Flabellamon Ng, 1996

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 : 435-436

publication ID	https://doi.org/ 10.11646/zootaxa.5476.1.32
publication LSID	lsid:zoobank.org:pub:078CE548-C895-4F3F-8965-66AB38C7388E
DOI	https://doi.org/10.5281/zenodo.12681499
persistent identifier	https://treatment.plazi.org/id/03B48782-FFD9-B863-0186-F84812FAF893
treatment provided by	Plazi
scientific name	Flabellamon Ng, 1996
status

Treatment

Genus Flabellamon Ng, 1996 View in CoL

Type species. Flabellamon pretzmanni Ng, 1996 View in CoL , by original designation (now a junior subjective synonym of Potamon kuehnelti Pretzmann, 1963 ).

Diagnosis. Carapace transversely sub-ovate, low; epigastric cristae anterior to postorbital cristae; postorbital cristae sharp, well developed, confluent with epibranchial teeth; epibranchial tooth well-developed, separated from external orbital tooth by deep, broad V-shaped cleft; external orbital tooth well-developed, triangular, with lateral margin longer than mesial margin; frontal and postorbital regions relatively narrow. Exopod of third maxilliped with well-developed flagellum, not reaching or exceeding width of merus. Ambulatory legs not elongated. Male sternopleonal cavitiy reaching imaginary line joining anterior edges of bases of chelipeds. G1 relatively short, stout, distinctly sinuous; terminal segment almost straight, short, with well-developed dorsal flap; groove for G2 marginal. G2 longer than G1, with long terminal segment which is shorter than subterminal segment.

Remarks. Flabellamon Ng, 1996 , is easily differentiated from all other potamid genera by the following suite of characters: narrow frontal and postorbital regions; sharp postorbital cristae, confluent with the well-developed epibranchial teeth; well-developed and acute external orbital tooth, separated from epibranchial tooth by deep Vshaped cleft; flagellum present on the third maxilliped exopod; male sternopleonal cavity reaching imaginary line joining the anterior part of the cheliped coxae; and a relatively short, stout and sinuous G1, with a well-developed dorsal flap on the distal part of the terminal segment.

Flabellamon most closely resembles Stelomon Yeo & Naiyanetr, 2000 [type species: Potamon kanchanaburiense Naiyanetr, 1992 ] in carapace physiognomy, sharing the following suite of characters: relatively low, flat carapace; narrow orbital region; weakly rugose to smooth regions behind the epigastric and postorbital cristae; sharp postorbital cristae, which are separated from the epigastric cristae by distinct grooves but confluent with the epibranchial teeth; well developed, tall and acute external orbital tooth; and third maxilliped with long exopod with well-developed flagellum ( Figs. 1 View FIGURE 1 , 3F View FIGURE 3 , 4A–C View FIGURE 4 ; cf. Ng 1996: figs. 1, 2; Yeo & Naiyanetr 2000: figs. 1, 2A, 3, 4, 5A, 6, 7A; Takeda et al. 2019: fig. 1). Nevertheless, Flabellamon can be clearly distinguished still from Stelomon by differences in G1 morphology: G1 subterminal segment relatively stouter and strongly tapering towards distal end ( Figs. 3A–D View FIGURE 3 , 5 View FIGURE 5 ; cf. Ng 1996: figs. 3A, B; Takeda et al. 2019: fig. 3A) (vs. G1 subterminal segment relatively more slender, gently tapering towards distal end; cf. Yeo & Naiyanetr 2000: figs. 2B, D, 5B, C, 7B, C); and G1 terminal segment not twisted along longitudinal axis, straight, with distinct, tall dorsal flap ( Figs. 3A–D View FIGURE 3 , 5 View FIGURE 5 , E; cf. Ng 1996: figs. 3A, B; Takeda et al. 2019: fig. 3A) (vs. G1 terminal segment distinctly twisted along longitudinal axis, without dorsal flap; cf. Yeo & Naiyanetr 2000: figs. 2C, 2E–H, 5D, E, 7D, E). The G1 morphology of Flabellamon most closely resembles that of Takpotamon Brandis, 2002 (type species: Potamon maesotense Naiyanetr, 1992 ) and Thampramon Ng & Vidthayanon, 2013 (type species: Thampramon tonvuthi Ng & Vidthayanon, 2013 ); however, they can still be distinguished by clear differences in external morphology as well as G1 morphology. Flabellamon can be distinguished from Takpotamon and Thampramon by the following differences: low carapace ( Figs. 1C View FIGURE 1 , 4C View FIGURE 4 ; cf. Takeda et al. 2019: fig. 1C) (vs. carapace high in Takpotamon ; cf. Ng & Naiyanetr 1993: fig. 2B; Naiyanetr 2001: fig. 1A); carapace weakly rugose particularly at branchial region ( Figs. 1A View FIGURE 1 , 4A View FIGURE 4 ; cf. Ng 1996: figs. 1, 2A; Takeda et al. 2019: fig. 1A) (vs. carapace surface relatively smooth overall for Thampramon ; cf. Ng & Vidthayanon 2013: fig. 2); short, stout ambulatory legs ( Fig. 1A View FIGURE 1 ; cf. Takeda et al. 2019: fig. 1A) (vs. distinctly elongated ambulatory legs; cf. Naiyanetr 2001: pl. 1; Ng & Vidthayanon 2013: fig. 2); external orbital tooth relatively larger, taller ( Figs. 1A View FIGURE 1 , 4A View FIGURE 4 ; cf. Ng 1996: figs. 1, 2A; Takeda et al. 2019: figs. 1A, 2B) (vs. external orbital tooth relatively smaller, shorter in Takpotamon ; cf. Ng & Naiyanetr 1993: fig. 2A; Naiyanetr 2001: fig. 1B); cleft separating external orbital tooth and epibranchial tooth deep and broad ( Figs. 1A View FIGURE 1 , 4A View FIGURE 4 ; cf. Ng 1996: figs. 1, 2A; Takeda et al. 2019: fig. 1A) (vs. cleft separating external orbital tooth and epibranchial tooth shallow and narrow in Takpotamon ; cf. Ng & Naiyanetr 1993: fig. 2A; Naiyanetr 2001: fig. 1B); epigastric cristae clearly separated from postorbital cristae by distinct deep groove ( Figs. 1A View FIGURE 1 , 4A View FIGURE 4 ; cf. Ng 1996: fig. 2A; Takeda et al. 2019: fig. 1A) (vs. epigastric cristae confluent or almost confluent with postorbital cristae; cf. Ng & Naiyanetr 1993: fig. 2A; Naiyanetr 2001: fig. 1B; Ng & Vidthayanon 2013: fig. 2A); cervical grooves distinct but shallow, broad ( Figs. 1A View FIGURE 1 , 4A View FIGURE 4 ; cf. Ng 1996: fig. 1; Takeda et al. 2019: fig. 1A) (vs. cervical grooves not distinct; cf. Ng & Naiyanetr 1993: fig. 2A; Ng & Vidthayanon 2013: fig. 2); male telson narrowly triangular, lateral margins concave ( Figs. 2A View FIGURE 2 , 4B View FIGURE 4 ; cf. Ng 1996: fig. 1; Takeda et al. 2019: fig. 1D) (vs. male telson broadly triangular, lateral margin relatively straight or gently convex; cf. Ng & Naiyanetr 1993: fig. 2C; Naiyanetr 2001: fig. 1C; Ng & Vidthayanon 2013: fig. 4); G1 relatively more stouter, sinuous, with the subterminal segment abruptly tapering towards distal end ( Figs. 3A–D View FIGURE 3 , 5 View FIGURE 5 ; cf. Ng 1996: fig. 3A, B; Takeda et al. 2019: fig. 3A) (vs. G1 relatively more slender, almost straight, with the subterminal gradually tapering towards distal end; cf. Ng & Naiyanetr 1993: fig. 35B, C; Naiyanetr 2001: fig. 1F; Ng & Vidthayanon 2013: fig. 7C, D); and dorsal flap of G1 terminal segment without cleft ( Figs. 3A–D View FIGURE 3 , 5 View FIGURE 5 ; cf. Ng 1996: fig. 3A, B; Takeda et al. 2019: fig. 3A, B) (vs. dorsal flap of G1 terminal segment with distinct cleft on distal part in Thampramon ; cf. Ng & Vidthayanon 2013: fig. 7C, D).