Arcotheres shahi, Trivedi & Campos & Vachhrajani, 2018

Trivedi, Jigneshkumar N., Campos, Ernesto & Vachhrajani, Kauresh D., 2018, A new pea crab species of the genus Arcotheres Manning, 1993 (Crustacea: Decapoda: Brachyura: Pinnotheridae) from India, Zootaxa 4433 (1), pp. 195-200 : 196-199

Arcotheres shahi n. sp.

( Figs. 1–3 )

Material examined. Holotype, female (CL 6.13 mm, CW 6.77 mm) (ZL-AR-CR-97), in Crassostrea madrasensis (Preston, 1916) , from Pamban Fishing Harbor, Tamil Nadu, India, 9°16'56"N, 79°12'31"E, 2 February 2016, coll. J. Trivedi & D . Patel. Paratypes: 1 female (CL 3.43 mm, CW 3.30 mm), 1 male (CL 3.50mm, CW 4.14mm), ZL-AR- CR-98, same data as holotype .

Description. Female: carapace sub-trapezoidal ( Fig. 1A ), slightly wider than long, regions moderately defined, anterolateral margin cristate, front slightly projecting, relatively convex, posterior margin slightly concave. Eyes small, pigmented, not visible in dorsal view; orbits oval. Antennules folded obliquely, antennular cavities slightly larger than ocular cavities ( Fig. 1B ); antennae 6-segmented, basal segment with large, quadrate urinal article ( Fig. 1B ), fused with epistome, distal segment setose, scarcely reaching beyond inner edge of orbit. Epistome, endostome separated, margin of first thoracic sternite emarginated. MXP3 obliquely placed in buccal cavity, propodus rhomboidal about twice as long as high, longer than carpus, dorsal margin with fringe of short setae, digitiform dactylus distally setose, inserted medially in notch on ventral margin of propodus, distally not overreaching tip of propodus but overreaching anteromesial angle of merus; ischiomerus completely fused ( Fig.1F ), 1.80 times as long as wide, lateral margin convex, with short, scattered setae; mesial margin angular at the widest point forming anteromesial angle, with long, slender setae. Exopod slightly longer than half length of ischiomerus, flagellum with three articles before aesthetascs, small distal segment inconspicuously articulated ( Fig. 1F ).

Chelipeds (P1) stouter than ambulatory legs (P2–5), merus slightly longer than carpus ( Fig. 1A ); chela slightly globose ( Figs. 1D, E ), ventral margin gently convex, dactylus shorter than dorsal margin of palm, longer than greatest height of palm, small scattered patches of granules present on outer surface, distal tip pointed, strongly curved ( Fig.1D ), cutting edge with one large proximal tooth, few small teeth distally, with long setae on inner surface. Pollex with two large, proximal teeth separated by denticulate notch, patch of short setae present just below cutting edge visible on outer surface, row of long setae running parallel to cutting edge visible on inner surface ( Fig. 1E ), outer surface of palm slightly convex, inner surface highly convex.

Ambulatory legs (P2–5) asymmetrical in length ( Figs. 3A–D ), those on left side longer than corresponding legs on right side ( Fig. 1A , Figs. 3A–D ; A’–C’); P2, P3 ( Figs. 3A–B ; A’–B’) similar, with merus, carpus, propodus, dactylus glabrous; propodus longer than carpus, slightly curved on both margins; dactylus conical, shorter than carpus, propodus, hooked at tip. Fourth pereopods markedly asymmetrical ( Figs. 3C , C’), longer P4 ( Fig. 3C ) slender than P2, P3; carpus outer margin curved; dactylus sickle-like, ending in small curved tip, slightly smaller than propodus, longer than dactyli of P2, P3, P5, ventral margin with long fine setae, few short setae also present on dorsal distal margin of curved tip. P5 more slender than P2–P4, all articles similar in shape to those of P2, P3; except longer sickle-like dactylus, dactylus much longer than those of P2and P3 but shorter than that of P4, few long setae present on distal half of ventral (inner) margin. Relative length of ambulatory legs P4>P3>P2>P5 and dactyli of longer pereopods P4>P5>P3>P2 ( Figs. 3A–D ; A’–C’).

Pleon wide ( Fig. 1C ), with six free somites and telson, margin with tomentum, pleonal somites increasing in length distally, widening from somite 1 to 4, then decreasing towards telson.

Male: carapace subovate ( Fig. 2A ), slightly longer than wide, dorsal surface smooth, front projecting anteriorly, emarginated, eyes visible in dorsal view. MXP3 as in female. Chela stouter than in female, dorsal and ventral margins strongly convex ( Fig. 2B ), inner margin of fingers with long setae, outer surface without setae, cutting edges of both fingers same as female chela. Ambulatory legs symmetrical, length of ambulatory legs P4>P3>P2>P5 ( Figs. 3E–H ). P2–P4 with a fringe of long swimming setae on outer face of carpus and propodus increasing in size distally. P5 with propodus ellipsoidal, dactylus very curved, ventral margin of both with long setae. Relative length of dactyli of ambulatory legs P5>P4>P3>P2. Pleon with six free somites and telson ( Fig. 2C ), widest at somites 2, 3, decreasing towards evenly rounded telson. G1 long ( Fig. 2D ), sharply curved, with short angular tip, ventral surface with long setae; G2 ( Fig. 2E ) stout with pointed angular tip, exopod absent.

Host. The specimens of A. shahi n. sp. were collected from the oyster, Crassostrea madrasensis (Preston, 1916) .

Distribution. So far known only from the coastal waters of Pamban, Gulf of Mannar, Tamil Nadu state, India.

Etymology. The new species is named in honor of Professor Raman Vadilal Shah, former Head of the Department of Zoology, The Maharaja Sayajirao University of Baroda, in Vadodara, Gujarat, India, for his valuable contributions in the field of zoology.

Remarks. On the basis of the relative lengths of the dactyli of the longer P4 and P5, it is possible to recognize two subgroups within the genus Arcotheres . The larger subgroup, contains 23 species: viz. A. alcocki (Rathbun, 1909) , A. acrophilus ( Bürger, 1895) , A. atrinae (Sakai, 1939) ; A. borradailei (Nobili, 1905) , A. casta Antony & Kuttyamma, 1971 , A. coarcatus ( Bürger, 1895) , A. cyclinus (Shen, 1932) ; A. exiguus ( Bürger, 1895) , A. guinotae Campos, 2001 , A. latifrons ( Bürger, 1895) , A. latus ( Bürger, 1895) , A. modiolicola ( Bürger, 1895) , A. nudifrons ( Bürger, 1895) , A. palaensis ( Bürger, 1895) , A. placunae ( Hornell & Southwell, 1909) , A. purpureus (Alcock, 1900) , A. rhombifer ( Bürger, 1895) , A. ridgewayi (Southwell, 1911) , A. rotundatus ( Bürger, 1895) , A. similis ( Bürger, 1895) , A. sinensis (Shen, 1932) , A. spinidactylus ( Gordon, 1936) and A. tivelae ( Gordon, 1936) ( Bürger1895; Hornell & Southwell 1909; Gordon 1936; Ahyong & Ng 2007; Ng et al. 2017). The smaller subgroup contains only three species — A. pernicola ( Bürger, 1895) , A. winckworthi ( Gordon, 1936) and A. rayi Ahyong & Ng, 2007 (Campos 2001) . Arcotheres shahi n. sp. belongs to the smaller subgroup on the basis of the relative lengths of the dactyli of the P4 and P5.

Arcotheres shahi n. sp. differs from A. pernicola ( Bürger, 1895) (from Ubay, northeastern Bohol, Philippines) in the following characters: in the female, the carapace is subtrapezoidal ( Fig. 1A ) (vs. subquadrate in A. pernicola ; cf. Ahyong & Ng 2007; fig. 10F), the front is slightly produced ( Fig. 1A ) (vs. not produced in A. pernicola ; cf. Ahyong & Ng 2007; fig. 10F), the flagellum of the MXP3 exopod has three articles before aesthetascs ( Fig. 1F ) (vs. only two articles in A. pernicola ; cf. Ahyong & Ng 2007: fig. 10G), the dactylus of the P1 chela is more than half the length of the palm ( Figs. 1D, E ) (vs. dactylus is half the length of the palm in A. pernicola ; cf. Ahyong & Ng 2007: fig. 10A), the pollex has two large proximal teeth and is covered with long setae ( Figs. 1D, E ) (vs. with single large proximal tooth, pollex glabrous in A. pernicola ; cf. Ahyong & Ng 2007: fig. 10A), the dactylus of the longer P4 is 1.26 times longer than the dactyli of the longer P5 ( Figs. 3C, D ) (vs. dactylus of the longer P4 about twice as long as dactyli of longer P 5 in A. pernicola ; cf. Ahyong & Ng 2007: fig. 10E, F), and the dactyli of the P2 and P3 are conical and terminally hooked ( Figs. 3A, B ) (vs. conical but not hooked terminally in A. pernicola ; cf. Ahyong & Ng 2007: fig. 10B, C).

Arcotheres shahi n. sp. differs from A. winckworthi ( Gordon, 1936) (from Penang, Malaysia) (known only from females) in the following characters: the posterolateral margin of carapace is gently convex (vs. posterolateral margin concave in A. winckworthi ; cf. Gordon 1936: fig. 7a), the chelae are globose, with the palm’s height about 1.7 times its length ( Figs. 1D, E ) (vs. chelae slender, palm height being about 2.4 times its length in A. winckworthi ; cf. Gordon 1936: fig. 7c), the relative lengths of ambulatory legs are ranked as P4>P3>P2>P5 ( Figs. 3A–D ) (vs. P4>P5>P3>P 2 in A. winckworthi ; cf. Gordon 1936: fig. 7a), the propodi of the P3–P5 are without setae on the ventral margin ( Fig. 3B–D ) (vs. propodi of P3–P5 with setae in A. winckworthi ; cf. Gordon 1936: fig. 7a, d, e, f), and the dactyli of the P4 and P5 are sickle-like and the tip is not hooked ( Figs. 3 C-D) (vs. dactyli of P4, P5 sickle - like, with hooked at tip in A. winckworthi ; cf. Gordon 1936: fig. 7e, f).

Arcotheres shahi n. sp. differs from A. rayi Ahyong & Ng, 2007 (from Mariveles or Bohol, Philippines) (known only from females) in the following characters: the frontal margin of the carapace is gently convex ( Fig. 1A ) (vs. flattened in A. rayi ; cf. Ahyong & Ng 2007; fig. 11A), the cheliped palm is relatively shorter, about 1.6 times as long as the fingers ( Figs. 1D, E ) (vs. palm elongated, about twice as long as the fingers in A. rayi ; cf. Ahyong & Ng 2007; fig. 11D), the telson is rhomboidal with the proximal and distal margins convex ( Fig. 1C ) (vs. telson crescent-shaped, the proximal margin is concave and the distal margin convex in A. rayi ; cf. Ahyong & Ng 2007; fig. 11C).

Arcotheres shahi n. sp. is superficially similar to A. placunae ( Hornell & Southwell, 1909) (from Gujarat state, India), of the larger subgroup of Arcotheres , in having a subtrapezoidal carapace and having the dactylus of the MXP3 inserted on the ventral margin of the propodus and not reaching its tip. It differs in the following characters: in the female, the frontal margin of the carapace is gently convex ( Fig. 1A ) (vs. flattened in A. placunae ; cf. Hornell & Southwell 1909: fig. 5; Trivedi et al. in press: figs. 1A, 2A), the dactyli of the left P2 and P3 are glabrous ( Figs. 3A, B ) (vs. ventral margin covered with short setae in A. placunae ; cf. Trivedi et al. in press: figs. 4A, B), the propodi of the left P2–P5 are glabrous ( Figs. 3A–D ) (vs. left P2–P5 propodi ventral margin with scattered short setae distally in A. placunae ; cf. Trivedi et al. in press: figs. 4A–D), the dactylus of the left P5 has short setae only on the ventral margin distally (vs. entire dactylus covered with short setae in A. placunae ; cf. Trivedi et al. in press: fig. 4D); in the male, the carapace is subovate and longer than broad ( Fig. 2A ) (vs. subhexagonal, broader than long in A. placunae ; c.f. Hornell & Southwell 1909; fig. 1; Trivedi et al. in press; figs. 2C, 3A), the front is slightly concave medially ( Fig. 2A ) (vs. front almost flat in A. placunae ; c.f. Hornell & Southwell 1909; fig. 1; Trivedi et al. in press; figs. 2C, 3A), there is no well-marked cervical groove on the dorsal surface of the carapace ( Fig. 2A ) (vs. well-marked cervical grooves present on carapace in A. placunae ; c.f. Hornell & Southwell 1909; fig. 1; Trivedi et al. in press; figs. 2C, 3A), the dactyli of left P2, P3 are glabrous ( Figs. 3A, B ) (vs. dactyli of left P2–P5 setose on dorsal and ventral margin in A. placunae ; cf. Trivedi et al. in press; fig. 4A–D), and the G1 is strongly curved and its dorsal margin is glabrous ( Fig. 2D ) (vs. G1 gently curved with fringe setae on dorsal margin in A. placunae ; cf. Trivedi et al. in press; fig. 3D).

Figures

FIGURE 1. Arcotheres shahi n. sp., holotype, female (CL 6.13 mm, CW 6.77 mm) (ZL-AR-CR-97). A, habitus, dorsal view; B, frontal view; C, pleon and telson; D, right chela, outer view; E, right chela, inner view; F, left MXP3, inner view.

FIGURE 2. Arcotheres shahi n. sp., paratype, male (CL 3.43 mm, CW 3.30 mm) (ZL-AR-CR-98). A, habitus, dorsal view; B, right chela outer view; C, pleon and telson; D, G1, abdominal view; E, G2, abdominal view.

FIGURE 3. Arcotheres shahi n. sp., holotype, female (CL 6.13mm, CW 6.77 mm) (ZL-AR-CR-97). A- D, left P2–P5 dorsal view; A’- C’, right P2–P4 outer view. Arcotheres shahi n. sp., paratype, male (CL 3.43 mm, CW 3.30 mm) (ZL-AR-CR-98). E– H, left P2-P5, dorsal view.