Lophoplax andamanica ( Deb, 1989 ) Trivedi & Patel & Mitra & Ng, 2022

Trivedi, Jigneshkumar, Patel, Krupal, Mitra, Santanu & Ng, Peter K. L., 2022, On the identity of Myopilumnus andamanicus Deb, 1989 (Crustacea: Decapoda Brachyura: Pilumnidae) from India, Zootaxa 5194 (4), pp. 595-600 : 596-599

Lophoplax andamanica ( Deb, 1989) comb. nov.

( Fig. 1 )

Myopilumnus andamanicus Deb, 1989: 113–116 , fig. 1; Dev Roy 2008: 56, 168; Rao 2010: 196; Dev Roy & Nandi 2012: 202, 224; Rao et al. 2013: 17, 146; Maenosono 2019: 30.

Pseudocryptocoeloma andamanicus — Trivedi et al. 2018: 60; Maenosono 2019: 31.

Type material. Holotype, female (CL 9.4 mm, CW 10.3 mm) (ZSI. C 4152/2), under surface of dead coral rock in mangroves, Neil Island , South Andaman, India, 28 March 1987, coll. M. K. Dev Roy.

Comparative material. Lophoplax sculpta ( Stimpson, 1858) , male (CL 6.3 mm, CW 7.8 mm) ( ZRC 2013.172 ), Minatagawa , Urasoe City, Okinawa, Japan, 6 January 2008, coll. T. Maenosono .

Description. Carapace subquadrate, slightly broader than long; dorsal surface convex in anterior half, gently depressed in posterior half; surface covered by thick, generally spongy tomentum and long stiff setae, except for several symmetrically arranged glabrous areolets; regions distinctly demarcated: pair of large longitudinally rectangular areolets on epigastric region, protogastric region with pair of crescent-shaped areolets on posterior part; hepatic region with long medially depressed oblong areolet that stretches from base of external orbital angle to second anterolateral tooth; pair of unevenly shaped, gently curved areolets on cardiac region, intestinal region elevated, with transverse elevated swelling running parallel to posterior carapace margin; depressions covered with pubescence. Frontal margin slightly produced, gently deflexed, with 2 lobes separated by shallow median notch. Anterolateral margin with 5 teeth, including external orbital angle; external orbital angle triangular, directed anteriorly; first anterolateral tooth triangular, outer margin twice length of inner margin; second anterolateral teeth basally fused with 3 low, rounded tubercles, forming low swollen ridge-like structure that extends beyond junction of antero- and posterolateral margins smaller than first tooth with truncate tip, last 2 teeth depressed, blunt, broad, junction of anterolateral and posterolateral margins with 2 elevated ridges merging with epibranchial region; posterolateral margins slightly curved, convergent; posterior margin almost straight. Orbit large; ocular peduncle with pubescence of varying length on dorsal surface, suborbital angle triangular. Antennules wide, rectangular, folding transversely. Basal antennal article subrectangular, submobile; flagellum slender, elongate, entering orbital hiatus. Epistome relatively narrow longitudinally; posterior margin sinuous with median part broadly triangular. Endostome with oblique ridge on each half.

Third maxilliped merus squarish, outer-distal angle auriculiform; ischium rectangular, with shallow oblique sulcus; exopod relatively stout, not reaching distal edge of merus, with long flagellum.

Cheliped subequal; surfaces covered with long setae. Merus almost hidden beneath carapace in dorsal view. Carpus relatively large, surface covered with large and small nodules, inner angle obtuse. Palm outer surface covered with thick spongy tomentum and sparse long setae, and also with 4 granulated ridges running parallel to each other, inner surface smooth. Fingers longer than palm measured along upper margin, setose, outer surface granulated; dactylus with granulated ridge running parallel to upper margin, cutting edge with blunt teeth; pollex with granulated ridge running parallel to lower margin.

Ambulatory legs of right side missing. P2 of left side missing, P3–P5 moderetely stout, densely covered with tomentum; outer surfaces of P3–P5 merus, carpus and propodus eroded; carpus, propodus and dactylus with long stiff setae; P4 dactylus longer than propodus.

Female pleon with 6 free somites and telson; telson longer than sixth somite, distal margin rounded.

Remarks. Ng (1987) reviewed Lophoplax Tesch, 1918 , and recognized four species: L. bicristata Tesch, 1918 (type species, Sulawesi and Moluccas); L. sculpta ( Stimpson, 1858) ( Japan) ; L. takakurai Sakai, 1935 ( Japan) ; and L. sextuberculata Takeda & Kurata, 1984 ( Japan) (see also Sakai 1935; Takeda 1977; Takeda & Kurata 1984; Takeda & Marumura 1995). Three species previously placed in it: L. teschi Serène, 1971 (South China Sea), L. sagamiensis ( Sakai, 1935) ( Japan) , and L. granulosa ( MacGilchrist, 1905) ( India) , were referred to Serratocoxa Ng, 1987 . Serratocoxa is now a junior subjective synonym of Cryptolutea Ward, 1936 (also see Ng & Davie 1991; Davie & Humpherys 1997; Ng & Huang 2002). Takeda & Kurata (1984) also suggested transferring Pseudocryptocoeloma symmetrinudus Edmondson, 1951 (type locality Samoa) to Lophoplax as the taxon had eight prominent and symmetrically arranged areolets on the carapace; but they did not formally do so.

The re-examination of the holotype specimen of Myopilumnus andamanicus Deb, 1989 , showed that the species should be referred to Lophoplax , with Myopilumnus Deb, 1989 , becoming a junior subjective synonym of Lophoplax Tesch, 1918 . It has all the characters of the genus as discussed above. Lophoplax andamanica can be easily differentiated from L. bicristata , L. sextuberculata and L. takakurai in having relatively shorter and stouter ambulatory legs ( Tesch1918; Sakai 1935; Takeda & Kurata1984; Takeda &Marumura 1995). Lophoplax andamanica most closely resembles L. sculpta in having eight symmetrically arranged areolets on the carapace but differs in the following characters: epigastric region with quadrilateral areolets ( Fig. 1A ) (versus oblong in L. sculpta ; Fig. 2A, B ; Maenosono 2019: fig. 9A, B); protogastric region with elongated crescent shape areolets ( Fig. 1A ) (versus ovate or only a short crescent in L. sculpta ; Fig. 2A, B , Maenosono 2019: fig. 9A, B); hepatic region with centrally depressed oblong areolets on each side (versus evenly swollen oblong in L. sculpta ; Fig. 2A, B ; Maenosono 2019: fig. 9A, B); first three anterolateral teeth are broad with the tips blunt (versus triangular with acute tips in L. sculpta ; Fig. 2A, B ; Maenosono 2019: fig. 9A, B); the last two anterolateral teeth are broad and partially fused (versus broad and not fused in L. sculpta ; Fig. 2A, B ; Maenosono 2019: fig. 9A, B); the front is slightly deflexed ( Fig. 1B ) (versus strongly deflexed in L. sculpta ; Fig. 2D ; Maenosono 2019: fig. 9C); the epistome is slightly narrower longitudinally (versus slightly wider in L. sculpta ; Fig. 2D ; Maenosono 2019: fig. 9C); the outer surface of the carpus of the cheliped is covered with many large and small nodules ( Fig. 1C ) (versus with only four large nodules in L. sculpta ; Fig. 2F ); the cheliped fingers are sharply bent downwards ( Fig. 1D ) (versus fingers not distinctly bent in L. sculpta ; Fig. 2F ; Maenosono 2019: fig. 9D); and the outer surface of the P3–P5 merus, carpus and propodus are relatively more eroded (versus smoother in L. sculpta ; Figs. 2H–J ). Noteworthy is that L. andamaica is the first species of this genus to be recorded from the Indian Ocean; all its congeners are western Pacific in distribution.

The development and arrangement of the carapace areolets varies among the known species of Lophoplax . In L. takakurai , the carapace is almost devoid of areolets, with only rounded clusters of granules present on the protogastric and epibranchial regions ( Sakai 1935: pl. 7 fig. 2; Sakai 1976: pl. 191 fig. 4). In L. sextuberculata , L. sculpta L. andamanica and L. bicristata , the carapace has 4–13 areolets depending on the species. All five species, however, share hexagonal carapaces with the anterolateral teeth distinct; and the ambulatory legs are relatively long. We do not fully agree with Takeda & Kurata’s (1984) transfer of Pseudocryptocoeloma symmetrinudus to Lophoplax mainly because its carapace is transversely ovate, the anterolateral margin only has very low, broad lobes (not teeth) and the ambulatory legs are very short. We have examined the holotype male of Pseudocryptocoeloma symmetrinudus preserved in the Bishop P. Museum, Hawaii, it agrees very well with the redescription and figures in Maenosono (2019: 32, figs. 8B, 10, 13B, 14K, L). The taxonomy of Pseudocryptocoeloma is problematic because the type species, P. parvus Ward, 1936 (from Queensland, Australia) is poorly known despite being described from 28 males and 26 females. The original description is relatively brief but noteworthy is that Ward (1936) states that the posterior and median parts of the dorsal surface of the carapace are flat, smooth and glabrous; and the anterolateral margin is only obscurely dentate. The smoothness of the dorsal carapace surface and the absence of any mention of areolets suggest that P. parvus and P. symmetrinudus are not congeneric. However, resolution of the generic affinities of the two species must await re-study of the types of P. parvus .

Figures

FIGURE 1. Lophoplax andamanica (Deb, 1989), Holotype (CL 9.4 mm, CW 10.3 mm) (ZSI. C 4152/2), Neil Island, South Andaman, India. A, carapace dorsal view; B, frontal view; C, right chelipeds, dorsal view; D, chela, outer view; E, pleon; F, left P3, dorsal view; G, left P4, dorsal view; H, left P5, dorsal view. Scale bar = 1.0 mm.

FIGURE 2. Lophoplax sculpta (Stimpson, 1858), male (CL 6.3 mm, CW 7.8 mm) (ZRC 2013.172), Japan.A, dorsal habitus; B, carapace, dorsal view; C, left third maxilliped, dorsal view; D, frontal view; E, chela, outer view; F, right chelipeds, dorsal view; G, right P2, dorsal view; H, right P3, dorsal view; I, right P4, dorsal view; J, right P5, dorsal view.