm, cl 3.6 mm) (CASAU-CR-2020-1023), Mankudy fish landing centre, Kanyakumari district, Kanyakumari district, Tamil Nadu, southern India, Southeastern Arabian Sea, 8°05′29.8′′N, 77°29′02.9′′E, 50–60 m, in reef sponge, coll. M. Prema, 12 October 2020.
Etymology. The species is named in honor of the eminent carcinologist, the late Professor Syed Ajmal Khan, from the Centre of Advanced Study in Marine Biology, Annamalai University, who passed away in October 2022.
Diagnosis. Carapace transversely hexagonal, broader than long, regions not distinct; surface covered with very short, dense setae which obscures surface and partially margins, no plumose setae, with scattered long simple setae mostly on frontal margin and pereopods; dorsal surface with relatively scattered small rounded granules on anterolateral surface, low striae on posterolateral surface (Figs. 5B, 7A); frontal margin protruding anteriorly, distinctly bilobed, separated by V-shaped notch medially, margin gently convex, lined with numerous small granules; lateral frontal lobe low, separated from frontal lobe by small notch, confluent with granulated, entire supraorbital margin (Figs. 5B, 7A); suborbital margin granulated, suborbital tooth low, not distinctly produced, barely visible in dorsal view (Fig. 5B–D); external orbital tooth broad, proximal angle short; anterolateral margin with 3 distinct low teeth, margins lined with granules, second tooth largest, third smallest, directed obliquely (Figs. 5B, 7A); suborbital, sub-branchial and pterygostomial regions finely granular (Fig. 5C, D); median lobe of posterior margin of epistome produced, triangular (Figs. 5C, 7C); merus of third maxilliped quadrate, anteroexternal angle rounded (Fig. 7B); chelipeds asymmetrical; inner margin of merus lined with teeth; outer surface of carpus with numerous granules, inner distal angle produced as distinct tooth, lined with granules; outer surface of larger palm covered with rounded granules on upper half; outer surface of smaller chela covered with granules and tubercles (Figs. 5A, 6B–E); P2–P4 merus with 6 or 7 obvious sharp teeth on extensor margin, becoming larger distally, proximal ones small to barely visible (teeth on P5 much smaller); flexor margin unarmed; P2–P5 carpus and propodus with 2 longitudinal rows of sharp granules (those on P5 relatively smaller) (Figs. 5A, 6F, G).
Colouration. In the fresh specimen of L. ajmali n. sp., the carapace, cheliped and ambulatory legs are orange, with fine dark red spots on the frontal surfaces; and covered by a dense, short tomentum; with the fingers of the chelae pale white to pale yellow (Fig. 1B).
Remarks. Latopilumnus ajmali n. sp. can be separated from congeners by the carapace and pereiopods being covered with a relatively dense coat of short setae with only scattered simple long setae (mostly long the front) and without plumose setae (Fig. 5A, B, D). These short setae, however, are not sufficiently dense to form thick coat that completely obscures the surface and margins. In addition, the dorsal carapace surface is almost smooth except for scattered granules on the anterolateral and low striae on the posterolateral surfaces, with the regions poorly demarcated (Fig. 5A, B). In congeners, there are always tufts of long plumose setae (termed club-shaped setae by some authors) along the anterior parts of the carapace and/or pereiopods, and the regions of the carapace are often distinct, with numerous and/or prominent tubercles and granules, especially on the lateral surfaces.
Compared to L. ajmali n. sp., L. truncatospinosus has the anterior part of the carapace relatively more granulated (Ng & Clark 2008: fig. 1A) (vs. anterolateral surface relatively scattered small rounded granules in L. ajmali n. sp.; Figs. 5B, 7A); there are long setae on the gastric and branchial regions (Ng & Clark, 2008: fig. 1A) (vs. long simple setae present mostly on the frontal margin of the carapace in L. ajmali n. sp.; Fig. 5A, B); the last anterolateral tooth is directed obliquely anteriorly (Ng & Clark 2008: fig. 1A) (vs. directed more laterally in L. ajmali n. sp.; Figs. 5B, 7A); there is a large tubercle on the anterolateral surface (Ng & Clark 2008: fig. 1A) (vs. anterolateral surface only lined with granules in L. ajmali n. sp.; Figs. 5B, 7A); the suborbital tooth is strongly produced and visible in dorsal view (Ng & Clark 2008: fig. 1A) (vs. suborbital tooth not distinctly produced and barely visible in dorsal view in L. ajmali n. sp.; Figs. 5B, 7A); and the outer surface of the chela and carpus are uniformly covered with large coneshaped tubercles (Ng & Clark 2008: fig. 1C, D) (vs. the outer surface of the carpus with numerus with granules, larger palm with rounded granules, and smaller palm with granules and tubercles in L. ajmali n. sp.; Figs. 6B–E).
Latopilumnus malardi differs from L. ajmali n. sp. in having the anterior part of the carapace relatively more granulated (Ng & Clark 2008: figs. 4A, 5A) (vs. anterolateral surface relatively scattered small rounded granules in L. ajmali n. sp.; Figs. 5A, B, 7); there are long setae on the gastric and branchial regions (Ng & Clark 2008: fig. 4A) (vs. the long simple setae mostly occur on the frontal margin of the carapace in L. ajmali n. sp.; Fig. 5A); the anterolateral teeth are relatively lower are more lobiform (Ng & Clark 2008: figs. 4A, 5A) (vs. larger and clearly dentiform in L. ajmali n. sp.; Figs. 5B, 7A); the suborbital tooth is more produced and visible in dorsal view (Ng & Clark 2008: figs. 4A, 5A) (vs. suborbital tooth is not distinctly produced and barely visible in dorsal view in L. ajmali n. sp.; Figs. 5B, 7A); and the longitudinal rows of granules on the ambulatory carpus and propodus are low (Ng & Clark 2008: fig. 4C) (vs. granules larger and more prominent in L. ajmali n. sp.; Fig. 6F, G).
Latopilumnus guinotae can easily be distinguished from L. ajmali n. sp. as it has longer and denser (including plumose setae) which gives the species a more setose appearance (Deb 1987: pl. 13 fig. 3) (vs. less setose and only scattered setae in L. ajmali n. sp.; Figs. 5A, B, 7A); the anterolateral teeth are erect spines, with the outer surface of the chelae smooth (Deb 1987: pl. 13 fig. 3) (vs. anterolateral margin are armed with distinct teeth and the outer surface of the chela have large tubercles in L. ajmali n. sp.; Figs. 5A, B, 6B–E, 7A); the ambulatory meri are not armed (Deb 1987: 311, pl. 13 fig. 3) (vs. serrate in L. ajmali n. sp.; Fig. 6F, G); and the ambulatory carpus and propodus are not lined with rows of granules (Deb 1987: 311, pl. 13 fig. 3) (vs. with distinct granules in L. ajmali n. sp.; Fig. 6F, G).
Having the lateral margins of the anterolateral teeth granulated or serrated is a character also present in some species of Pilumnus, notably P. longicornis Hilgendorf, 1879, and its allies, and most of these species also have prominent spines on the P2–P5 merus (cf. Hilgendorf 1879: pl. 1 figs. 8, 9; Forest & Guinot 1961: pl. 17 fig. 3). These species, however, all have a well-developed lateral lobule which is demarcated from the frontal lobes and supraorbital margin and the P2–P5 carpus and propodus are not armed with rows of granules.
Latopilumnus ajmali n. sp., superficially resembles Pilumnus tantulus Rathbun, 1923 (from Queensland) in its general appearance, although the latter species has apparently more long setae. This species was synonymised under P. longicornis Hilgendorf, 1879 (see Balss 1933: 15; Takeda & Miyake 1968: 54) but its carapace form is actually quite different and the P2–P5 are distinctly shorter and is now regarded as a valid taxon (see Ng 1988: 295). Pilumnus tantulus, differs from L. ajmali in having the lateral lobule of front relatively more developed (Rathbun 1923: pl. 25 fig. 1) (vs. lateral lobule very low in L. ajmali n. sp.; Figs. 5B, 7A); the anterolateral teeth are distinctly longer and more developed (Rathbun 1923: pl. 25 fig. 1) (vs. anterolateral teeth lower in L. ajmali n. sp.; Figs. 5B, 7A); the outer surface of the major chela is smooth (Rathbun 1923: pl. 25 fig. 2) (vs. covered with tubercles in L. ajmali n. sp.; Figs. 6B–E); and the P2–P5 carpus and propodus are not lined with sharp granules (Rathbun 1923: pl. 25 fig. 1) (vs. lined with granules in L. ajmali n. sp.; Fig. 6F, G).
Distribution. Only known from the type locality.
description: Published as part of Ng, Peter K. L., Prema, Mani & Ravichandran, Samuthirapandian, 2024, Descriptions of new and rare crabs associated with coral rubble and sponges from Kanyakumari, southeastern Arabian Sea, southern India (Decapoda: Brachyura: Epialtidae and Pilumnidae), pp. 325-341 in Zootaxa 5476 (1) on pages 331-334, DOI: 10.11646/zootaxa.5476.1.26, http://zenodo.org/record/12681830