GRAPSID AND XANTHID CRABS OF PARANGIPETTAI COAST

Studies pertaining to the infauna of Parangipettai waters have been in progress since the inception of the Marine Biological Station in the year 1956. With the growth of this station as an Advanced Centre in Marine Research, a more extensive knowledge on the local fauna has become imperative. Special emphasis was. given to this aspect, so as to get a comprehensive idea of community structure and population dynamics of this area. Brachyuran crabs, the most interesting group of organisms among the decapod crustaceans occur in large numbers in the Vellar estuary, Pitchavaram mangroves and in the trawl catches of local mechanised vessels. Sethuramalingam (1983) studied the portunid crabs of Porto Novo coast. No information is yet available regarding the species composition of grapsid and xanthid crabs. In the present study an inventory was made on species composition of the above groups and the results are given here. The terminology used in the keys conform to those of earlier works. The synonyms given are not to be complete.


INTRODUCTION
Studies pertaining to the infauna of Parangipettai waters have been in progress since the inception of the Marine Biological Station in the year 1956. With the growth of this station as an Advanced Centre in Marine Research, a more extensive knowledge on the local fauna has become imperative. Special emphasis was. given to this aspect, so as to get a comprehensive idea of community structure and population dynamics of this area. Brachyuran crabs, the most interesting group of organisms among the decapod crustaceans occur in large numbers in the Vellar estuary, Pitchavaram mangroves and in the trawl catches of local mechanised vessels. Sethuramalingam (1983) studied the portunid crabs of Porto Novo coast. No information is yet available regarding the species composition of grapsid and xanthid crabs. In the present study an inventory was made on species composition of the above groups and the results are given here. The terminology used in the keys conform to those of earlier works. The synonyms given are not to be complete. Last legs not dorsally placed; a gap between third maxillipeds; anterolateral side of carapace striaght or arched; front broad; rarely true land crabs (Fig. 1).
T.iig.2 T,.  Material: 10 males and 20 females ranging from 30 mm to 34 mm in carapace width were collected from Yeller estuary.
In and around India, the occurrence of this species has been reported from Andaman Nicobars, Mergui, Sri Lanka, East and West coasts of India, Sind and Baluchistan.
Remarks: This species is smaller than G. tenuicfustatus and is always found along with the latter. The presence of the straight spine at the inner angle of carpus of cheliped is very much helpful in distinguishing this species from G. tenuicru8tatu8.
Oolour: Carapace velvet green with regularly arranged white patches, concentrated more on epibranchial region along striae; dactylus of pereopods light brown and merus with irregularly scattered white patches which is absent in chela and palm of which appears violet in colour.
Habitat: This species occurs in the constricted rocks, stones and boulders of of railwa y bridge and jetty at Parangipettai and in the oyster bed also.
Distribution: All tropical and subtropical seas.
Remarks: This fairly large sized crab runs faster when approached. It has already been recorded from the rocky habitat. Now it is found to inhabit the oyster bed also.

M. me880r
Material: 10 males measuring carapace width of 21 mm to 26 mm were collected from Pitchavaram mangroves.
Oolour: Carapace dark green, few scattered light green patches on pereopods, dactylus of chelate leg violet.
Habitat: It is found in the muddy substrates of the intertidal region in Pitchavaram mangroves.
Distribution: Along the coasts of India, Ceylon, Mergui and East Indies. It bas been recorded from Bombay coast by Alcock (1900 M ateriaZ: 50 specimens of both m ales and females were collected from Vellar estuary and Pitchavaram mangroves.
Oolour: Carapace dark green with scattered white patches on epibranchial and cardiac regions; pereopods striped with light and dark green bands and dactylus of chela appears bright violet.
Habitat: Abundantly found in rocks and exposed oyster beds in subtidal region and also found in muddy substrata.
Distribution: Ranging from Red sea to Australia.
Remarks: This species is easily distinguishable from M. maculatu8 by the colour pattern and by the triangular shaped last segment of abdomen of male. Distribution: Indo-Pacific. It has been reported from Bombay coast by Chhapgar (1957).
T. Fig.16 T. Fig.17 T 2. Antennal peduncle not excluded from orbit; posterolateral border of merus of pereopods 4-5, without dents (Fig. 16) ; carapace with one or two anterolateral teeth, anterior frontal margin with strong median concavity (Fig. 17) ; upper surface of palm of cheliped with only one of pectinated crest, anterior border of merus of cheliped with sub distal trinangular process distally denticulated (Fig. 18) Neoepisesarma 3. Antennal peduncle not excluded from orbit; posterodistal border of pereopod without denticulation; upper edge of palm of cheliped with 2-3 pectinated crest (Fig. 19)   The subgenus Nanosesarma is represented by a single species and subgenus Beanium by two species in Parangipettai waters.
Oolour: Carapace lemon yellow, cardiac region less brighter; pereopod, with 'yellow and light green bands, chela bright yellow.
Habitat: Occurs in the muddy substrata along intertidal area and also in loosely packed oyster shells in the subtidal area. Material: 100 males and 100 females were collected from Pitchavaram mallgroves and Vellar estuary.

Records of the Zoological Survey oj India
Oolour: Carapace light green in general, mesogastric and cardiac regions bright coloured; pereopods with less pronounced stripes and dactylus of cheliped with light brown colour.
Habitat: Inhabits the oyster bed in the intertidal region of Vellar estuary and Pitcbavaram mangroves.
Distribution: Widely distributed in Indo-Pacific region.
Remarks: This small grapsid crab dominates the crab fauna of oyster bed community. More Dumber of adult specimens were collected during summer whereas during monsoon season, the juveniles were mote. (i) Longitudinal dactylar tubercles widely separated from one another, a clear sulcus running between them, vertical granular crest on inner palm of cheliped strongly salient (Fig. 30 Material: 3 males and 3 females were collected from Pitchavaram mangroves.
Habitat: Inhabits burrows as deep as one meter in the muddy substratum along intertidal area of Pitchavaram mangroves.
Remarks: This is recorded for the first time in Parangipettai coast. Altogether 3 males and 3 females were collected from the same spot during the study period. It has been observed that this species occurs in limited numbers and restricted to a particular habitat where another species of this genus (tetragonum) is dominant. },f ateriaZ: 100 males and 100 females were collected from burrows found in the muddy substrata of Pitchavaram mangroves and Vellar estuary.
Habitat: Inhabits burrows as deep as 1 meter in muddy and bushy areas of Pitchavaram mangroves along intertidal region.

Di8tribution: Widely distributed in Indo-West Pacific region.
Remarks: In the present study, the generic and subgeneric characters reveal that there are differences in the pectinated crest. Material: 10 males were collected from the tidal zone of the Vellar estuary.
Oolour: Carapace reddish brown, few scattered red spots on epibranchial region, anterolateral teeth on carapace dark red, very light brown band like colouration in merus of pereopods.
Carapace moderately broad, front about a third of greatest breadth of carapace, anterolateral borders of carapace not longer than posterolaterals; basal antennal joint does not or just touches front Pilumninae T. Fig.36 . ,- Key to genera and 8pecies of X anthinae 1. Carapace perfectly smooth, no trace of regions, anterolateral border entire Liagore Front faintly bilobed; little pimple like thickenings (tubercles) on outer angle of orbit; borders of merus hairy, upper borders with a denticle, dactyli of leg elongately plumed; reddish spots on carapace (Fig. 38) as well as on legs u.

L. rubromaculatU8
Records of the Zoological Survey oJ 1 ndia 3. Anterolateral borders of carapace lobed, first two indistinct, carapace regions and subregions well defined (Fig. 40  Remarks: In Parangipettai region this species is being eaten by coastal inhabitants. This species dominates the catches during summer months. The systematic position of bispinosa is still uncertain. Though the adults have all the morphological characteristics of the subfamily Xanthinae, the larvae (Mohan, 1984) showed close similarities to piluminids in their antennal morphology (Hyman, 1925) and armature of abdominal segments (Sandifer, 1974). As revealed by larval characteristics this species should be removed from Xanthinae and included into the subfamily Pilumninae.