Flabellamon mulayit, Tan & Yeo, 2024

Tan, Zhi Wan & Yeo, Darren C. J., 2024, On the genus Flabellamon Ng, 1996, with descriptions of two new species (Crustacea: Brachyura: Potamidae), Zootaxa 5476 (1), pp. 434-446 : 442-444

Flabellamon mulayit sp. nov.

( Figs. 4A–C , 5A–D )

Potamon atkinsonianum .— De Man 1898: 407 (part), pls. 4–5 fig. 6 (not Telphusa atkinsoniana Wood-Mason, 1871 ).

Potamon (Potamon) atkinsonianus . — Rathbun 1904: 271 (part) (not Telphusa atkinsoniana Wood-Mason, 1871 ).

Ranguna (Ranguna) turgidula .— Bott 1970: 164 (part) (not Potamon (Potamon) turgidulum Alcock, 1909 ).

Potamon “atkinsonianum ”.— Yeo & Ng 1999: 639 (part) (not Telphusa atkinsoniana Wood-Mason, 1871 ).

Type material. Holotype: male (31.3 × 24.3 mm), MSNG III 214 , Thagata, sul Monte Mooleyit [= Mount Mulayit ], Myanmar, coll. L. Fea, 1887 . Paratype: 1 female (25.4 × 18.8 mm), MSNG III 214 , same data as holotype .

Diagnosis. Carapace ( Fig. 4A ) transversely sub-ovate, low, broader than long (CW/CL ratio: 1.29); epigastric cristae well developed, not sharp, rugose, slightly anterior to postorbital cristae; postorbital cristae well developed, relatively sharp, rugose, confluent with epibranchial teeth epibranchial tooth blunt, broad, separated from external orbital tooth by deep broad V-shaped cleft; external orbital tooth lateral margin much longer than mesial margin. Third maxilliped exopod flagellum length subequal to width of merus. Male pleon ( Fig. 4B ) with sixth somite lateral margins gently convex. G1 ( Fig. 5C, D ) terminal segment appearing almost twisted longitudinally, with subdistal part of lateral margin truncate, dorsal flap high, subconical in appearance, narrow, with bluntly angular apex skewed towards proximal portion, gradually tapered distally, abruptly (almost perpendicularly) tapered proximally.

Etymology. The species is named after the type locality, Mount Mulayit. Used as noun in apposition.

Remarks. The present specimens were part of a mixed series of material identified by J. G. De Man as Potamon atkinsonianum ( Wood-Mason, 1871) ( De Man 1898; Rathbun 1904), a species now recognised as a member of the potamine genus Himalayapotamon ( Brandis 2001; Yeo & Ng 2004; Ng et al. 2008). De Man’s specimens differ from Himalayapotamon atkinsonianum ( Wood-Mason, 1871) sensu stricto in several external aspects including having broad, shallow cervical grooves with weakly rugose regions behind epigastric and postorbital cristae ( Figs. 1A , 4A ; cf. Pretzmann 1963: pl. 2 fig. 5; Ng 1996: figs. 1, 2A) (vs. deep, well developed cervical grooves and distinctly rugose regions behind epigastric and postorbital cristae; cf. Wood-Mason, 1871: 205, pl. 14 figs. 12–16; Alcock 1910: pl. 10, fig. 39; Brandis, 2001: fig. 3a). Bott (1970) later erroneously reassigned these specimens to Ranguna (Ranguna) turgidula (see earlier remarks for genus Flabellamon ). In fact, De Man’s material contains three taxa, viz., F. kuehnelti ( Pretzmann, 1963) , F. ngankee sp. nov. (see earlier) and the present undescribed taxon, herein named Flabellamon mulayit sp. nov. Flabellamon mulayit sp. nov. resembles F. kuehnelti in the large external orbital tooth with lateral margins much longer than mesial margins and G1 terminal segments with the subdistal part of the lateral margin appearing truncate ( Fig. 4A , 5A–D ; cf. Pretzmann 1963: pl. 2 fig. 5, 6; Ng 1996: figs. 1, 2A, 3A–D). Flabellamon mulayit , however, can be distinguished from F. kuehnelti by the following differences: blunt epibranchial tooth ( Fig. 4A ) (vs. sharp epibranchial tooth; cf. Pretzmann 1963: pl. 2 fig. 5; Ng 1996: 1, 2A); and G1 terminal segment appearing almost twisted longitudinally with dorsal flap being relatively higher and narrower, with a bluntly angular apex skewed towards the proximal portion ( Fig. 5A–D ) (versus G1 terminal segment not twisted longitudinally, with dorsal flap relatively lower and broader, with a broadly convex apex in the median portion; Fig. 5E ; cf. Pretzmann 1963: pl. 2 fig. 6; Ng 1996: fig. 3C, D).

Flabellamon mulayit sp. nov. shares the same type locality data (Monte Mooleyit = Mount Mulayit, Myanmar) as the poorly known species, Quadramon mooleyitense ( Rathbun, 1904) , which is represented by only one juvenile female holotype specimen (14.6 × 11.8 mm). Yeo & Ng (2007) had earlier recognised the distinctiveness of Potamon (Potamon) mooleyitense Rathbun, 1904 , and established Quadramon Yeo & Ng, 2007 , [type species: Quadramon aborense (Kemp, 1913) ], as a separate genus for it. Quadramon mooleyitense can be easily separated from Flabellamon mulayit sp. nov. by the following characters it possesses: very small, low, external orbital tooth ( Fig. 4D ) (vs. large, well developed external orbital tooth, Fig. 4A ); small, sharp epibranchial tooth, separated from external orbital tooth by shallow, narrow, cleft ( Fig. 4D ) (versus large, blunt epibranchial tooth, separated from external orbital tooth by deep, broad, cleft; Fig. 4A ); and postorbital cristae not sharp, broken up into rugae, not confluent with epibranchial teeth ( Fig. 4D ) (versus postorbital cristae sharp, entire, confluent with epibranchial teeth; Fig. 4A ). These characters are not known to vary greatly with size or age related, within a species.

Distribution. Myanmar: Thagata, sul Monte Mooleyit (= present day Mount Mulayit)

Figures

FIGURE 1. Flabellamon ngankee sp. nov., male holotype, 37.5 × 28.8 mm, ZRC 2024.0272: A, dorsal view; B, ventral view; C, frontal view; D, buccal cavity and third maxillipeds; E, minor chela (lateral view); F, major chela (lateral view).

FIGURE 4. A–C, Flabellamon mulayit sp. nov., male holotype, 31.3 × 24.3 mm, MSNG III 214; D, Quadramon mooleyitense (Rathbun, 1904) female, holotype, 14.6 × 11.8 mm, MSNG III 188. A, D, dorsal view; B, anterior thoracic sternum, pleon and telson; C, frontal view.

FIGURE 5. A–D, Flabellamon mulayit sp. nov., male holotype, 31.3 × 24.3 mm, MSNG III 214; E, Flabellamon kuehnelti (Pretzmann, 1963), male, 25.7 × 20.2 mm, NMB 19b. A, E, right G1 (dorsal view); B, right G1 (ventral view); C, terminal segment of right G1 (dorsal view); D, terminal segment of right G1 (ventral view). Scale bar; A, B, E = 2.0 mm; C, D = 1.0 mm.