Dromothelphusa Naiyanetr, 1992

Ng, Peter K. L. & Yeo, Darren C. J., 2023, Clarifying the identities of the Asian potamid genera Potamiscus Alcock, 1909, Ranguna Bott, 1966, and Dromothelphusa Naiyanetr, 1992 (Crustacea: Brachyura: Potamoidea), Raffles Bulletin of Zoology 71, pp. 632-657 : 647-648

publication ID	https://doi.org/ 10.26107/RBZ-2023-0048
publication LSID	lsid:zoobank.org:pub:19D286F4-F712-4645-93FF-1AC19A55EDE9
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scientific name	Dromothelphusa Naiyanetr, 1992
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Genus Dromothelphusa Naiyanetr, 1992 View in CoL

Demanietta (Dromothelphusa) Naiyanetr, 1992: 114 . Dromothelphusa View in CoL – Ng & Naiyanetr, 1993: 21, 45 (partim); Brandis,

2000: 95; Yeo & Ng, 2007: 307; Ng et al., 2008: 162.

Type species. Thelphusa longipes A. Milne-Edwards, 1869 View in CoL , by original designation.

Diagnosis. Carapace wider than long, relatively high, dorsal surface convex transversely and longitudinally in frontal view; epigastric cristae well developed, slightly anterior to postorbital cristae, more or less confluent with postorbital cristae, not clearly separated; postorbital cristae sharp, almost confluent with epibranchial tooth; regions behind epigastric and postorbital cristae almost smooth; frontal and postorbital regions relatively wide ( Figs. 10A–C View Fig , 11A–C, F View Fig ); external orbital angle triangular, outer margin longer than inner margin; epibranchial tooth low but distinct, separated by clear cleft; anterolateral margins cristate, serrated, gently convex; posterolateral margins gently converging posteriorly; branchial regions gently rugose ( Figs. 10A–C View Fig , 11A–C, F View Fig ). Antennular fossae longitudinally narrow, slit-like ( Fig. 11C View Fig ). Epistome posterior margin with acutely triangular median tooth, outer part gently sinuous ( Fig. 11C View Fig ). Ischium of third maxilliped relatively short, broadly rectangular, with distinct oblique median sulcus; exopod long, exceeding distal edge of ischium, with flagellum vestigial or absent in adults ( Figs. 11D View Fig , 12F–K View Fig ). Ambulatory legs not elongate, stout, with long, slender dactyli ( Figs. 10A View Fig , 11A, F View Fig , 12B, C View Fig ). Male anterior thoracic sternites relatively wider transversely; suture between anterior male thoracic sternites 2 and 3 visible but not deep, complete, reaching edge of sternum; no suture between anterior male thoracic sternites 3 and 4; male sternopleonal cavity reaching imaginary line joining midpoint of cheliped bases; tubercle of male press-button locking mechanism small, on posterior third of thoracic sternite 5 ( Figs. 11E View Fig , 12E View Fig ). Male pleon triangular; somite 6 trapezoidal, broader than long; male telson triangular with gently convex lateral margins ( Figs. 10A View Fig , 11E View Fig , 12D View Fig ). G1 subterminal segment relatively slender, terminal segment almost straight, subconical, with prominent dorsal flap on proximal half, groove for G2 marginal ( Fig. 14A–E View Fig ). G2 subequal in length to G1; distal segment about half length of basal segment; basal segment relatively narrow, with outer margin concave ( Fig. 14F View Fig ). Vulvae large, occupying ¾ anterior part of thoracic sternite 6, operculum present, sternal vulvar cover narrow, on posterior margin, opening obliquely inwards ( Fig. 12F View Fig ).

Remarks. Naiyanetr (1992) established Dromothelphusa (type species Thelphusa longipes A. Milne-Edwards, 1869 ) as a subgenus of Demanietta Bott, 1966 , to replace Ranguna Bott, 1966 , which Türkay & Naiyanetr (1987) had argued was a junior synonym of Potamiscus Alcock, 1909 (see Remarks for Potamiscus ). Dromothelphusa longipes certainly possesses a distinct dorsal flap in the G1 terminal segment, which Bott (1966) had used to define the genus Ranguna . Nonetheless, the exclusive use of the presence of a dorsal flap on the G1 as a generic diagnostic character was shown to be unreliable and Ranguna (sensu Bott, 1966; Naiyanetr, 1992) deemed heterogeneous ( Ng, 1988, 1990; Ng & Naiyanetr, 1993). This led to Ng & Naiyanetr (1993) redefining the genus Dromothelphusa , adding several carapace and male pleon characters to the genus diagnosis, and restricting the genus to only two species, D. longipes and D. phrae ( Naiyanetr, 1984) . Subsequently, five more species were added to Dromothelphusa , viz., D. namuan ( Naiyanetr, 1993) , D. nayung ( Naiyanetr, 1993) , D. sangwan Naiyanetr, 1997 , D. pealianoides ( Bott, 1966) , and D. prabang Yeo & Naiyanetr, 1999 (see Naiyanetr, 1993, 1994, 1997; Yeo & Naiyanetr, 1999).

Yeo & Ng (2007), however, showed that, while superficially similar, D. longipes differs from the rest of the Dromothelphusa species in several important morphological aspects of generic significance as well as in its disjunct distribution. This warranted a separate genus to be established for the remaining species, named Pupamon Yeo & Ng, 2007 , with Potamon namuan Naiyanetr, 1993 , as the type species. Pupamon is distinguished from Dromothelphusa s. str. by various carapace and G1 characters (see Yeo & Ng, 2007: 291). Dromothelphusa thus remains monotypic, with D. longipes being the sole member of the group, and the remaining species transferred to Pupamon (see Yeo & Ng, 2007: 291).

Dromothelphusa is superficially similar also to Eosamon Yeo & Ng, 2007 [type species: Potamon (Potamon) smithianum Kemp, 1923 ] and Aiyunamon Pan, Ng & Sun, 2022 [type species Eosamon daiae Zhang & Sun , in Zhang, Pan, Hao & Sun, 2020]. Dromothelphusa can be separated from Eosamon by the following characters: the epigastric cristae being more or less in line, and confluent, with the postorbital cristae ( Figs. 9B View Fig , 10B, C View Fig ) (versus epigastric cristae slightly anterior to, and faintly separated from postorbital cristae by short, indistinct groove); the postorbital cristae being smooth and confluent with the epibranchial tooth ( Figs. 9B View Fig , 10B, C View Fig ) (versus postorbital cristae cristate, not confluent with epibranchial tooth, breaking up into granules before reaching epibranchial tooth); the antennular fossae being slit-like ( Fig. 11C View Fig ) (versus antennular fossae subrectangular); the epibranchial tooth being low ( Figs. 9B View Fig , 10B, C View Fig ) (versus epibranchial tooth well developed, distinct); the anterolateral margins being gently but evenly serrated ( Figs. 9B View Fig , 10B, C View Fig ) (versus anterolateral margins unevenly serrated anteriorly); the exopod flagellum being vestigial or absent ( Fig. 11D View Fig ) (versus exopod flagellum well developed, exceeding merus width); the male sternopleonal cavity reaching an imaginary line joining the median part of the cheliped bases ( Fig. 11E View Fig ) (versus male sternopleonal cavity reaching the imaginary line joining the posterior edges of the cheliped bases); and the G1 terminal segment being straight ( Fig. 14A–E View Fig ) (versus G1 terminal segment gently curved outwards distally) (cf. Yeo & Ng, 2007: fig. 5; Pan et al., 2022: figs. 2E, 3E, 4E, 5E, F). The species in Aiyunamon were transferred from Eosamon only recently, and other than genetic data, most of the characters enumerated above for Eosamon also apply. The species in Aiyunamon can additionally be separated from Dromothelphusa in having the postorbital cristae rugose ( Pan et al., 2022: figs. 2A–D, 3A–D) (versus postorbital cristae relatively sharp); the epibranchial tooth being low and indistinct ( Pan et al., 2022: fig. 2A–D) (versus epibranchial tooth low but distinct); the G1 being curved, with the outer edge of the subterminal segment at the junction with the terminal segment concave (sometimes prominently so) ( Pan et al., 2022: fig. 5A–D, F–I) (versus G1 straight without any concavity on the subterminal segment); the G1 terminal segment possessing at most a low dorsal flap ( Pan et al., 2022: fig. 5A–D, F–I) (versus G1 dorsal flap large); and the vulva occupying about half the anterior part of the thoracic sternite 6 ( Pan et al., 2022: fig. 6A–D) (versus vulva distinctly larger and occupying ¾ of the anterior part of the thoracic sternite 6).