Latopilumnus Türkay & Schuhmacher, 1985

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), Zootaxa 5476 (1), pp. 325-341 : 329-331

Genus Latopilumnus Türkay & Schuhmacher, 1985

Type species. Latopilumnus tubicolus Türkay & Schuhmacher, 1985 , by original designation.

Remarks. The low lateral lobule of the front is a character that would have placed Latopilumnus ajmali n. sp. in Parapilumnus Kossmann, 1877 , following the traditional classification (cf. Takeda & Miyake, 1969). Ng (2002) showed that Parapilumnus is not a pilumnid as the type species, Parapilumnus cristimanus (A. Milne-Edwards, 1873) is an acidopsid (see also Ng & Rahayu 2014). Ng (2002) nevertheless argued that the strength of the lateral lobule varies too much to be a useful generic character in any case and opted to just transfer the species then recognised in Parapilumnus to Pilumnus Leach, 1816 , s. lato. Ng & Clark (2008) subsequently redefined and revised Latopilumnus and included some species previously assigned to Parapilumnus .

The following characters of L. ajmali n. sp. are typical for species of Latopilumnus : lateral lobule of the front is relatively poorly demarcated, with the frontal margins almost confluent with the supraorbital margin ( Figs. 5B , 7A ), granulated margins on the anterolateral teeth giving it a serrate appearance ( Figs. 5B , 7A ), and presence of low serrations on the extensor margin of the P2–P5 merus, with the carpus and propodus distinctly lined with two rows of low, sharp granules (relatively lower in the P5) ( Fig. 6F, G ).

Six species of Latopilumnus are currently recognised: L. conicus Ng & Clark, 2008 , L. guinotae ( Deb, 1987) , L. malardi (De Man, 1914) , L. truncatospinosus (De Man, 1914) , L. tuberculosus ( Garth & Kim, 1983) , and L. tubicolus Türkay & Schuhmacher, 1985 (cf. Ng & Clark 2008). Of these, three are known from the Indian Ocean: L. guinotae (Andaman Islands), L. malardi ( Madagascar) and L. truncatospinosus ( Madagascar). The generic position of L. guinotae ( Deb, 1987) is unclear as it seems to lack most of the generic characters except for the low lateral lobule of the front, and it also appears to more pilose than congeners. Unfortunately, it was only described from one female (cw 7.0 mm, cl 5.0 mm) and the only figure provided is not very informative (cf. Deb 1987: 311, pl. 13 fig. 3). It will need to be re-examined to ascertain its precise generic position.

Some Latopilumnus species are known to be associated with barnacle clumps, dead corals and living hard corals ( Türkay & Schuhmacher, 1985). The only known specimen of the present new species, Latopilumnus ajmali n. sp. was found in sponges ( Fig. 1B ), but it is not clear if it is an obligate symbiont.

Figures

FIGURE 1. (A) Colony of Callyspongia diffusa (Ridley, 1884) (Callyspongiidae) collected by trawlers; (B) Latopilumnus ajmali n. sp., holotype female (cw 5.2 mm, cl 3.6 mm) (CASAU-CR-2020-1023), on callyspongiid sponge.

FIGURE 5. Latopilumnus ajmali n. sp., holotype female (cw 5.2 mm, cl 3.6 mm) (CASAU-CR-2020-1023), India: (A) overall habitus; (B) right side of carapace (denuded); (C) frontal view of cephalothporax; (D) antennules, antenna, orbit and epistome.

FIGURE 6. Latopilumnus ajmali n. sp., holotype female (cw 5.2 mm, cl 3.6 mm) (CASAU-CR-2020-1023), India: (A) anterior thoracic sternum and pleon; (B) dorsal view of left cheliped; (C) dorsal view of right cheliped; (D) outer view of right chela; (E) outer view of left chela; (F) right P4; G, right P5. D, E, and F, G, photographed to same magnification.

FIGURE 7. Latopilumnus ajmali n. sp., holotype female (cw 5.2 mm, cl 3.6 mm) (CASAU-CR-2020-1023), India: (A) right side of carapace (setae denuded); (B) left third maxilliped (denuded); (C) posterior margin of epistome. Scales: A = 1.0 mm; B, C = 0.5 mm.