Plagusia squamosa ( Herbst, 1790 )

Naderloo, Reza, 2011, Grapsoid crabs (Decapoda: Brachyura: Thoracotremata) of the Persian Gulf and the Gulf of Oman, Zootaxa 3048, pp. 1-43 : 36-40

Plagusia squamosa ( Herbst, 1790)

( Figs. 17 a–f, 18e–f)

Cancer squamosus Herbst, 1790: 260 –261, pl. 90, fig. 113.

Plagusia squamosa — H. Milne-Edwards 1837: 94. — Nobili 1906b: 324. —Schubart & Ng: 2000, 327, fig. 3. — Ng et al. 2008: 218 (list). — Castro 2011: 119 (list).

Plagusia tuberculata Lamarck 1818: 247 . — Holthuis 1977: 176. — Vannini & Valmori 1981: 92, figs. 25A, 26A, 27. — Hogarth 1989: 113. — Dai & Yang 1991: 561 (in key), 562–563, pl. 73 (5), fig. 293 (2). — Tirmizi & Ghani 1996: 148 –150, fig. 57. — Apel 2001: 120.

Plagusia depressa var. squamosa — Alcock 1900: 438.

Plagusia depressa tuberculata — Kemp 1915: 241. — Rathbun 1918: 334, pl. 102. — Tesch 1918: 129. — Sakai 1939: 702, pl. 109, fig. 4; 1965: 206, pl. 206, fig. 1. — Tweedie 1950: 136. — Barnard 1950: 134. — Chhapgar 1957: 61, pl. 16. — Edmondson 1959: 190, figs. 22a, 23 a–c. — Crosnier 1965: 80, pl. 7. fig. 3.

Plagusia depressa — Sakai 1999: 39, pl. 21C.

Type locality. East Indies ( Plagusia squamosa Herbst, 1790 ), Mauritius ( P. tuberculata Lamarck, 1818 ), Indo- West Pacific ( P. orientalis Stimpson, 1858 ).

Material examined. GULF OF OMAN, Iran: 2 males ( ZUTC Brach1133), rocky/cobble, Ramin, Baluchestan, 25º 16'N, 60º 44'E, coll. R. Naderloo, 18.11.2005. UAE: 4 males, 6 females ( SMF 26094) Abu Ahmad, Fujairah, 25º 10'N, 56º 28'E, coll. M. Apel, 0 2.07.1995. ARABIAN SEA: Oman: 1 male, 1 female ( SMF 26093), Ras Madrakah, 18º 58.6'N, 134º 10.6'E, rocky, coll. M. Apel, 02.01.2001 (labelled as P. tuberculata ). Red Sea: 1 female ( SMF 5394), (labelled as P. squamosa ). INDIAN OCEAN, Kenya: 1 female ( SMF 37730), Kilifi, coll. Baumeister, Dec.1985 (labelled as P. tuberculata ). PACIFIC OCEAN, Japan: 2 males ( SMF 35354), Kochi, 33º 16.6'N, 134º 10.6'E, coll. K. Matsuzawa, 22.05.1990, (labelled as P. tuberculata ); 3 males, 1 female ( SMF 35355), 33º 16.6'N, 134º 10.6'E, coll. K. Matsuzawa (labelled as P. tuberculata ). Taiwan: 1 female ( SMF 26093), Pingdong, coll. H.-C. Liu, 0 1.02.1999 (labelled as P. squamosa ).

Redescription. Carapace subcircular ( Figs. 17 a, 18e), slightly broader than long, about 1.06 times as broad as long, maximum breadth slightly behind middle part of carapace; carapace moderately convex; granule-shaped tubercles over carapace, posteriorly getting flattened, short setae densely surrounding anterior margin of tubercles; 2 faint oblique ridges on posterolateral regions of carapace, short one in front of them. Lateral margin of carapace arched; 4 anterolateral teeth (including exorbital tooth), sharply triangular, widely separated from each other, smaller posteriorly. Frontal lobe separated from inner orbital angle by deep U-shaped notch, with margin weekly granular; 2 distinctly high granules on frontal region; deep furrow running from anterior part of frontal lobe posteriorly, distinctly dividing frontal lobe. Orbits deep, supraorbital margin elevated, distinct notch separating inner margin from lateral margin, large granule on anterior part of inner margin; inferorbital margin elongately triangular in inner part, few small granules on outer part; eyestalks short, widen proximally, depressed medially; dense setae on anterior surface of depression, continuing distally to end of cornea.

Epistome with 7 truncated lobes, median one largest. Third maxilliped nearly long, ischium about two times as long as merus; dense brown setae along inner margin of ischium, merus, row of short setae on outer surface of ischium running along proximal two-thirds of inner margin; narrow longitudinal furrow medially along outer surface of ischium; wide depression on outer surface of merus, widening distally; exopod not reaching to middle part of merus.

Chelipeds subequal, relatively small compared to walking legs; row of short setae along inner surface of ischium, continuing to inner surface of merus. Merus with distinct distal spine on upper margin; inner margin with small granules, with large distal one; distal margin with 2 or 3 large teeth. Carpus granular on outer surface, with 4 curved furrows, covered with short dense setae; large triangular tooth medially on inner margin. Manus ( Fig. 17 b) granular over much of its surface; outer surface with low granules, 3 weak rows of granules along middle part; lower margin with relatively larger granules; upper margin with 4 rows of large granules, inner row with toothshaped granules, furrows with dense short setae; inner surface medially swollen, large granules over most of inner surface. Movable finger curved downward, large granules proximally on upper, inner surface; 2 furrows with short setae. Movable finger short, with few small granules on lower margin; cutting edge of finger with large truncate teeth, smaller distally; small gap between fingers; tips of fingers spoon-shaped.

Walking legs relatively long, moderately flattened. Merus posterior surface with transverse ridges, dense covered with short setae; longitudinal row of small denticles near anterior margin, denticles larger distally; rows of dense setae along upper surface, setae sparse on first walking leg; anterior margin of merus with relatively long setae, with large subdistal spine; long ridge near posterior margin, with long setae as on inner margin; merus of third leg about 2 times as long as broad. Carpus with 2 rows of long setae on upper surface, with row of short setae between them. Propodus slightly longer than carpus, with row of dense long setae along anterior margin, 2 rows of short setae on posterior surface, one row of short setae along anterior surface. Dactylus with row of long setae on posterior surface near anterior margin; 2 rows of about 5 spines along posterior margin; dactylus ending with large spine.

Male abdomen ( Fig. 17 c) triangular; fifth somite longest, slightly longer than sixth, sixth with lateral margin converging distally, slightly sharply converging on distal two-thirds; telson clearly triangular, strongly converging on distal half.

G1 ( Fig. 17 d) moderately stout, nearly straight; slightly tapering distally; sperm channel spiral; apical chitinous process ( Fig. 17 e) small, directed outwards at 60º angle, apically V-shaped; gonopore terminal; smooth setae densely around apical part, fully obscuring chitinous process.

Female gonopore ( Fig. 17 f) on tip of markedly elevated part, transversely on anterior face of elevation.

Remarks. The taxonomic history of Plagusia is intricate. A detailed taxonomic history of the genus was given by Schubart & Ng (2000) and Schubart et al. (2001). Schubart & Ng (2000) regarded the type specimen of P. squamosa (Herbst, 1818) in the Berlin Zoological Museum, which had been photographed by Sakai (1999: fig. 21C) as the senior synonym of P. tuberculata Lamarck, 1818 . Ng et al. (2008) followed Schubart & Ng (2000). Material of P. tuberculata and M. squamosa from different Indo-West Pacific locations deposited in SMF (see Material Examined) using mainly the features of G1 and female gonopore was examined. All specimens belong to the same species, therefore the synonymy of these three species by Schubart & Ng (2000), with priority given to P. squamosa ( Herbst, 1790) is followed.

Biology. Plagusia squamosa is a medium-size species (largest male CL = 32.48 mm, CB = 34.72 mm, largest female CL = 38.30 mm, CB = 39.20 mm) which is common in the Gulf of Oman where large populations are found on the splash zone of exposed rocky shores. It is sympatric with G. albolineatus in this habitat. Plagusia squamosa can also be seen clinging on drifting debris, oil platforms, buoys and ship hulls, which explains the species wide distribution by anthropogenic activities (see Schubart et al. 2001).

Colour. Posterior surface of the carapace and appendages is light brown, inferior surface bright. Tips of the fingers and distal part of the walking legs dactylus are bright brown.

Regional records. GULF OF OMAN: east coast of UAE ( Apel 2001); Iran (present study). There is no record from the Persian Gulf.

Geographical distribution. Indo-West Pacific: South Africa, Madagascar, Comoros, Mauritius, East Africa, Somalia, Red Sea, Gulf of Aden, Oman, Gulf of Oman, Pakistan, India, China, Japan, Australia, New Zealand, Hawaii, and recently from Mediterranean by Zaouali et al. (2007) and eastern Pacific by Castro (2011).

Figures

FIGURE 17. Plagusia squamosa (Herbst, 1790), male (ZUTC Brach 1133): a – e; female (SMF 26094): f. a, posterior surface of carapace; b, cheliped of male, outer surface; c, male abdomen; d, G 1, ventral surface (left); e, apical part of same G 1; f, female gonopore (right).