Eucrate indica, Castro & P. K. L. Ng, 2010

CASTRO, PETER & NG, PETER K. L., 2010, Revision of the family Euryplacidae Stimpson, 1871 (Crustacea: Decapoda: Brachyura: Goneplacoidea), Zootaxa 2375 (1), pp. 1-130 : 32-35

Eucrate indica n. sp.

( Figs. 2D ; 4D–F ; 9A–F ; 15A–C)

Eucrate alcocki — Ng & Davie 2002: 378 [Andaman Sea coast of Thailand]. — Rajkumar et al. 2009: 832, fig. 1 [ India]. (not Eucrate alcocki Serène , in Serène & Lohavanijaya, 1973)

(?) Eucrate crenata var. dentata — Alcock 1900: 299 [in key], 301 [ India]. — Sankarankutty 1966: 350 [in list; India].

Type material. Male holotype, 23.8 mm × 28.4 mm ( ZRC 2001.1058 ; Figs. 4E , 9 , 15A–C); 1 female paratype, 17.6 mm × 20.8 mm ( ZRC 1999.0135 ), 1 male paratype, 20.1 mm × 24.2 mm, 1 female paratype, 20.0 mm × 24.2 mm ( ZRC 1998.1119 ), 1 male paratype, 18.1 mm × 21.8 mm, 1 female paratype, 13.5 mm × 17.1 mm ( ZRC 2001.1058 ) .

Type locality. Thailand, Andaman Sea coast, Phuket I. fishing port

Material examined. India. Tamil Nadu, fish landing opposite Vellar estuary, A. S. Fernando & P. K. L. Ng coll., 24.03.2001: 1 male, 22.3 mm × 27.3 mm, 1 female, 22.8 mm × 28.3 mm ( ZRC 2001.0867 ) . – Chennai [Madras], Kasimedu fishing port, shrimp trawlers, Z. Jaafar coll., 23.11.2004: 1 male, 21.5 mm × 26.7 mm, 1 ovigerous female, 18.5 mm × 23.1 mm ( ZRC 2004.0764 ) . – Bay of Bengal , D. Rajkumar leg., 06.2006: 1 male, 23.8 mm × 29.1 mm ( MNHN-B30155 ) .

Thailand. Andaman Sea , Phuket I., Pichai fishing port, P. K. L. Ng coll., 04.1997: 1 female paratype, 17.6 mm × 20.8 mm ( ZRC 1999.0135 ) . – N. K. Ng et al. coll., 17– 20.01.2000: carapace, 18.6 mm × 23.2 mm ( ZRC 2000.0764 ) . – Phuket I. fishing port, S. Chaitiamwong et al., 1 male paratype, 20.1 mm × 24.2 mm, 1 female paratype, 20.0 mm × 24.2 mm ( ZRC 1998.1119 ) . – Phuket I. fishing port, P. K. L. Ng et al. coll., 17.02.2001: male holotype, 23.8 mm × 28.4 mm, 1 male paratype, 18.1 mm × 21.8 mm, 1 female paratype, 13.5 mm × 17.1 mm ( ZRC 2001.1058 ) .

Peninsular Malaysia. Andaman Sea Coast, between Penang and Langkawi, trawling, C. P. How & C. O. Lau coll., 12.11.1991: 1 female, 15.3 mm × 19.0 mm ( ZRC 1992.10458 ) .

Diagnosis. Third anterolateral tooth absent or reduced as slight elevation, carapace with relatively long posterolateral borders ( Figs. 2D ; 4D–F ; 9A ). P5 propodus slender ( Figs. 2D ; 9A ). Irregular, large, red-brown spots on median portion of carapace ( Figs. 2D ; 4D–F ; 9A ).

Description. Carapace ( Figs. 2D ; 4D–F ; 9A ) transversely hexagonal, wider than long (1.19 wider than long in male holotype), anterolateral borders arched, dorsal surface without clear indication of regions; front wide, with median notch, deep transverse sulcus along margin. Three anterolateral teeth posterior to short, triangular outer orbital tooth (first short, triangular, obtuse tip; second largest, slender, acute; third short, barely noticeable). Orbits short ( Fig. 9C ), shorter than front (0.6 frontal width in holotype), conspicuous notch between front, orbit; conspicuous notch on median portion, shallower notch on outer portion of curved, thick supraorbital border; suborbital border ( Fig. 9B ) sinuous, with short, obtuse inner suborbital tooth, short median lobe; eye peduncles short (0.2 frontal width in holotype), as long as corneas; large, spherical corneas. Basal antennal article slightly immobile, with disto-lateral process so that orbital hiatus is closed excluding antennal flagellum from orbit.

Posterior margin of epistome lobular; lateral lobes large, with sinuous margins, separated from median portion by deep fissure; median portion with 2 lobes separated by deep fissure ( Fig. 9C ). Anterior margin of endostome well demarcated from buccal cavern, endostomial ridges low. Pterygostomian region with low granules. Third maxillipeds ( Fig. 9B ) completely closing buccal cavern; ischium rectangular with deep submedian line; merus relatively square in shape but anteroexternal part angular, rounded; exopod long, reaching to just before anterior edge of merus with long flagellum.

Cheliped fingers ( Fig. 9D ) moderately stout, slightly longer than swollen propodus, distal portion light in colour. Inner (dorsal) margin of carpus with large tooth; short tomentum on anterior margin of carpus; outer (dorsal) margin of merus with large, obtuse tooth, row of short tubercles. Dorsal, ventral margins of ambulatory legs (P2–P5) with short tubercles, dorsal margins of carpus with long, simple setae; dactyli long, slender; P5 merus ( Fig. 9A ) long, moderately slender (16.2 mm long in holotype), ventral margin slightly curved, distal end reaches past third anterolateral tooth but not second anterolateral tooth when folded against carapace; P5 propodus (9.8 mm long, 3.0 mm wide in holotype), proportionally stout, subcylindrical; inner, outer margins fringed with row of numerous short, simple setae; P5 dactylus (9.5 mm long, 2.0 mm maximum width in holotype) proportionally slender, subcylindrical, fringed with short, simple setae.

Thoracic sternum ( Fig. 9E ) wide, thoracic suture 2/3 complete, convex; 3/4 deep, short, interrupted; 4/5, 6/7, 7/8 interrupted, 5/6 complete; median groove on thoracic sternites 7, 8. Sterno-abdominal cavity of male deep, nearly reaching anterior margin of sternite 4. Press-button of male abdominal-locking mechanism as tubercle near thoracic suture 4/5.

Male abdomen ( Fig. 9E ) narrow, slender (T-shaped), lateral margins of somites 4–6 abruptly narrowing from somite 3 to transversely narrow, pointed telson; somite 3 reaching inner margins of P5 coxae ( Fig. 9F ); no portions of thoracic 8 exposed by closed abdomen, somite 2 slightly transversely shorter than somite 3. G1 long, slender, sinuous, acuminate apex, with small denticles ( Figs. 15A, B); G2 ( Fig. 15C) less than one-third of G1, straight, with 2 processes: one long, tip obtuse; second much shorter, tip acute. Male genital opening (gonopore) coxal; coxo-sternal disposition of long penis, protected by concave posterior portion of thoracic sternite 7.

Vulva ovoid, extending across anterior portion of sternite 6 close to median axis of thorax; covered by soft membrane, sternal vulvar cover absent.

Colour pattern. Two large, irregular, red-brown spots on the median portion of the dorsal surface of the carapace, each flanked by two smaller, vertically placed spots ( Figs. 2D ; 4D–F ; 9A ; see Remarks below). The central or lateral spots may coalesce into a single lateral spot ( Fig. 4E ). All spots may also coalesce, forming irregular patterns bearing a striking resemblance to letters or numbers ( Fig. 2D ). Small red-brown spots are located along the anterior border of the carapace and dorsal surface of chelipeds.

Etymology. Indica from India and Indian Ocean, to denote the distributional range of this species in contrast to two similar species, Eucrate alcocki in China and southwestern Asia, and E. formosensis in Taiwan.

Remarks. The populations that had been identified as “ E. alcocki ” from the Indian and western Pacific oceans are clearly different in their carapace colour patterns. In true E. alcocki from China, Vietnam, Gulf of Thailand and Singapore, there are consistently one to six large spots or blotches on the median portion of the carapace, and the anterior portion has numerous smaller spots ( Figs. 2C ; 4A, B ). In specimens from the Indian Ocean and as far west as the Andaman Sea coast of Thailand and the northern Straits of Malacca (Phuket I., Langkawi, and Penang islands), there are usually six large spots arranged transversely across the median portion of the carapace and numerous smaller spots on the anterior portion of the carapace. This colour pattern is consistent for the large series of specimens examined.

There are also several morphological differences. Specimens from the Indian Ocean have proportionately wider carapaces (width to length ratio 1.18–1.26, n = 13, mean = 1.21; 1.09–1.29, n = 32, mean = 1.16 in E. alcocki ) ( Figs. 2D , 4D–F for E. indica ; Figs. 2C , 4A, B for E. alcocki ), the frontal margin is generally more prominent, well produced, and with a distinct median notch ( Figs. 4D–F ; 9C ) (less prominent, with the median notch shallow or barely visible in E. alcocki , Figs. 4A–C ), the cleft between the frontal margin and inner suborbital tooth is deep and pronounced ( Fig. 9C ) (shallow in E. alcocki ), and the supraorbital border has a deep and prominent notch ( Figs. 4D–F ; 9C ) (shallow and less distinct in E. alcocki , Figs. 4A–C ). As such, we are of the opinion that the Indian Ocean material should be referred to as a separate species.

As has been discussed earlier under E. alcocki , the record of Eucrate crenata var. dentata by Alcock (1900: 299, 301) from India (see also list of Indian taxa in Sankarankutty 1966: 350) may be Eucrate indica n. sp. as well. Serène & Lohavanijaya (1973) had suggested it may be E. alcocki .

The geographic distributions of E. indica n. sp. and E. alcocki are noteworthy as, E. indica n. sp. is found in the Persian Gulf, Indian Ocean, and the Andaman Sea, whereas E. alcocki is found on the Gulf of Thailand and the western Pacific Ocean. A similar pattern has also been observed for several other species of brachyurans, with one species occurring in the Indian Ocean (e.g. the xanthid Liagore erythematica Guinot, 1971 , the calappid Calappa bilineata Ng, Lai & Aungtonya, 2002 , the portunid Portunus reticulatus (Herbst, 1799)) and a close species present in the Pacific ( Liagore rubromaculata (De Haan, 1835) , Calappa philargius (Linnaeus, 1758) , Portunus pelagicus (Linnaeus, 1758) , respectively) (see Ng et al. 2002; Ng & Chen, 2004; Ng et al. 2008; Lai et al. 2010).

Distribution. Persian Gulf, India, Andaman Sea coasts of Thailand and Peninsular Malaysia. Depth: shallow subtidal.

Figures

FIGURE 2. Fresh colours of Eucrate species. A, B, E. crenata (De Haan, 1835); A, male (22.5 mm × 27.1 mm) (ZRC 2002.0493), China, Qingdao; B, male, Hong Kong, not preserved; C, E. alcocki Serène, in Serène & Lohavanijaya, 1973, ovigerous female (18.4 mm × 21.4 mm) (ZRC 2003.0621), Thailand, Pattani, Thailand; D, E. indica n. sp., female, Persian Gulf, not preserved; E, F, E. formosensis Sakai, 1974; E, female (22.2 mm × 27.1 mm) (ZRC 1993.739), Taiwan, Kaohsiung, Taiwan; F, juvenile, northern Taiwan, not preserved. Photo credits: B by D. Poon; D by R. Naderloo (Forschunginstitut Senckenberg, Frankfurt); E by K. Li.

FIGURE 4. Variation in colour patterns of carapace of Eucrate species. A–C, Eucrate alcocki Serène, in Serène & Lohavanijaya, 1973; A, female (15.1 mm × 17.7 mm) (ZRC 2003.0605), Gulf of Thailand; B, male (19.2 mm × 23.3 mm) (ZRC 1998.1055), Gulf of Thailand; C; male paratype of Eucrate maculata Yang & Sun, 1979 (= E. alcocki) (15.9 mm × 18.7 mm) (BMNH J79139), China, Fujian Province, Dongshan; D–F, Eucrate indica n. sp.; D, male (22.8 mm × 28.3 mm) (ZRC 2001.0867), India, Tamil Nadu, fish landing opposite Vellar estuary; E, male holotype (23.4 mm × 28.3 mm) (ZRC 1998.1058), Thailand, Andaman Sea, Phuket I.; F, female (22.8 mm × 28.3 mm) (ZRC 2001.0867), India, Tamil Nadu, fish landing opposite Vellar estuary.

FIGURE 9. Eucrate indica n. sp.; male holotype (23.8 mm × 28.4 mm) (ZRC 1998.1058), Thailand, Andaman Sea, Phuket I. A, overall view; B, third maxillipeds, antennules, antennae, and orbits; C, frontal view; D, outer surface of right chela; E, anterior portion of male thoracic sternum and abdomen; F, posterior portion of male thoracic sternum and abdomen. Abbreviations: a1–a3 = male abdominal somites 1 to 3, respectively; cx5 = coxa of fifth pereopod (P5); t = telson.