Indochinamon beieri (Pretzmann, 1966)

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 : 592-596

Indochinamon beieri (Pretzmann, 1966)

( Figs 2 ; 3 ; 4 )

Potamon beieri Pretzmann, 1966a: 5 ;b: 301, pl. 4, figs 13-15 (in part).

Potamiscus (Ranguna) rangoonensis – Bott 1966: 481, fig. 15 [not Potamon (Potamon) rangoonensis Rathbun, 1904 ].

Ranguna (Ranguna) rangoonensis – Bott 1970: 163, pl. 38, fig. 35; pl. 47, fig. 31 [not Potamon (Potamon) rangoonensis Rathbun, 1904 ].

Potamiscus andersonianus – Brandis 2000: 68 (in part) [not Telphusa andersoniana Wood-Mason, 1871 ].

Indochinamon beieri – Yeo & Ng 2007: 283 (list). — Ng et al. 2008: 163 (list). — Ng & Win Mar 2018: 49 (list). — Pati et al. 2020: 704 (list).

TYPE MATERIAL. — Holotype. Myanmar • ♂ (29.3 × 23.6 mm); Kayin state: Myawaddy district: “Sukli” [Su Ka Li], eastern side of Dawna Hills, near Myanmar-Thailand border ; [c. 16°9’18”N, 98°35’52”E]; alt. 366 m; no date; F. H. Gravely leg.; NHM 1934.1.15.1 (“Exch: Indian Museum” “9770/10”).

OTHER MATERIAL. — Myanmar • ♀ (31.3 × 25.2 mm); same data as for holotype; NHM 1934.1.15.2 (“Exch: Indian Museum” “9770/10”) .

DIAGNOSIS. — Carapace ovate, broader than long (CW/CL = 1.3), relatively low ( CH /CW = 0.4); dorsal surface gently convex in frontal view; 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, outer margin short; epibranchial tooth low, blunt; cervical grooves shallow, narrow, discontinuous, not reaching to level of postorbital cristae; epibranchial region with closely spaced granules; suborbital margin joining with supraorbital margin; epistome posterior margin with well-developed, triangular median tooth ( Fig. 2 A-C). Third maxilliped exopod with short flagellum, shorter than width of merus ( Fig. 3A ). Chelipeds rugose, subequal, carpus with prominent, narrow, triangular inner distal major tooth and low subbasal tooth ( Figs 2A ; 3C ). Ambulatory legs short, stout, with short setae on margins ( Fig. 2A ). Male s2/s3 deep, reaching lateral margins; male s3/s4 indiscernible ( Figs 2D ; 3D ). Male sternopleonal cavity long, reaching to imaginary line joining medial part of cheliped coxae ( Figs 2D ; 3D ). Male pleon relatively narrow; pleonal somite 6 trapezoidal, broader than long (proximal width c. 1.8 × medial length), longer than pleonal somite 5, with almost straight lateral margins ( Figs 2D ; 3B ). Male telson triangular, slightly longer than pleonal somite 6, relatively narrow (proximal width c. 1.2 × medial length), with gently concave lateral margins ( Figs 2D ; 3B ). G1 slender, with ultimate article gently curved outwards at angle of about 25° from longitudinal axis, tip blunt, reaching pleonal locking structure; ultimate article relatively slender, short, c. 0.3 × combined length of flexible zone and penultimate article, subcylindrical, distally abruptly narrow, lacking dorsal flap, penultimate article relatively slender, gently sinuous ( Figs 3D, E ; 4 A-C). G2 long, c. 1.2 × length of G1; ultimate article long, c. 0.6 × length of penultimate article ( Figs 3F ; 4D ). Female pleon together with telson broadly ovate ( Fig. 3G ). Vulvae on s6 positioned close to each other, ovate, opening mesially, relatively small, occupying 0.6 × length of s6, touching s5/s6, some distance from s4/s5, laterally partially covered by protruding sternal cover, visible in ventral view ( Fig. 3H ).

GEOGRAPHICAL DISTRIBUTION. — Indochinamon beieri is known only from the type locality, i.e., Su Ka Li, eastern side of Dawna Hills, Myawaddy district, Kayin state, Myanmar ( Fig. 1 ).

REMARKS

Pretzmann (1966a: 5, 6), during his visit to the NHM between 1963 and 1964, briefly diagnosed a new species, Potamon beieri , from a single male specimen(23.5 mm CL) from “Sukli,Dawane Hills, 1200 ft., 1934 coll.”, characterizing it by a G1 that was described as follows: “Gonopoden schlank, Subterminalglied am Ende fast rechtwinkelig nach aussen abgewinkelt. Terminalglied setzt diese Richtung fort. Innenkante stark ausgebuchtet, so dass der Umriss des Gonopoden an einen Vogelkopf erinnert. Innenkante des Subterminalgliedes dicht behaart bis zur Hälfte, Aussenkante mit einer Reihe langer Borsten.” [Gonopods slender, subterminal segment angled outwards almost at right angles at tip.Terminal member continues this direction. Inner edge strongly bulged, so that the outline of the gonopod resembles a bird’s head. Inner edge of subterminal segment densely haired up to halfway, outer edge with a row of long bristles.] (translation ours). No figures or catalogue number was provided in the original publication. Pretzmann (1966b: 301, pl. 4, figs 12-15) subsequently described the species in greater detail with figures of the specimen and its supposed G1. The G1 figured ( Pretzmann 1966b: pl. 4, fig. 12) matches his original description ( Pretzmann 1966a: 5, 6). No catalogue number was provided by Pretzmann (1966b), but the figures he provided of the dorsal, frontal and ventral views of the specimen (see Pretzmann 1966b: pl. 4, figs 13-15) perfectly match a male specimen in a jar with the catalogue number NHM 1934.1.15.1-2, which also contains a female (31.3 × 25.2 mm) collected at the same time. There are no labels inside the bottle indicating the specimen(s) was examined by Pretzmann or that the male is a type. This male specimen, measuring 29.3 × 23.6 mm agrees well in the measurements, and has a distinctive small round scar on the right side of the cardiac region ( Fig. 2A, C ; also see Pretzmann 1966b: pl. 4, fig. 15). As such, we have no doubt this is the specimen Pretzmann (1966a, b) designated and figured as the holotype male specimen of Potamon beieri . We here select the catalogue number NHM 1934.1.15.1 for the holotype male of Potamon beieri , with the number NHM 1934.1.15.2 assigned to the female. The female specimen is a not a type as it was not mentioned by Pretzmann (1966a, b). The type locality of the specimen should be “Sukli” [Su Ka Li], eastern side of Dawna Hills (not Dawane Hills), and in the original label, it states that this site is near the Myanmar-Thailand border.

Pretzmann (1966b: 303, pl. 5, figs 16-18) also figured a specimen of “ Potamon andersonianum andersonianum ” (dorsal, frontal and ventral views only, no G1) in his paper treating specimens from NHM, but no data was provided. The species, however, was not even mentioned by Pretzmann (1966b) in the main text. We are certain this specimen is the one now catalogued in the NHM as “ Potamon andersonianum andersonianum ” under the catalogue number NHM 1909.5.1.1. Alcock (1910: 35) had originally identified this specimen as “ Potamon (Potamon) andersonianum var. rangoonense ”, who listed four males and two females under the “Indian Museum” [ZSIK] catalogue number 4115/4 from an unknown locality collected by “Captain Butler”. One of these male specimens was gifted to NHM and was catalogued as “1909.5.1.1”. The labels with the NHM specimen indicate it was determined by “A. Alcock”, “ex 4115/4” and presented by the Indian Museum, and the locality was stated as “ Burma ” [present day Myanmar].The same specimen (NHM 1909.5.1.1) was later examined and listed as “ Potamon beieri ” byBrandis (2000: 75) as being collected from Myanmar. Specimen NHM 1909.5.1.1, however, is unlikely to have been collected from Myanmar.The collector, “Captain Butler”, was almost certainly the Permanent Official assigned by the Lieutenant-Governor of Bengal in 1869 to manage Nagaland in northeastern India (see Johnstone 1896; Bhatia 2004), and likely the specimen was obtained from Nagaland instead. The specimen Pretzmann (1966b: pl. 5, figs 16-18) figured matches NHM 1909.5. 1.1 in all respects.

The problem with the identity of Potamon beieri is that the G1 figured by Pretzmann (1966b: pl. 4, fig. 12) does not belong to the holotype. The actual G1 of the holotype of Potamon beieri (NHM 1934.1.15.1) is more slender and much straighter, with the ultimate article cylindrical and gently curved outwards (not bent at almost right angle to the penultimate article) ( Figs 3E ; 4 A-C). The G1 he figured ( Pretzmann 1966b: pl. 4, fig. 12), actually belongs to NHM 1909.5.1.1 ( Fig. 8C ). Although the left G1s of both specimens had been detached and placed in separate vials in their respective jars (leading to the possibility they had been accidentally misplaced), it is fortunate that the right G1s are still attached to the specimens ( Figs 3D ; 8E ) and confirm our interpretation. Pretzmann (1966a, b), therefore, had confused the G1s of the two specimens. This observation is also aligned with the discussion earlier that specimen NHM 1909.5.1.1 was likely to have been collected from Nagaland or its environs rather than Myanmar; all the species we have seen with this distinctive form of G1 have been from that area.

The incorrect G1 figured by Pretzmann (1966b) for Potamon beieri has caused substantial confusion in the identity of this species. Brandis (2000) discussed the taxonomy of this species, identified three specimens each from Assam (SMF 2807), Naga Hills (NMB 951a) and Myanmar (NHM 1909.5.1.1). Brandis (2000) followedPretzmann (1966a, b) in characterizing the species as one with a sharply bent G1 ultimate article and provided figures for the SMF 2807 male specimen, including its G1 (see Brandis 2000: pl. 10, fig. 2a-c). Brandis (2000: 78) observes: “Especially characteristic for P. beieri is the terminal joint of the G1. Here a true torsion of the terminal joint turns the whole joint at 180° in relation to the subterminal joint. Due to this torsion the original dorsal side appears ventrally. This special character does not occur in any other potamid crab as far as known. It must have a special function in copulation process that only could be studied with live specimens.” Brandis (2000) noted that Bott (1966: 481, fig. 15; 1970: 163, pl. 38, fig. 35; pl. 47, fig. 31) –who also provided figures for the SMF 2807 male specimen– had misidentified the species as “ Ranguna rangoonense (Rathbun, 1904) ”. Türkay & Naiyanetr (1987), while citing Pretzmann (1966b: pl.4, fig.12), observed that the G1 of the SMF 2807 male specimen is very similar to that of Potamon beieri , with only difference in the angle between the ultimate and penultimate articles. Türkay& Naiyanetr (1987) argued that the said difference could be due to size differences and treated the SMF 2807 specimen as Ranguna beieri (Pretzmann, 1966) , or possibly as Potamon (Potamon) pruinosum Alcock, 1909 . Potamon (Potamon) pruinosum is entirely different from Potamon beieri or SMF 2807 specimen in G1 structure, and the species has already been assigned to Stelomon Yeo & Naiyanetr, 2000 (see Yeo & Naiyanetr 2000: 1630, fig. 3c). Neither Türkay & Naiyanetr (1987) nor Brandis (2000) correctly identified Potamon beieri as they were referring to the G1 described or illustrated in Pretzmann (1966a, b), which belonged to the NHM1909.5.1.1 specimen and was not that of the holotype (NHM 1934.1.15.1). In fact, Brandis (2000: 68, 71) incorrectly included the NHM 1934.1.15.1- 2 specimens from “Sukli” under “ Potamiscus andersonianus (Wood-Mason, 1871) ”. Recently, Mitra (2017) identified several specimens from Mizoram state of northeastern India as I. beieri . Those specimens from Mizoram also differ in G1 morphology from that of the holotype of Potamon beieri .

All the confusion regarding the identity of Potamon beieri was probably because the NHM 1934.1.15.1 specimen was not properly labelled as a type in the first place. The incorrect G1 figure in Pretzmann (1966b: pl. 4, fig. 12) is another major reason for the previous misunderstanding of what the species is. The actual identities of these misidentified specimens are now revealed.The NMB 951a male specimen from Naga Hills has already been refereed to Ranguna rangoonensis (Rathbun, 1904) byNg & Yeo (2023). The NHM 1909.5.1.1 male probably from Nagaland, the SMF 2807 male from Assam and the specimens examined by Mitra (2017) from Mizoram are all assigned herein to a new genus, Capitamon n. gen. (see Remarks for Capitamon n. gen.).

In the G1 structure, I. beieri s. str. most closely resembles I.andersonianum (Wood-Mason, 1871) [Yunnan, southwestern China], I. chinghungense (Dai, Song, He, Cao, Xu & Zhong, 1975) [Yunnan, southwestern China], I. gengmaense (Dai, 1995) [Yunnan, southwestern China], I. khinpyae Ng & Win Mar, 2018 [northern Myanmar], I. kimboiense (Dang, 1975) [northern Vietnam], I. orleansi (Rathbun, 1904) [northern Vietnam], I. phongnha Naruse, Nguyen & Yeo, 2011 [central Vietnam], and I. prolatum ( Brandis, 2000) [northern Thailand] due to the relatively shorter and slenderer ultimate article ( Figs 3E ; 4 A-C; see Yeo & Ng 1998: fig. 2i; Dai 1999: figs 86 (4); 98 (4); Brandis 2000: pl. 13, fig. 2c; Naruse et al. 2011: figs 3b; 9b; Ng & Win Mar 2018: fig. 4b; unpublished data on I. andersonianum ). Indochinamon beieri is nevertheless distinguished from all the above species mainly by the gently curved ultimate article, i.e., curved outwards at an angle of about 25° from longitudinal axis of the G1 ( Figs 3E ; 4A ) (vs G1 ultimate article relatively strongly bent at an angle of about 45-60° from longitudinal axis; see Yeo & Ng 1998: fig. 2i; Dai 1999: figs 86 (4); 98 (4); Brandis 2000: pl. 13, fig. 2c; Naruse et al. 2011: figs 3b; 9b; Ng & Win Mar 2018: fig. 4b; unpublished data on I. andersonianum ). In addition, I. beieri can be also distinguished from all of them, except for I. khinpyae , by the abruptly narrow tip of the G1 ultimate article ( Figs 3E ; 4 A-C; see Ng & Win Mar 2018: fig. 4b) (vs G1 ultimate article with a gradually narrow tip; seeYeo & Ng 1998: fig. 2i; Dai 1999: figs 86 (4); 98 (4); Brandis 2000: pl. 13, fig. 2c; Naruse et al. 2011: figs 3b; 9b; unpublished data on I. andersonianum ). Indochinamon beieri can still be differentiated from I. khinpyae by the relatively slender penultimate article of the G1 ( Figs 3E ; 4 A-C) (vs G1 penultimate article relatively stouter; see Ng & Win Mar 2018: fig. 4b).

Figures

FIG. 2. — Indochinamon beieri (Pretzmann, 1966), holotype ♂ (29.3 × 23.6 mm) (NHM 1934.1.15.1): A, overall dorsal view; B, frontal view of cephalothorax; C, dorsal view of cephalothorax; D, s1-s7, pleonal somites 4-6, and telson. Not to scale.

FIG. 3. — Indochinamon beieri (Pretzmann, 1966), holotype ♂ (29.3 × 23.6 mm) (NHM 1934.1.15.1) (A-F), ♀ (31.3 × 25.2 mm) (NHM 1934.1.15.2) (G, H): A, right third maxilliped; B, pleon and telson; C, chela (outer view); D, s1-s8 showing right G1 in situ; E, left G1 (ventral view); F, left G2; G, pleonal somites 4-6 and telson; H, s1-s8 showing vulvae. Not to scale.

FIG. 4. — Indochinamon beieri (Pretzmann, 1966), holotype ♂ (29.3 × 23.6 mm) (NHM 1934.1.15.1): A, left G1 (ventral view); B, left G1 ultimate article (dorsal view); C, left G1 ultimate article (ventral view); D, left G2. Scale bar: A, D, 1 mm; B, C, 0.5 mm.

FIG. 1. — Map showing Myanmar, India, northeastern India, and distribution of Indochinamon beieri (Pretzmann, 1966) and the species of Capitamon n. gen.

FIG. 8. — Capitamon clarki n. gen., n. sp., holotype ♂ (42.1 × 32.9 mm) (NHM 1909.5.1.1): A, overall dorsal view; B, s1-s7, pleonal somites 4-6, and telson; C, left G1 (ventral view); D, left G2; E, s1-s8 showing right G1 in situ. Not to scale.