Metopograpsus thukuhar ( Owen, 1839 )

Naderloo, Reza, 2011, Grapsoid crabs (Decapoda: Brachyura: Thoracotremata) of the Persian Gulf and the Gulf of Oman, Zootaxa 3048, pp. 1-43 : 11-14

Metopograpsus thukuhar ( Owen, 1839)

( Figs. 4 a–g, 5f)

Grapsus thukuhar Owen, 1839: 80 , pl. 24, fig. 3.

Metopograpsus thukuhar — H. Milne-Edwards 1853: 165. — Crosnier 1965: 23 (in key), 25, figs. 20, 27. — Holthuis 1977: 157, 158. — Al-Ghais & Cooper 1996: 413, fig. 3. — Tirmizi & Ghani 1996: 140, fig. 54. — Hornby 1997: 14. — Apel & Türkay 1999: 132. — Apel 2001: 118. — Ng et al. 2008: 217 (list).

Type locality. Hawaiian Islands.

Material examined. PERSIAN GULF, Iran: 1 male ( ZUTC Brach1137), under decayed wood, mangroves, Bandar- Khamir, Hormozgan, 26º 28'N, 55º 35'E, coll. R. Naderloo, 29.12.2005; 1 male, 3 juv. ( ZUTC Brach1201), rocky shore, east of Kong Harbour, Hormozgan, coll. R. Naderloo, 02.01.2006; 1 male ( SMF 38444), mangroves, S. coast, Qeshm I., 26º 43'N, 55º 49'E, coll. R. Naderloo & M. Türkay, 09.01.2008; 1 male, 1 female ( SMF 38445), muddy-sand, Tula, Qeshm I., 26º 59'N, 56º 12'E, coll. R. Naderloo & M. Türkay, 13.01.2008. UAE: 1 male ( SMF 97394), sandy-mud, Um Al-Qaiwain, 25º 35'N, 55º 34'E, coll. M. Apel, 09.07.1995; 1 male, 1 female (3 ovig.) ( SMF 973953), mangroves, Khor, Ras Al- Khaymah, 25º 46'N, 55º 58'E, coll. M. Apel, 10.07.1995; 1 male, 2 females ( SMF 97396), rocky intertidal, Abu Dhabi, 24º 55'N, 52º 51'E, coll. M. Apel, 17.07.1995.

GULF OF OMAN, Iran: 1 male, 7 females ( ZUTC Brach1146), mangroves, Khor-Khalasi, Jask, Horzmozgan, 25º 35'N, 58º 02'E, coll. R. Naderloo, 21.11.2005; 2 males, 14 females, 2 juv. ( ZUTC Brach1182), mangroves, Khor-Khalasi, Jask, Hormozgan, 25º 35' N, 58º 02' E, coll. R. Naderloo & A. Kazemi, 21.11.2005; 1 male ( ZUTC Brach1162), mangroves, Khor-Khalasi, Jask, Hormozgan, 25º 35'N, 58º 02'E, coll. R. Naderloo & A. Kazemi, 21.11.2005. UAE: 2 males, 4 females (3 ovig.) ( SMF 37393), mangroves, Fujairah, Khor Kalba, 25º 01'N, 56º 21'E, coll. M. Apel, 0 1.07.1995.

Redescription. Carapace ( Figs. 4 a, 5f) about 1.25 as broad as long, maximum breadth slightly behind exorbital angles, slightly convex; carapace regions poorly defined, lineal depression between gastric and cardiac region; cardiac, intestinal regions faintly defined by depression; lateral region with 10 curved ridges, second, last ones longer than others, short ridges behind frontal lobes. Frontal region with 4 lobes, median 2 slightly smaller than lateral 2, moderately granular on anterior margin; frontal region deflexed downwards, frontal edge about 0.58 times as broad as carapace, slightly longer than posterior edge of carapace. Supraorbital margin smooth, nearly sinuous. Infraorbital margin ( Fig. 4 b) with denticles on medial portion, relatively large, irregular; outer portion oblique, smooth, separated from exorbital angle by deep U-shaped notch; inner angle broadly triangular, with faint ridge on medial part.

Lateral margin without tooth (except of exorbital angle), behind exorbital angle straight, then getting convergent, from medial part getting again divergent, making lateral margin slightly concave ( Fig. 4 a).

Chelipeds subequal. Ischium of large cheliped with 2 sharp teeth on anterior margin, that of small cheliped with 3 or 4 small sharp teeth. Anterior margin of merus with 3 blunt teeth on proximal part, 4 sharp triangular teeth on distal part; posterior surface with smooth transverse ridges. Carpus with spine-shaped tooth distally on inner margin, with small supplementary tubercles around large tooth; posterior surface with transverse ridges, small granules scattered on it. Manus with outer surface ( Fig. 4 c) smooth over most part, with microscopic granules, some oblique ridges on lower proximal portion; longitudinal, finely granular ridges along lower portion; upper margin with large granules; lower margin with small tubercles; inner surface with oblique ridges on proximal part. Fingers smooth, curved inwards distally; small denticles along upper margin of movable finger, smaller distally; cutting edges with moderate gap in proximal half, tubercle-shaped teeth along cutting edges, that of unmovable finger with large tooth on median part ( Fig. 4 c).

Walking legs ( Fig. 4 d), flattened. Merus with anterior margin serrated, with subdistal spine; posterior distal portion with 4 spines, becoming smaller distally; upper surface with transverse ridges, scarce on last legs. Propodus with black bristles along anterior, posterior margins, 2 large spines on posterior distal part. Dactylus with 6 spines along anterior margin, 4 spines along posterior margin, scattered black bristles along anterior, posterior margin.

Male abdomen ( Fig. 4 e) with third somite slightly shorter than fourth; sixth about as long as fifth, with lateral margin nearly straight in three quarters of proximal part, roundly divergent distally; telson long, about 1.5 times as long as sixth somite.

G1 ( Fig. 4 f) relatively stout, in particular in proximal half, sperm canal spiral form, apical chitinous process remarkably long, gently curved outwards; long setae on distal portion, not concealing apical long process.

Female gonopore ( Fig. 4 g) at anterior edge of sternite, nearly semicircular; operculum relatively wide, gently narrowing, apically rounded, located closely at bottom of depression, directed forward.

Remarks. Metopograpsus thukuhar is widely distributed in the Indo-West Pacific and has been well documented by several authors (e.g. Crosnier 1965; Holthuis 1977; Vannini & Valmori 1981; Tirmizi & Ghani 1996). This species is distinguishable from its sympatric conger in the region, M. messor , using several distinct characteristics which are listed in Table 2 .

Biology. Metopograpsus thukuhar is a medium-size species (largest male CL = 19.96 mm, CB = 24.66 mm, largest female CL = 23.25 mm, CB = 29.82 mm) that is typically found among the pneumatophores and tree zones in mangrove forests, where it is sympatric with its congener M. messor . Macrophthalmus thukuhar is not as common as the latter in the Persian Gulf and it is occasionally seen on open muddy ground in seaside fringe of mangroves. It has also been recorded from mangroves in the Red Sea (see Holthuis 1977). Active crabs were mostly recorded out of water during high tide, in particular among the roots immediately above the water level or, rarely, on the trunk of Kenya mangroves ( Fratini et al. 2000). Metopograpsus thukuhar mainly hides in small holes providing by the crossing of the mangrove roots and by the roots entering the mud. It has never been observed digging burrows ( Fratini et al. 2000). This is basically an algivorous crab grazing on the roots and trunk of the mangroves during low tide, but sometimes moving onto open ground to catch smaller crabs such as Uca spp. and Dotilla fenestrata in Kenyan mangroves ecosystem. Fratini et al. (2000) analyzed the content of M. thukuhar midgut in Kenya, showing that about 2.5% of its food items are animals, therefore proposing that it is omnivorous rather than herbivorous.

This medium-size species is present in smaller populations in the Persian Gulf and Gulf of Oman mangal system, in comparison to its sympatric congener M. messor . In Kenya, however, M. thukuhar occurs in relatively large populations together with Perisesarma guttatum . These two species are the two most common crabs of the East Africa mangrove fauna ( Fratini et al. 2000, Vannini et al. 1997, Gillikin & Schubart 2004).

Colour. The colour pattern is similar to that of M. messor . The carapace is slightly darker, with brown spots covered most of the gray background of the carapace. Chelipeds are dark gray to pale orange, with small brown dots. Walking legs are dark gray with brown dots mainly scattered on anterior margin.

Regional records. PERSIAN GULF: UAE ( Al-Ghais & Cooper 1996; Hornby 1997), Iran (present study). GULF OF OMAN: UAE ( Hornby 1997; Apel 2001); Iran (present study).

Geographical distribution. Indo-West Pacific: South Africa, Madagascar, Seychelles, East Africa, Red Sea, Gulf of Aden, Persian Gulf, Gulf of Oman, Pakistan, India, Vietnam, China, Japan, Australia, Tahiti, Hawaii.

Figures

FIGURE 4. Metopograpsus thukuhar (Owen, 1839), male (ZUTC Brach 1162), a – f; female (ZUTC Brach 1162): g. a, posterior surface of carapace; b, lower orbital margin of male; c, cheliped of male, outer surface; d, third walking leg of male (left); e, male abdomen; f, G 1, lateral surface (right); g, female gonopore (right).