Capitamon, Pati & Peter & L., 2024

Pati, Sameer K., Mitra, Santanu & Ng, Peter K. L., 2024, Identity of the freshwater crab Indochinamon beieri (Pretzmann, 1966), with the description of a new genus and four new species from northeastern India (Decapoda, Brachyura, Potamidae), Zoosystema 46 (23), pp. 589-615 : 597-613

publication ID	https://doi.org/ 10.5252/zoosystema2024v46a23
publication LSID	lsid:zoobank.org:pub:9195A8AB-6FA8-4828-B8D1-DDEC94E99A6D
DOI	https://doi.org/10.5281/zenodo.13843758
persistent identifier	https://treatment.plazi.org/id/4E204ABF-5B88-4A72-A41E-44571B31469C
taxon LSID	lsid:zoobank.org:act:4E204ABF-5B88-4A72-A41E-44571B31469C
treatment provided by	Plazi
scientific name	Capitamon
status	gen. nov.

Treatment

Genus Capitamon n. gen.

( Figs 5 View FIG ; 6 View FIG ; 7 View FIG ; 8 View FIG ; 9 View FIG ; 10 View FIG ; 11 View FIG ; 12 View FIG ; 13 View FIG ; 14 View FIG ; 15 View FIG ; 16 View FIG ; 17 View FIG )

urn:lsid:zoobank.org:act:4E204ABF-5B88-4A72-A41E-44571B31469C

TYPE SPECIES. — Capitamon capitatum n. sp., by present designation; gender neuter.

DIAGNOSIS. — Carapace ovate, broader than long (CW/CL = 1.3- 1.4), relatively low ( CH /CW = 0.4-0.5); dorsal surface smooth except for epigastric cristae, postorbital cristae, epibranchial region and lateral surfaces; anterolateral margins cristate, with distinct granules; front with broad anterior margin (FW/CW = 0.3); epigastric cristae well-developed, rugose, anterior to postorbital cristae, separated from postorbital cristae by short groove; postorbital cristae well-developed, relatively sharp, not reaching lateral margin; external orbital angle triangular, with short outer margin; epibranchial tooth low, blunt; cervical grooves deep, narrow; epibranchial region with closely spaced granules; suborbital margin not joining with supraorbital margin; epistome posterior margin with well-developed, triangular median tooth ( Figs 5A, B View FIG ; 8A View FIG ; 9A, C View FIG ; 12A, B View FIG ; 15A, B View FIG ; see Pati et al. 2020: figs 1a; 2a, b). Antennae shorter than eye stalk; antennules long, folded in longitudinally broad fossae ( Figs 5B View FIG ; 9C View FIG ; 12B View FIG ; 15B View FIG ; see Pati et al. 2020: fig. 2b). Mandibular palp with three articles; terminal article simple, undivided ( Figs 6A View FIG ; 13A View FIG ; 16A View FIG ). First, second maxillipeds each with long flagellum on exopod ( Figs 6A View FIG ; 13A View FIG ; 16A View FIG ). Third maxilliped exopod slender, lacking flagellum or with relatively shorter flagellum (shorter than merus width) ( Figs 6B View FIG ; 9B View FIG ; 13B View FIG ; 16B View FIG ; see Pati et al. 2020: fig. 2c). Chelipeds rugose; carpus with prominent, sharp, triangular inner distal major tooth and low subbasal tooth ( Figs 5A View FIG ; 6C View FIG ; 8A View FIG ; 9E View FIG ; 12A View FIG ; 13C View FIG ; 15A View FIG ; 16C View FIG ; see Pati et al. 2020: fig. 1a). Ambulatory legs short, stout, with short setae on margins ( Figs 5A, C View FIG ; 8A View FIG ; 12A, C View FIG ; 15A, C View FIG ; see Pati et al. 2020: fig. 1a). Male s2/s3 deep, reaching lateral margins; male s3/ s4 indiscernible or with shallow groove; male s7/s8 interrupted by longitudinal medial groove of s7 and s8, lacking transverse ridge ( Figs 5C View FIG ; 6D View FIG ; 8B, E View FIG ; 12C View FIG ; 13D View FIG ; 15C View FIG ; 16D View FIG ; see Pati et al. 2020: figs 1b; 2e). Pleonal locking mechanism with prominent tubercle on posterior submedial part of s5 ( Figs 6D View FIG ; 8E View FIG ; 13D View FIG ; 16D View FIG ; see Pati et al. 2020: fig. 2e). Male sternopleonal cavity long, reaching to imaginary line joining medial part of cheliped coxae ( Figs 5C View FIG ; 6D View FIG ; 8B, E View FIG ; 12C View FIG ; 13D View FIG ; 15C View FIG ; 16D View FIG ; see Pati et al. 2020: figs 1b; 2e). Male pleon relatively broad; pleonal somite 6 trapezoidal, broader than long (proximal width c. 1.9-2.2 × medial length) ( Figs 5C View FIG ; 6E View FIG ; 8B View FIG ; 9D View FIG ; 12C View FIG ; 13E View FIG ; 15C View FIG ; 16E View FIG ; see Pati et al. 2020: figs 1b; 2d). Male telson triangular, slightly longer than pleonal somite 6 ( Figs 5C View FIG ; 6E View FIG ; 8B View FIG ; 9D View FIG ; 12C View FIG ; 13E View FIG ; 15C View FIG ; 16E View FIG ; see Pati et al. 2020: figs 1b; 2d). G1 moderately stout, with ultimate article strongly bent outwards at angle of about 60-110° from longitudinal axis, tip acute, not reaching pleonal locking structure; flexible zone large; ultimate article stout, short, c. 0.35 × combined length of flexible zone and penultimate article, with distinct, narrow to broadly triangular dorsal flap, entire structure resembling bird’s head in shape; penultimate article sinuous ( Figs 6D, F View FIG ; 7A View FIG , C-E; 8C, E; 10A, B, D; 11A, C-E; 13D, F; 14A, C-E; 16D, F; 17A, C-E; see Pati et al. 2020: figs 2e; 4a-d; 5a-c). G2 longer than G1; ultimate article long, c. 0.5-0.6 × length of penultimate article ( Figs 6F, G View FIG ; 7B, D View FIG ; 8C, D View FIG ; 10A, C View FIG ; 11B, D View FIG ; 13F, G View FIG ; 14B, D View FIG ; 16F, G View FIG ; 17B, D View FIG ; see Pati et al. 2020: figs 4a, e; 5a, d). Female pleon together with telson broadly ovate ( Figs 6H View FIG ; 13H View FIG ; 16H View FIG ; see Pati et al. 2020: fig. 3b). Vulvae on s6 positioned close to each other, ovate, opening mesially, longitudinally broad, large, occupying 0.5-0.6 × length of s6, touching s5/s6, almost reaching s4/s5 ( Figs 6I View FIG ; 13I View FIG ; 16I View FIG ; see Pati et al. 2020: fig. 3c).

ETYMOLOGY. — All the known congeners of the new genus have an ultimate article of the male first gonopod that resembles a bird’s head. The genus name is therefore derived from caput, Latin for head, in arbitrary combination with the genus name Potamon . The gender of the generic name is neuter.

GEOGRAPHICAL DISTRIBUTION. — Capitamon n. gen. is currently known from northeastern India, with its nominal species recorded from Arunachal Pradesh, Manipur, Mizoram and Nagaland states ( Fig. 1 View FIG ).

REMARKS

Capitamon n. gen. is undoubtedly a potamiscine genus (sensu Yeo & Ng 2004), with the s7/s8 being interrupted by the longitudinal medial groove of s7 and s8, and lacking a transverse ridge ( Figs 6D View FIG ; 8E View FIG ; 13D View FIG ; 16D View FIG ; see Pati et al. 2020: fig. 2e). Capitamon n. gen. can be differentiated from other potamiscine genera by the flagellum on the third maxilliped exopod being relatively shorter (shorter than the width of the merus) or altogether absent, and significantly, the “bird’s head-like” ultimate article of the G1, which is short, relatively stout, strongly bent outwards at an angle of about 60-110° from longitudinal axis of the G1 and possesses a distinct dorsal flap ( Figs 6F View FIG ; 7A View FIG , C-E; 8C; 10A, B, D; 11A, C-E; 13F; 14A, C-E; 16F; 17A, C-E; see Pati et al. 2020: figs 4a-d; 5a-c). As compared to that of Capitamon n. gen., the flagellum on the third maxilliped exopod is relatively longer (equal to or longer than the width of the merus), and the dorsal flap on the G1 ultimate article is absent or relatively low in Indochinamon View in CoL (cf. Ng & Win Mar 2018). The well-developed epigastric and postorbital cristae of Capitamon n. gen. ( Figs 5A View FIG ; 8A View FIG ; 9A View FIG ; 12A View FIG ; 15A View FIG ; see Pati et al. 2020: figs 1a; 2a) are also useful to distinguish it from other potamiscine genera with similar conditions of the G1 and the flagellum on the third maxilliped exopod. For example, Gempala Ng & Ahmad, 2016 View in CoL , from Peninsular Malaysia has a superficially similar short, relatively stout and strongly bent G1 ultimate article with a distinct dorsal flap in addition to the absence of the flagellum on the third maxilliped exopod (see Ng & Ahmad 2016: fig. 7a, e). Capitamon n. gen. cannot be confused with Gempala View in CoL , however, because its epigastric and postorbital cristae are well-developed ( Figs 6A View FIG ; 8A View FIG ; 9A View FIG ; 12A View FIG ; 15A View FIG ; see Pati et al. 2020: figs 1a; 2a) (vs poorly developed; see Ng & Ahmad 2016: fig. 3a); the dorsal flap on G1 ultimate article is comparatively low ( Figs 6F View FIG ; 7A View FIG , C-E; 8C; 10A, B, D; 11A, C-E; 13F; 14A, C-E; 16F; 17A, C-E; see Pati et al. 2020: figs 4a-d; 5a-c) (vs conspicuously high; see Ng & Ahmad 2016: fig. 7e); and G1 penultimate article is relatively stouter ( Figs 6F View FIG ; 7D, E View FIG ; 8C View FIG ; 10A View FIG ; 11D, E View FIG ; 13F View FIG ; 14D, E View FIG ; 16F View FIG ; 17D, E View FIG ; Pati et al. 2020: figs 4a, d; 5a, c) (vs relatively slender; see Ng & Ahmad 2016: fig. 7e).

Among the Indian potamiscines, Abormon Mitra, Pati & Ng, 2021 View in CoL , and Teretamon Yeo & Ng, 2007 View in CoL , also have a G1 ultimate article with a distinct dorsal flap (see Yeo & Ng 2007: fig. 13d; Absar et al. 2017: fig. 3a; Mitra 2017: fig. 116; Mitra et al. 2018: fig. 4a; 2021: figs 3a; 7a; Mitra & Pati 2021: fig. 4a). Capitamon n. gen., however, is differentiated from Abormon View in CoL and Teretamon View in CoL mainly by the well-developed epigastric and postorbital cristae ( Figs 5A View FIG ; 8A View FIG ; 9A View FIG ; 12A View FIG ; 15A View FIG ; see Pati et al. 2020: figs 1a; 2a) (vs epigastric and postorbital cristae poorly developed; see Yeo & Ng 2007: fig. 13a; Absar et al. 2017: fig. 2a; Mitra 2017: fig. 58; Mitra et al. 2018: fig. 2a; 2021: figs 2a; 6a; Mitra & Pati 2021: fig. 2a), and the relatively shorter G1 ultimate article ( Figs 6F View FIG ; 7D, E View FIG ; 8C View FIG ; 10A View FIG ; 11D, E View FIG ; 13F View FIG ; 14D, E View FIG ; 16F View FIG ; 17D, E View FIG ; see Pati et al. 2020: figs 4a, d; 5a, c) (vs G1 ultimate article relatively longer; see Yeo & Ng 2007: fig. 13d; Absar et al. 2017: fig. 3a; Mitra 2017: fig. 116; Mitra et al. 2018: fig. 4a; 2021: figs 3a; 7a; Mitra & Pati 2021: fig. 4a). Moreover, the crabs of Capitamon n. gen. are relatively large in size (adult CW> 40 mm) than those of Abormon View in CoL (adult CW <15 mm; see Mitra et al. 2021) and Teretamon View in CoL (adult CW <27 mm; see Yeo & Ng 2007; Absar et al. 2017; Mitra 2017; Mitra et al. 2018; Mitra & Pati 2021; Pan et al. 2021).

Some Indian species of Potamiscus Alcock, 1909 [ P. chizami Pati, 2021 , P. mima Pati, 2021 , and P. takedai Pati, Mitra & Ng, 2020 ], like Capitamon n. gen., possess well-developed epigastric and postorbital cristae ( Figs 5A View FIG ; 8A View FIG ; 9A View FIG ; 12A View FIG ; 15A View FIG ; see Pati et al. 2020: figs 1a, c; 2a, f; Pati 2021: fig. 2a, g) in addition to a distinct but low dorsal flap on the G1 ultimate article ( Figs 6F View FIG ; 7A View FIG , C-E; 8C; 10A, B, D; 11A, C-E; 13F; 14A, C-E; 16F; 17A, C-E; see Pati et al. 2020: figs 4a-d, f-i; 5a-c, e-g; Pati 2021: fig. 3a, b, e, f). Capitamon n. gen., however, is immediately differentiated from Potamiscus chizami and Potamiscus mima by the low carapace ( Figs 5B View FIG ; 9C View FIG ; 12B View FIG ; 15B View FIG ; see Pati et al. 2020: fig. 2b) (vs carapace conspicuously high; see Pati 2021: fig. 2b, h) and the short ultimate article of the G1 ( Figs 6F View FIG ; 7D, E View FIG ; 8C View FIG ; 10A View FIG ; 11D, E View FIG ; 13F View FIG ; 14D, E View FIG ; 16F View FIG ; 17D, E View FIG ; see Pati et al. 2020: figs 4a, d; 5a, c) (vs G1 ultimate article elongated; see Pati 2021: fig. 3a, e). On the other hand, Capitamon n. gen. can easily be confused with Potamiscus takedai due to several characters in common, including the low carapace ( CH / CW = 0.4-0.5) ( Figs 5B View FIG ; 9C View FIG ; 12B View FIG ; 15B View FIG ; see Pati et al. 2020: fig. 2b, g), the well-developed epigastric and postorbital cristae ( Figs 5A View FIG ; 8A View FIG ; 9A View FIG ; 12A View FIG ; 15A View FIG ; see Pati et al. 2020: figs 1a; 2a, f), the deep male s2/s3 reaching lateral margins ( Figs 5C View FIG ; 6D View FIG ; 8B, E View FIG ; 12C View FIG ; 13D View FIG ; 15C View FIG ; 16D View FIG ; see Pati et al. 2020: figs 1b, d; 2e, j), the relatively broader male pleon with a broader pleonal somite 6 ( Figs 5C View FIG ; 6E View FIG ; 8B View FIG ; 9D View FIG ; 12C View FIG ; 13E View FIG ; 15C View FIG ; 16E View FIG ; see Pati et al. 2020: figs 1b, d; 2d, i), the moderately stout G1 with short, stout, strongly bent ultimate article ( Figs 6F View FIG ; 7A View FIG , C-E; 8C; 10A, B, D; 11A, C-E; 13F; 14A, C-E; 16F; 17A, C-E; see Pati et al. 2020: figs 4a-d, f-i; 5a-c, e-g), the longer G2 ( Figs 6F, G View FIG ; 7B, D View FIG ; 8C, D View FIG ; 10A, C View FIG ; 11B, D View FIG ; 13F, G View FIG ; 14B, D View FIG ; 16F, G View FIG ; 17B, D View FIG ; see Pati et al. 2020: figs 4a, e, f, j; 5a, d, e, h), and the ovate, closely located vulvae touching the s5/s6 and almost reaching the s4/s5 ( Figs 7I View FIG ; 13I View FIG ; 16I View FIG ; see Pati et al. 2020: fig. 3c, f). Capitamon n. gen. is nevertheless separated from Potamiscus takedai by the narrow to broadly triangular dorsal flap on the G1 ultimate article ( Figs 6F View FIG ; 7A View FIG , C-E; 8C; 10A, B, D; 11A, C-E; 13F; 14A, C-E; 16F; 17A, C-E; see Pati et al. 2020: figs 4a, b; 5a, b) (vs G1 ultimate article with a semicircular dorsal flap; see Pati et al. 2020: figs 4f, g; 5e, f), and the transversely broader and relatively small vulvae, occupying 0.5-0.6 times the length of the s6 ( Figs 6I View FIG ; 13I View FIG ; 16I View FIG ; see Pati et al. 2020: fig. 3c) (vs vulvae longitudinally broader and relatively large, occupying 0.8 times the length of the s6; see Pati et al. 2020: fig. 3f).

The specimens with “bird’s head-like” ultimate article of the G1, hitherto incorrectly referred to Potamon beieri , Ranguna beieri , Potamiscus beieri (Pretzmann, 1966) , or Indochinamon beieri by previous workers (see Remarks for Indochinamon beieri ) actually belong to different species of Capitamon n. gen. The NHM 1909.5.1.1 male specimen probably from Nagaland illustrated in Pretzmann (1966b: pl. 4, fig. 12; pl. 5, figs 16-18) is assigned here to a new species, C. clarki n. gen., n. sp. The specimens of I. beieri from Mizoram recorded in Mitra (2017) is recognized in the present study as C. mizoramense n. gen., n. sp. The SMF 2807 male specimen from Assam reported in Bott (1966: fig. 15; 1970: pl. 38, fig. 35; pl. 47, fig. 31) and Brandis (2000: pl. 10, fig. 2a-c) is similar to Capitamon mizoramense n. gen., n. sp. in G1 structure, but its dorsal flap on the ultimate article is comparatively low and broadly triangular (vs comparatively high and narrowly triangular; Figs 16F View FIG ; 17A View FIG , C-E). As the SMF 2807 male could not be examined in this study, we are not sure about its conspecificity with C. mizoramense n. gen., n. sp. Furthermore, Indochinamon manipurense from Manipur is also assigned to Capitamon n. gen. since it has a distinct dorsal flap on the G1 ultimate article that resembles a bird’s head ( Fig. 11A View FIG , C-E; see Pati et al. 2020: figs 4a-d; 5a-c). In addition, two more new species of Capitamon n. gen. are recognized herein, i.e., C. capitatum n. gen., n. sp. and C. meitei n. gen., n. sp.

Capitamon n. gen. currently has five nominal species: C. capitatum n. gen., n. sp. (type species); C. clarki n. gen., n. sp.; C. manipurense ( Alcock, 1909) View in CoL n. comb.; C. meitei n. gen., n. sp.; and C. mizoramense n. gen., n. sp.

KEY TO SPECIES OF CAPITAMON N. GEN.

1. G1 ultimate article completely bent at angle of about 110° from longitudinal axis of G1 ( Figs 16F View FIG ; 17D, E View FIG ; see Brandis 2000: pl. 10, fig. 2c) ....................................................................................................................... 2

— G1 ultimate article relatively less bent at angle of about 60-75° from longitudinal axis of G1 ( Figs 6F View FIG ; 7D, E View FIG ; 8C View FIG ; 10A View FIG ; 11D, E View FIG ; 13F View FIG ; 14D, E View FIG ; see Pati et al. 2020: figs 4a, d; 5a, c) .......................................................... 3

2. Cervical grooves discontinuous, not reaching to level of postorbital cristae ( Fig. 15A View FIG ); G1 ultimate article with relatively high, narrowly triangular dorsal flap ( Figs 16F View FIG ; 17A View FIG , C-E) .............................................................. ......................................................................................... C. mizoramense n. gen., n. sp. [ INDIA: Mizoram].

— Cervical grooves continuous, reaching to level of postorbital cristae (see Brandis 2000: pl. 10, fig. 2a); G1 ultimate article with relatively low, broadly triangular dorsal flap (see Brandis 2000: pl. 10, fig. 2b, c) ................. ............................................................................................................. C. aff. mizoramense [ INDIA: Assam].

3. Male pleonal somite 6 equal in length to pleonal somite 5 ( Figs 5C View FIG ; 6E View FIG ; 12C View FIG ; 13E View FIG ); G1 ultimate article with sinuous outer margin ( Figs 6F View FIG ; 7A View FIG , C-E; 13F; 14A, C-E) ............................................................................ 4

— Male pleonal somite 6 longer than pleonal somite 5 ( Figs 8B View FIG ; 9D View FIG ; see Pati et al. 2020: figs 1b; 2d); G1 ultimate article with straight outer margin ( Figs 8C View FIG ; 10A, B, D View FIG ; 11A View FIG , C-E; see Pati et al. 2020: figs 4a-d; 5a-c) ........ 5

4. Postorbital cristae straight in dorsal view ( Fig. 5A View FIG ); third maxilliped exopod lacking flagellum or with vestigial flagellum ( Fig. 6B View FIG ); male s3/s4 shallow, running from sternopleonal cavity to lateral edges of sternum ( Figs 5C View FIG ; 6D View FIG ); male pleonal somite 6 with almost straight lateral margins ( Figs 5C View FIG ; 6E View FIG ); G1 ultimate article with relatively low, broadly triangular dorsal flap ( Figs 6F View FIG ; 7A View FIG , C-E) ..................................................................................... ....................................................... C. capitatum n. gen., n. sp. [ INDIA: Arunachal Pradesh and Nagaland].

— Postorbital cristae oblique in dorsal view ( Fig. 12A View FIG ); third maxilliped exopod with short flagellum, more than half width of merus ( Fig. 13B View FIG ); male s3/s4 indiscernible ( Figs 12C View FIG ; 13D View FIG ); male pleonal somite 6 with convex lateral margins ( Figs 12C View FIG ; 13E View FIG ); G1 ultimate article with relatively high, narrowly triangular dorsal flap ( Figs 13F View FIG ; 14A View FIG , C-E) .................................................................................. C. meitei n. gen., n. sp. [ INDIA: Manipur].

5. Carapace relatively low, CH /CW = 0.4 (see Pati et al. 2020: fig. 2b); male s3/s4 indiscernible except for two short lateral clefts (see Pati et al. 2020: figs 1b; 2e); male telson relatively narrower, proximal width c. 1.2 × medial length, with strongly concave lateral margins (see Pati et al. 2020: figs 1b; 2d); G1 ultimate article relatively less strongly bent at angle of about 60° from longitudinal axis ( Fig. 11D, E View FIG ; see Pati et al. 2020: fig. 4a, d; 5a, c) ........................................... C. manipurense ( Alcock, 1909) n. comb. [ INDIA: Manipur].

— Carapace relatively high, CH /CW = 0.5 ( Fig. 9C View FIG ); male s3/s4 shallow, running from sternopleonal cavity to lateral edges of sternum ( Fig. 8B, E View FIG ); male telson relatively broader, proximal width c. 1.3 × medial length, with gently concave lateral margins ( Figs 8B View FIG ; 9D View FIG ); G1 ultimate article relatively more strongly bent at angle of about 75° from longitudinal axis ( Figs 8C View FIG ; 10A View FIG ) ................................ C. clarki n. gen., n. sp. [ INDIA: Nagaland?].