Arcotheres vicajii ( Chhapgar, 1957 ) Trivedi & Gosavi & Vachhrajani & Mitra & Ravinesh & Ng, 2020

Trivedi, Jigneshkumar N., Gosavi, Swapnil, Vachhrajani, Kauresh D., Mitra, Santanu, Ravinesh, Raveendhiran & Ng, Peter K. L., 2020, On the identities of Nepinnotheres vicajii (Chhapgar, 1957) and Arcotheres casta (Antony & Kuttyamma, 1971) from western India: conspecificity and taxonomy (Decapoda, Brachyura, Pinnotheridae), Zootaxa 4809 (3), pp. 496-508 : 497-507

publication ID	https://doi.org/ 10.11646/zootaxa.4809.3.4
publication LSID	lsid:zoobank.org:pub:55DB6154-6C9F-41C7-8327-F0CF2EC0DA65
persistent identifier	https://treatment.plazi.org/id/C25887AE-FFA4-FFF5-55FC-FD3DFC15FDB9
treatment provided by	Plazi
scientific name	Arcotheres vicajii ( Chhapgar, 1957 )
status	comb. nov.

Treatment

Arcotheres vicajii ( Chhapgar, 1957) View in CoL comb. nov

( Figs. 1–8 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 View FIGURE 5 View FIGURE 6 View FIGURE 7 View FIGURE 8 )

Pinnotheres vicajii Chhapgar, 1957: 505 View in CoL , 506, pl. 12, fig. n, o–q; Chhapgar 1958: 253–256, fig. 2; Silas & Alagarswami 1967:

1212; Schmitt et al. 1973: 90 (discussion); Kumari & Rao 1974:165–172, figs. 1–19; Ng et al. 2008: 251 (list); Pati et al.

2012: 384 (list). Nepinnotheres vicajii — Ng & Kumar 2015: 265 (discussion); Trivedi et al. 2018b: 62 (list). Pinnotheres casta Antony & Kuttyamma, 1971: 59–68 , figs.1, 2; Schmitt et al. 1973: 94 (discussion) Pinnotheres sp.— Silas & Algarswami 1967: 1163–1173, pls. 1–3, text fig. 1, 2. Schmitt et al. 1973: 94 (discussion) Arcotheres casta — Ng & Kumar 2015: 265 (discussion); Ng et al. 2017: 1094 (discussion); Trivedi et al. (2018a): 197 (Discus-

sion); Trivedi et al. (2018b): 61 (list).

Material examined. Holotype: male (CW 3.7 mm, CL 3.7 mm) ( ZSI-C 3361/1) Mumbai in Marcia recens (Holten, 1802) , Maharashtra state, India, coll. B. F. Chhapgar, 17 April 1953; Others: 2 females (CW 8.6 mm, CL 7.7 mm; CW 8.9 mm, CL 7.8 mm) ( LFSC.ZRC-115) Mumbai in Meretrix aurora Hornell, 1917 , Maharashtra state, India, coll. S. Gosavi, 27 Sepetmber, 2018; 3 males (CW 4.3 mm, CL 4.1 mm; CW 4.5 mm, CL 4.2 mm; CW 4.7 mm, CL 4.4 mm), 1 non-ovigerous female (CW 8.0 mm, CL 6.7 mm), 1 ovigerous female (CW 8.2 mm, CL 6.9 mm) ( ZRC 2018.0768), in Marcia recens (Holten, 1802) , Tamil Nadu, India, coll. R. Ravinesh, 2016; 1 juvenile female (CW 4.0 mm, CL 3.6 mm) ( ZRC 2018.0769), in Marcia recens (Holten, 1802) , Tamil Nadu, India, coll. R. Ravinesh, 2016.

Description. Female: carapace subhexagonal ( Figs. 1A View FIGURE 1 , 2A View FIGURE 2 , 8A View FIGURE 8 , 5A, 5D View FIGURE 5 ), wider than long, regions poorly defined, anterior margin well defined; front slightly projecting, transverse; posterior margin almost straight. Eyes small, partially visible in dorsal view; orbits ovate ( Figs. 1A View FIGURE 1 , 8A View FIGURE 8 , 5B, 5C View FIGURE 5 ). Antennules folded obliquely ( Fig. 2E View FIGURE 2 ), antennular fossa slightly larger than ocular cavities. Antennae with 6 articles ( Fig. 2E View FIGURE 2 ); basal article with rectangular tubercle, fused with epistome, distal segment setose, scarcely overreaching orbito-antennular fossae. Margin of first thoracic sternite emarginated. MXP3 ( Figs. 2F View FIGURE 2 , 6A, L View FIGURE 6 ) obliquely placed in buccal cavity, outer surface with scattered setae on mesial margin, inner margin with fringe of long setae; propodus about 2.4 times as long as high, stout, longer than carpus, dorsal margin with fringe of long setae, anterior margin rounded with long setae; digitiform dactylus distally setose, inserted medially in notch on ventral margin of propodus, distally almost reaching tip of propodus (sometimes shorter); overreaching anteromesial angle of merus; ischium and merus fused, indistinguishable, about 2.1 times as long as wide, lateral margin gently convex, mesial margin usually angular at widest point forming anteromesial angle, inner margin gently concave with fringe of long slender setae. Exopod ( Figs. 2F View FIGURE 2 , 6A View FIGURE 6 ) longer than half length of ischiomerus, flagellum with 2 articles, distally with fine setae.

P1 (Cheliped) ( Figs. 1A View FIGURE 1 , 8A View FIGURE 8 , 5A, 5B View FIGURE 5 ) stout, merus slightly longer than carpus; chela ( Figs. 2C, D View FIGURE 2 , 6B View FIGURE 6 ) slightly globose, ventral margin gently convex, outer margin slightly curved, palm about 2.0–2.5 times as long as high; dactylus and pollex shorter than dorsal margin of palm, longer than greatest width of palm, palm relatively stout; dactylus cutting edge fringed with short setae, 1 large tooth present proximally, ending with sharp claw, dactylus inner surface with scattered setae. Pollex cutting edge with fringe of short setae, 3 teeth proximally, median tooth smaller, pollex inner surface with patch of long setae.

P2, P3, P5 subequal from left to right ( Figs. 4A, B View FIGURE 4 , D–F, H, 6C, D, F, G, I); P2, P3 ( Figs. 4A, B, E, F View FIGURE 4 , 6C, D, G, J, K View FIGURE 6 ) similar in shape; merus, carpus, propodus glabrous, propodus longer than carpus, slightly curved on both margins; dactylus conical, shorter than carpus and propodus, ventral margin with short fine setae distally. P4 ( Figs. 4C, G View FIGURE 4 , 6E, H View FIGURE 6 ) markedly asymmetrical with left or right side distinctly longer, more elongate than P2, P3, P5; articles (except dactylus) similar in shape to those of P2, P3; longer P4 more slender than P2, P3; dactylus sickle-like, shorter than propodus, ending in small curved tip, longer than dactyli of P2, P3, ventral margin with short setae present distally. P5 ( Figs. 4D, H View FIGURE 4 , 6F, I View FIGURE 6 ) more slender than P2–P4; articles (except dactylus) similar in shape to P2–P4; dactylus longer, tapering distally, much longer than in P2–P4; ventral margin of P5 dactylus with long fine setae, tip (fig. 4I) with row of short spines, ending in sharp curved spine. Relative length of ambulatory legs P4>P5>P3>P2 and dactyli, P5>P4>P3>P2.

Pleon ( Fig. 2D View FIGURE 2 , 8B View FIGURE 8 ) wide with 6 free somites and telson, covering bases of ambulatory legs; fourth somite constricted in the middle; somites widening from 1–5, decreasing towards telson.

Male: carapace subovate ( Figs. 1B View FIGURE 1 , 3A View FIGURE 3 , 8B View FIGURE 8 , 5E View FIGURE 5 ), regions not clearly defined, front projecting anteriorly, emarginated, with flat anterior margin, eyes visible in dorsal view, MXP3 as in female. Cheliped ( Figs. 3C View FIGURE 3 , 5E View FIGURE 5 , 7B View FIGURE 7 , 8B View FIGURE 8 ) stouter, shorter than female, dorsal and ventral margin slightly undulated, ventral margin with fringe of long setae, outer margin curved; dactylus shorter than dorsal margin of palm, cutting edge with 2 large teeth, covered with short scattered setae, ending in sharp claw; pollex ventral margin with fringe of long setae, cutting edge with 1 large tooth proximally, ending in sharp claw, covered with scattered short setae.

P2–P5 ( Figs. 4 View FIGURE 4 J–M, 5E, 7C–F, 8B) more slender than cheliped; dorsal margin of merus and carpus naked, P2 merus ventral margin glabrous, P3 merus ventral margin with patch of short setae present distally, P4, P5 merus ventral margin covered with long setae; P2 carpus ventral margin naked, P3 carpus ventral margin covered with long setae, outer surface with patch of long setae distally, P4, P5 carpus ventral margin covered with long setae; P2 propodus ventral margin with short scattered setae, dorsal margin glabrous, P3 propodus ventral margin with patch of long setae distally, outer surface with fringe of long setae running parallel to dorsal margin, P4 propodus ventral margin covered with long setae, patch of long setae present dorso-distally, P5 propodus ventral margin covered with long setae, patch of short setae present dorso-distally; dactylus sickle- like, ending in sharp claw, P2 dactylus ventral margin with short setae, dorsal margin naked, P3–P5 dactylus dorsal and ventral margin covered with long setae. Relative length of ambulatory legs P4>P3>P2>P5 and dactyli of ambulatory legs P4>P5>P3>P2.

Pleon ( Figs. 3B View FIGURE 3 , 7G View FIGURE 7 ) broadly triangular, with 6 free somites and telson, widest at somite 3, decreasing towards semicircular to broadly triangular telson. G1 ( Figs. 3D View FIGURE 3 , 7H, I View FIGURE 7 ) long, curved, with acute curved tip, shallow furrow running parallel to dorsal margin, dorsal and ventral surface with long setae; G2 ( Figs. 3E View FIGURE 3 , 7J View FIGURE 7 ) stout with blunt tip, exopod elongated.

Distribution: The species is so far only reported from Maharashtra state ( Chhapgar 1957, 1958; Schmitt et al. 1973; Pati et al. 2012), Goa state ( Kumari & Rao 1974) as well as Kerala ( Antony & Kuttyamma 1971) and Tamil Nadu (present data).

Remarks. Chhapgar (1957) named Pinnotheres vicajii on the basis of six specimens (two males, four females) collected from what was then identified as “ Paphia malabarica (Dilwyn, 1817) ” (Mollusca: Venerida: Veneridae ) from Mumbai, Maharashtra state, India. Chhapgar (1957: 505), however, cited his paper that was supposed to have described this species as “ Pinnotheres vicajii, Chhapgar, Rec. lnd. Mus. liii (in press) (1955).” This 1955 paper was not published at the time of Chhapgar’s (1957) work and was actually only released three years later ( Chhapgar 1958). Chhapgar (1957) stated that the type is a “Male, No. C3361/1, Zoological Survey of India (Ind. Mus.), Calcutta.”, and we have located this specimen as part of the study. The location of the remaining male and four female specimens (all paratypes), however, is not known and are believed to be lost. The holotype male specimen agrees with other material on hand of this species as well as the account by Kumari & Rao (1974). As such, we are confident all the material is conspecific.

The description of Pinnotheres vicajii is relatively brief, and in the proportions of the legs, the way Chhapgar

(1957: 505) describes them suggests that the left and right legs are symmetrical. The figure of the species is of a male ( Chhapgar 1957: pl. 12 fig. 12n, o) and a female ( Chhapgar, 1957: pl. 12 fig. 12p, q); but the drawings of the overall specimens are rather schematic and only the left or right legs are drawn, so it is not possible to ascertain if they are symmetrical. In any case, the figure of the female specimen in Chhapgar (1957: pl. 12 fig. p, q) is imprecise and does not match with his description. His figure ( Chhapgar 1957: pl. 12 fig. p) shows the dactylus of the longer P4 and P5 as equal in length but measurements of these structures show that the dactylus of P5 is a actually longer than that of P4. Ng & Kumar (2015: 265) commented that judging from the original descriptions and figures (notably the structures of the MXP3 and P2–P5) that Pinnotheres vicajii should be moved to Nepinnotheres Manning, 1993 .

In the present study, we examined fresh female specimens referable to Pinnotheres vicajii collected from the type locality as well as the male holotype of the species. The following characters are clear: subhexagonal carapace, a dactylus of the MXP3 that is digitiform and may extend to the tip of the propodus, a P4 that is asymmetrical (right side longer), and the P4 and P5 dactyli are longer and different in structure compared to those of P2 and P3. These are the generic characters of Arcotheres Manning, 1993 ( Bürger 1895; Campos 2001; Campos & Manning 2001; Trivedi et al. 2018c). As such, we transfer Pinnotheres vicajii Chhapgar, 1957 , to Arcotheres .

In the present study, the fresh material of A. vicajii comb. nov. from Mumbai has been collected from Meretrix aurora Hornell, 1917 , but the type material recorded by Chhapgar (1958) was from Marcia recens (Holten, 1802) (recorded as Paphia malabarica (Dilwyn, 1817)) . The identity of the host species has been debated, with “ Paphia malabarica (Dilwyn, 1817) ” actually a junior synonym of Protapes gallus (Gmelin, 1791) , with the correct name being Marcia recens (Holten, 1802) (see Arathi et al. 2018). Sukumaran et al. (2019) argued that Paphia malabarica is a good species, but the taxonomy and nomenclature does not support this and as such, we follow Arathi et al. (2018) in using the name Marcia recens for the host.

Silas & Alagarswami (1967) described and figured in detail an unidentified species of pinnotherid obtained from the venerid clam Meretrix casta (Gmelin, 1791) (Mollusca: Venerida: Veneridae ) from Cochin in southwestern India. Antony & Kutyamma (1971) subsequently collected the same species from the same host from Kayamkulum Lake in Alappuzha and Kollam district of Kerala state and described it as a new species, Pinnotheres casta . On the basis of the characters, this is clearly a species of Arcotheres . The present specimens from southern India (ZRC 2018.0768, ZRC 2018.0769) agree very well with the accounts by Silas & Alagarswami (1967) and Antony & Kutyamma (1971) of the species. The figure of the overall female habitus by Antony & Kutyamma (1971: fig. 1A) is rather schematic but those of the MXP3 and ambulatory legs clearly show the asymmetry and leg proportions (Antony & Kutyamma, 1971: figs.1B, 2) (see also Silas & Alagarswami, 1967: text-fig. 2). Silas & Alagarswami (1967) had males of the species and their figures of the G1 and MXP3 (Silas & Alagarswami, 1967: text-fig. 1(4–6)) also match those we have on hand and we have no doubt they are conspecific. We have tried to find the type specimens since 2016 but we now confident they are no longer extant (A. Antony, pers. comm.).

Comparisons of our material of A. vicajii comb. nov. and A. casta show that both should be regarded as the same species. The following key structures are shared: male and female carapace shapes ( Figs. 1A, B View FIGURE 1 , 2A View FIGURE 2 , 3A View FIGURE 3 , 5A, D, E View FIGURE 5 , 8A, B View FIGURE 8 ); male chela (including dentition of the fingers) ( Figs. 3C View FIGURE 3 , 7B View FIGURE 7 , 8B View FIGURE 8 ); male P2–P5 ( Figs. 4 View FIGURE 4 J–M, 5E, 7C–F, 8B); female P2–P5 ( Figs. 4 View FIGURE 4 A–I, 6C–I), except that the right P4 is longer in A. vicajii comb. nov. ( Fig. 4G View FIGURE 4 ) instead of the left in A. casta ( Fig. 6E View FIGURE 6 ); and G1 (including the structure of the apical lobe) ( Figs. 3D View FIGURE 3 , 7H, I View FIGURE 7 ); and G2 ( Figs. 3E View FIGURE 3 , 7J View FIGURE 7 ). The female chelipeds in A. vicajii comb. nov. are slightly stouter than in A. casta (Fi g. 2B, C versus Fig. 6B View FIGURE 6 ) but this is not significant. The shapes of the male pleon are similar expect that in A. vicajii comb. nov., the telson is more semicircular, and the lateral margins of somites 3 and 6 are convex ( Fig. 3B View FIGURE 3 ) (telson more broadly triangular and lateral margins of somites 3 and 6 straighter to more sinuous in A. casta ( Fig. 7G View FIGURE 7 ). This is probably not significant as the males of A.casta examined are somewhat larger than those of A. vicajii comb. nov.

There are some differences in the form of the MXP3 but we are of the opinion they can be explained by individual variation. Kumari & Rao’s (1974) specimens of A. vicajii comb. nov. from Mandovi estuary in Goa state has a female MXP3 that has the digitiform dactylus almost reaching the anteromesial angle ( Kumari & Rao 1974: fig. 3) while it is overreaching in the present specimens ( Fig. 2F View FIGURE 2 ); the ischiomerus being wider at the anteromesial angle ( Kumari & Rao 1974: fig. 3). This may be an artefact of how the structure was drawn, with the MXP3 possibly not figured in a horizontal plane. The tip of the dactylus almost reaches the tip of the propodus in A. vicajii comb. nov. ( Fig. 2F View FIGURE 2 ) but in A. casta , the dactylus is slightly shorter ( Figs. 6L View FIGURE 6 , 7A View FIGURE 7 ). In one female of A. casta examined, the dactylus is particularly short, being only about half the length of the propodus ( Fig. 6A View FIGURE 6 ) but this may have been due to prior damage. Although the length of the dactylus relative to the propodus is a useful character in pinnotherid systematics, there is clearly more variation in this character than is generally appreciated and should be used after consideration of good sample size (e.g., see Trichobezoares villosissimus (Doflein, 1904)) ( Ng 2018) . The mesial margin of the ischiomerus is usually sharply angular ( Figs. 2F View FIGURE 2 , 6A View FIGURE 6 , 7A View FIGURE 7 ) but in one specimen, the margin is rounded ( Fig. 6L View FIGURE 6 ); this again is probably due to individual variation.

In the subhexagonal carapace, slightly projecting front, dentition of the chela and general proportions of the legs, A. vicajii comb. nov. most closely resembles A. exiguus ( Bürger 1895) (known only from one poorly preserved female from the Philippines) and A. winckworthi ( Gordon, 1936) (known only from females from Penang, Peninsular Malaysia). The host for A. exiguus is not known while A. winckworthi is also from venerid clams.The three species, however, appear to differ in the shape of the posterior carapace margin, visibility, MXP3 structures and relative lengths of the ambulatory dactyli ( Table 1). The differences are not substantial, and these species are probably conspecific. The last author is currently revising the species of Arcotheres living in venerid clams in Southeast Asia and indications are that most of these characters may be subject to variation when a large series of specimens is examined. Arcotheres vicajii comb. nov. (and A. casta ), however, are both found in venerid clams in the western part of the Indian Ocean whereas A. exiguus and A. winckworthi occur some distance away in Southeast Asia, so they are treated as separate species untill the ongoing study is completed.