Flabellamon kuehnelti (Pretzmann, 1963)

(Fig. 5E)

Potamon atkinsonianum. — De Man 1898: 407 (part) (not Telphusa atkinsoniana Wood-Mason, 1871).

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

Potamon kühnelti Pretzmann, 1963: 363, pl. 2.— Ng 1996: 1005.

Ranguna (Ranguna) turgidula.— Bott 1970: 164 (part), pl. 38 fig. 36, pl. 51 fig. 53 (not Potamon (Potamon) turgidulum Alcock, 1909).

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

Flabellamon kuehnelti. — Yeo & Ng 1999: 641.— Ng et al. 2008: 162.— Takeda et al. 2019: 90–91.

Flabellamon pretzmanni Ng, 1996: 1006, figs. 1–3.— Yeo & Ng 1999: 641.— Ng et al. 2008: 162.— Takeda et al. 2019: 90–91.

Material examined. Male (18.7 × 15.6 mm) (ZRC 1984.7035; exchange from NMB), Kokareet Hills [= present day Kawkareik], Tenasserim, Myanmar, coll. L. Fea, 1894 (holotype of Flabellamon pretzmanni Ng, 1996); 1 male (25.7 × 20.2 mm) (NMB 19 b), Kokareet, Tenasserim, Myanmar, coll. L. Fea, no date; 1 male (20.9 × 16.8 mm), 1 female (21.0 × 16.8 mm) (SMF 1761), Burma, Tenasserim, presented by Zoological Survey of India; 1 juvenile male (14.5 × 11.5 mm), 1 juvenile female (ZMA), Dal van de Houngdarau, May 1887; 1 male (19.8 × 15.5 mm), 1 female (ZMA), Meetan, Houng Darau, May 1887; 1 female (18.8 × 14.6 mm) (MSNG III 215), Meetan (sul Houngdarau), coll. L. Fea, May 1887; 4 juveniles (MSNG III 216), Valle del Houngdarau, coll. L. Fea, May 1887.

Diagnosis. Carapace (cf. Ng 1996: fig. 1) transversely sub-ovate, low, 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 distinct, well developed, sharp, narrowly triangular, separated from external orbital tooth by deep, broad V-shaped cleft; external orbital tooth well developed, acutely triangular, with lateral margin gently serrated, gently convex, cristate, longer than mesial margin, about 2 times length of mesial margin. Male pleon (cf. Ng 1996: fig. 2H) with sixth somite lateral margins gently convex. G1 (Fig. 5E; Ng 1996: fig. 3A–D) gently sinuous, stout; terminal segment clearly separated from subterminal segment, relatively stout, subconical, almost straight from base to tip, strongly bent outwards at an angle of ca. 35° from longitudinal axis of G1, tip tapered, with subdistal part of lateral margin truncate, with slight swelling on posterior part of outer margin, without longitudinal torsion, without swelling on inner margin, with well developed, high, broad, dorsal flap, rectangular in appearance, with broadly convex apex in median portion, abruptly tapered, almost perpendicularly, distally and proximally; subterminal segment relatively broad, not distinctly slender distally.

Remarks. Regarding the synonymy of Flabellamon pretzmanni Ng, 1996, under F. kuehnelti (Pretzmann, 1963), Ng (1996: 1008) did not in the first place examine the holotype of F. kuehnelti but indirectly contrasted the two species when he compared Pretzmann’s (1963: pl. 2 fig. 6) figure of the G1 of F. kuehnelti with a G1 from a specimen from Meelan (near Kokareet = present day Kawkareik) illustrated by Bott (1970: pl. 38 fig. 36), which he felt agreed “…extremely well with that of F. pretzmanni …” and was “…probably conspecific…” with it. Ng (1996: 1008) noted that the “…G1 of the specimen from Meelan (Bott 1970: pl. 38 fig. 36) differs from that of P. kuehnelti in being stouter, with the median part (where the structure begins to bend outwards) proportionately higher, and the subdistal part of the terminal segment appearing more truncate (versus smooth and gently tapering)…” However, in Pretzmann’s (1963: pl. 2 fig. 6) figure of the G1 of F. kuehnelti, the subdistal part of the terminal segment of F. kuehnelti appears truncate rather than “smooth and gently tapering” as suggested by Ng (1996) (Fig. 5E). The actual G1 structures of F. kuehnelti and F. pretzmanni therefore look almost identical, with the first difference most likely due to size-related variation, as the F. kuehnelti holotype (32.5 × 26.0 mm) is an adult specimen whereas the F. pretzmanni holotype (18.7 × 15.6 mm) is clearly a juvenile, with the G1 not fully developed. Externally, the epibranchial tooth is relatively more broadly triangular in the former than in the latter; and the lateral margins of the sixth male pleonal somite is distinctly convex in F. kuehnelti holotype (versus almost straight in F. pretzmanni holotype) (see Pretzmann 1963: pl. 2 figs. 5, 7; Ng 1996: figs. 1, 2A, H). These also appear to be due to size-related variation. The respective type localities, Meetun and Kokareet [= present day Kawkareik], are also fairly close to one another. As such, the two specimens are probably conspecific and F. pretzmanni should be a junior subjective synonym of F. kuehnelti, as regarded correctly by Ng et al. (2008) and Takeda et al. (2019). The specimen that Ng (1996: 1008) regarded as Flabellamon kuehnelti with a G1 terminal segment that is “smooth and gently tapering” is instead a new species and is described herein as F. ngankee sp. nov. Flabellamon kuehnelti is most similar to F. mulayit sp. nov. The two species, however, can be easily distinguished by clear differences in the G1 morphology (see later, remarks for Flabellamon mulayit sp. nov.).

Distribution. MYANMAR: Meetun (Pretzmann, 1963); Meelan, Tenasserim (Bott, 1970); Houangdarau, Meetun and Kawkareik.