Parilia alcocki Wood-Mason, in Wood-Mason & Alcock 1891
Creators: name: Prema, M.
name: Ravichandran, S.
name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2018
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Leucosiidae
Parilia
Parilia alcocki

description: Parilia alcocki Wood-Mason, in Wood-Mason & Alcock, 1891
(Figs. 1, 2, 4A–D, F, 5A–G)
Parilia alcocki Wood-Mason, in Wood-Mason & Alcock 1891: 264; Wood-Mason 1892: pl. 5 figs. 3, 3a; Alcock & Anderson 1894: 177; Alcock 1896: 198; Alcock 1899: 28, pl. 4 fig. 1; Tirmizi & Serène 1971: 30, text fig. 4; Ng et al. 2008: 92; Krishnamoorthy 2009: 2; Huys et al. 2014: 16; Lakshimi Pillai et al. 2013: 72, unnumbered colour figure. Paralia (sic) alcocki— Lloyd 1907: 3.
Material examined. 14 males (largest 70.6 × 52.2 mm, smallest 43.0 × 36.5 mm), 10 ovigerous females (largest 47.4 × 38.8 mm, smallest 41.2 × 34.4 mm) (CASAU), 1 male (66.1 × 57.4 mm), 2 ovigerous females (45.2 × 37.0 mm, 41.5 × 35.6 mm) (ZRC 2017.0215), Pazhayar fish landing center, 11º21'30.28"N 79º49'39.83''E, Tamil Nadu, India, 549 m, coll. M. Prema, 14 March 2017; 1 young male (24.8 × 23.4 mm) (ZRC 2017.0216), fishing port, Tuticorin, Tamil Nadu, India, coll. A. B. Kumar et al., March 2017.
Comparative material. Parilia major Sakai, 1961 — 1 male, 2 females (ZRC 2001.0050), Su-Ao Port, Nangfangao, northeastern Taiwan, coll. P. K. L. Ng, 5 November 2000; 1 male, 3 females (ZRC 2017.0217), station PN1, Balicasag Island, Panglao, Bohol, Philippines, coll. P.K.L. Ng from fishermen, June 2004; 7 males, 4 females, 2 ovigerous females (ZRC 2001.552), Panglao, Bohol, Philippines, coll. fishermen, 28 November 2001; 10 males, 5 females (ZRC 2017.0218), Maribojoc Bay, Panglao, Bohol, Philippines, coll. J. Arbasto, November 2003 — April 2004. Parilia ovata Chen, 1989 — 1 male (ZRC 2017.0219), northwestern Panglao, Bohol, Philippines, coll. J. Arbasto, 2006.
Description of adult male. Carapace transversely subovate, almost subhexagonal in shape, distinctly broader than long; surface covered with numerous small granules (more prominent in larger specimens); hepatic region (adjacent to anterolateral margin) swollen; gastric and branchial regions distinctly inflated; dorsal surface strongly convex, convexity more pronounced posteriorly; oblique cervical groove shallow but clearly visible, with 3 deep pits along posterior half; cardiac region swollen, with prominent posteriorly directed tooth, separated from gastric and branchial regions by deep grooves; gastro-cardiac groove deep, prominently separating cardiac and intestinal regions from swollen branchial regions, prominent tubercle present at junction of groove between anterior part of cardiac region and branchial region; low but distinct median longitudinal ridge present from gastric to cardiac region; intestinal region low, pushed behind by swollen cardiac region, not well defined; carapace appears box-like from frontal view (Figs. 1A, 2A, 4D, F). Antennae with short flagellum, not extending beyond orbit. Antennules folding obliquely (Fig. 2B). Orbit small, rounded; eye with short peduncle; supraorbital margin with 2 prominent fissures; suborbital margin with distinct low tooth on inner margin (Figs. 2B, 4D, F). Epistome wide, median part projecting anteriorly, with deep median fissure; lateral part of epistome visible from dorsal view; endostomial ridge strong, longitudinal (Figs. 2B, 4D, F).
Frontal margin distinct not produced anteriorly, bilobed, with broadly triangular concavity separating broadly triangular lobes; not covering anteriorly protruding ptergygostomial regions, and lateral part of epistome in dorsal view (Figs. 1A, 2A, 4F). Anterior half of anterolateral margin (margin of hepatic region) set back from carapace margin, low, starting as low ridge of row of low granules from supraorbital margin, becoming more cristate along posterior half (separated by low, wide concavity) which has 3 low teeth (Figs. 2A, 4F). Pterygostomial region relatively wide, visible in dorsal view; anterior tooth adjacent to buccal cavity appears bilobed with basal part broader, separated from margin by low cleft; posterior tooth low, just before meeting anterolateral margin (Figs. 2A, 4F). Posterolateral margin strongly convex, entire except for small tooth just before posterior carapace margin (Figs. 2A, 4F). Posterior carapace margin with 2 prominent lateral sharp teeth (Figs. 2A, 4F).
Buccal cavity very wide, more than half width of carapace; prominently protruding anteriorly, edge clearly visible in dorsal view; third maxillipeds appears almost vertical in lateral view when closed (Figs. 2A, B, 4D, 5A). Third maxillipeds completely covering space when closed; surfaces with small granules; palp (carpus, propodus and dactylus) concealed behind merus when retracted, longer than merus; merus shorter than ischium, with broadly triangular distal margin, lined with setae; ischium with shallow submedian oblique sulcus; exopod foliaceous, very broad, much wider than ischium with outer margin strongly convex; main part of coxa deeply inserted into cephalothorax, external surface with very wide, almost semi-circular plate extending from base, bracketing base of wide exopod (Figs. 2B, 4D, 5A). Surfaces of sub-orbital, pterygostomial, sub-hepatic and sub-branchial regions covered with small granules; anterior margin of pterygostomial region subcristate; sub-branchial and ptergygostomial regions separated by deep oblique groove (Figs. 2B, 4D).
Chelipeds very long, slender, surfaces of merus, carpus and palm covered with small but distinct sharp granules; merus long, cylindrical, slightly bent medially; carpus short; palm subcylindrical, with distal part proportionately broader, elongated, at least twice length of carapace in largest specimens; palm more than 3 times length of slender fingers; dactylus gently curved; basal part of propodal finger arched, forming prominent gape with dactylus when closed; cutting edges of fingers (occluding surfaces) with low teeth, uneven to almost smooth (Figs. 1A, 2A, C).
Ambulatory legs long, slender; first leg longest, last leg shortest; surfaces of merus, carpus and propodus covered with small sharp granules; merus and propodus subcylindrical, not armed with spines or setae; dactylus gently curved, dorso-ventrally flattened, each dorsal margin with dense row of setae, tip rounded (Figs. 1A, 2A).
Thoracic sternum with surfaces gently pitted to smooth; sternites 1–4 completely fused, forming one plate without trace of sutures; all sutures between sternites 4–8 medially interrupted; pleonal locking mechanism consisting of projecting edges of sternites 5–7, no trace of peg or tubercle on sternite 5 (Fig. 2D). Sternopleonal cavity deep, reaching to just before groove separating thoracic sternites 2 and 3 (Fig. 2B, D). Part of thoracic 8 exposed when pleon closed, visible as small plate at anterolateral edge of somite 3 (Fig. 2D). Penis tubular, exiting on condyle of coxa of fourth ambulatory leg.
Pleon elongate, triangular, surface smooth; somite 1 and 2 free; somites 3–5 completely fused, with only short median groove indicated between somites 3 and 4, lateral margin sinuous; somite 3 widest, lateral margins reaching coxae of fourth ambulatory legs; somite 6 not fused with sternite 5, mobile, long, trapezoidal; telson free, acutely triangular (Figs. 2D, 5B). G1 elongate, basal part broadest, median and distal parts slender, tubular, almost straight from ventral view; distal part bifurcated, longer projection directed inwards towards median of thoracic sternum, distal part flared to form prominent flange, margin of flange serrulate to dentate, shorter projection almost in line with rest of G1, distal part flared with serrulate margin on flange (Fig. 5D–F). G2 short, distal segment as long as basal segment, with curved flagelliform tip (Fig. 5G).
Female. Pleon strongly convex, dome-like; somites 1–4 free, separated by deep sutures but somites barely mobile; somites 4 and 5 separated by deep suture, barely mobile; somites 5 and 6 fused, separated by shallow suture, completely immobile; telson mobile, separated from somite 6 by deep suture, triangular with concave lateral margins; surface of somites smooth (Figs. 2F, 5C). Sternopleonal cavity large, deep, with prominent rim, completely covered by pleon; sutures separating thoracic sternites 4–8 all medially interrupted, median part of cavity with large projection between thoracic sternites 5–7; vulvae on anterior edge of sternite 6, pushing into sternite 5, opening crescent-shaped, with narrow operculum, inner margin slightly raised (Fig. 2G). Eggs small, numerous, reddish-brown in life.
Variation. Small specimens tend to be relatively less inflated and the carapace is more rounded, with the teeth on the antero- and posterolateral margins, posterior carapace margin and cardiac region proportionately longer (Fig. 4A, C). As a result, the frontal and anterolateral margins are less distinctly set back, the buccal cavity and third maxillipeds do not protrude anteriorly and is gradually sloping backwards rather than almost vertical (Fig. 4A, C). The various surfaces of the carapace, third maxillipeds and chelipeds are also smoother with the granules barely discernible, and the chelipeds are proportionately shorter (Fig. 4A). The exopod of the third maxilliped is also relatively less foliaceous (Fig. 4B). Female specimens are similar to males in most non-sexual characters except that the chelipeds are proportionately much shorter (Figs. 1B, 2E).
Colour. In life, the carapace and chelipeds of adults are orange to reddish-orange, the ambulatory legs are white with parts of the merus orange, and the ventral surfaces are white (Fig. 1).
Remarks. Of the four known species of Parilia, P. tuberculata is easily separated from all congeners by its prominently tuberculated carapace and legs (Sakai 1961, 1976; Ikeda 1998); and is known thus far only from Japan. Parilia ovata can be distinguished by its distinctly elongated carapace with the cardiac spine very long (Chen 1989; Tan 1996; Chen & Sun 2002; Zarenkov 1990), and is known thus far only from the South China Sea and the Philippines. Sakai (1961, 1976), Tirmizi & Serène (1971) and Tan (1996) separated P. alcocki from P. major by its wider than long carapace with the branchial regions prominently inflated (Figs. 2A, B, 3A, E, 5D, F); the hepatic region is swollen (Fig. 5D, F); the epistome projecting clearly beyond the edge of the front (Fig. 5F); and the exopod of the third maxillipeds is foliaceous and proportionately wider (Figs. 3B, 6A) (cf. Fig. 4A–C for P. major). There are, however, more characters that separate adults of P. alcocki from P. major: the wide carapace gives P. alcocki a box-like appearance in frontal view with the branchial regions prominently swollen and the posterolateral margin strongly convex (Fig. 4D, F) (carapace dome-shaped in dorsal view with the branchial regions convex but not swollen and the posterolateral margin gently convex in P. major; Figs. 3A, B, 4E, G); the buccal cavity is so strongly produced anteriorly that it appears almost vertical in lateral view (Fig. 4D) (sloping backwards in P. major; Fig. 4E); the posterior pterygostomial tooth is distinct even in large specimens (Fig. 4F) (tooth very low to indiscernible in P. major; Fig. 4G); the surfaces of the chelipeds and ambulatory legs (merus carpus and propodus) are prominently granulate (Fig. 2A, C, E) (surfaces of chelipeds and ambulatory legs smooth in P. major; Fig. 3A, B, D); the male pleon is proportionately more slender (Fig. 2D) (male pleon transversely broader in P. major; Fig. 3E); the flange on each of the distal projections of the G1 is more pronounced with the spines more prominent (Fig. 5E, F) (flanges less prominent in P. major; Fig. 5I, J); and the female sternopleonal cavity has a prominent median projection (Fig. 2G) (entire sternopleonal cavity surface smooth in P. major; Fig. 3G).
The known distributions of the two species are distinct. Parilia major is known from Japan, Taiwan, the Philippines, Indonesia, Papua New Guinea and the Solomon Islands, at depths of 90–425 m (Sakai 1961, 1976; Chen 1989; Tan 1996; Ikeda 1998; Chen & Sun 2002; Galil 2007; Galil & Ng 2007). Parilia alcocki is known from Oman, Pakistan, and India, in depths ranging from 124 to 457 m (Wood-Mason & Alcock 1891; Alcock 1896, 1899; Lloyd 1907; Tirmizi & Serène 1971; Lakshimi Pillai et al. 2013). There is a record of a small male of “ P. alcocki ” (lacking chelipeds) from eastern Sumatra (Doflein 1904: 44), but Sakai (1961) and Tirmizi & Serène (1971) commented that the specimen more closely resembles P. major. Material from the eastern Indian Ocean was examined (PNG, unpublished data) and it is neither P. major nor P. alcocki, but likely a new species.
Lakshimi Pillai et al. (2013) suggested that P. alcocki has potential in the aquarium trade on account of its attractive colours (see also Calado et al. 2003). The keeping of deep-sea species, however, is difficult and we do not see the potential for this; not to mention the logistical issues of keeping stocks and exporting them to overseas markets. The relatively large size of this species also poses challenges.
description: Published as part of Prema, M., Ravichandran, S. & Ng, Peter K. L., 2018, Redescription of Parilia alcocki Wood-Mason, in Wood-Mason & Alcock, 1891 (Decapoda, Brachyura, Leucosiidae) from southeast India, pp. 111-120 in Zootaxa 4378 (1) on pages 112-118, DOI: 10.11646/zootaxa.4378.1.7, http://zenodo.org/record/1168150