ON SOME CRUSTACEAN ASSOCIATES OF ECHINODERMATA FROM THE BAY OF BENGAL

Associations in marine environment are common· It is particularly 10 with echinoderms, for the arms and pinnules of crinoids, the ambulacral grooves and spinous armature of asteroids and ophiuroids, the thick forest of spines and pedicellariae of echinoids and the cloaca of holothurians serve as attractive habitats for a variety of symbionts ranging from Protozoa to Pisces. The associates and their adaptations to the special biotope and relationships with their hosts and other members of the community, have been dealt with in detail by many, especially Hyman (1955), Dales (1957, 1966), Hopkins (1957), Davenport (1966) Fischelson (1973) and Bruce (1976). There are several reports on the crustacean associates of Indian Echinodermata, notably those of Kemp (1922), Chopra (1931), Jones and Sankarankutty (1960), Jones and Mahadevan (1965), Reddiah (1966, 1968), Rao and Sowbhagvavathi (1912) Ganapati and Sastry (1972) and Daniel and Krishnan (1978). During the recent survey to Andaman and Nicobar Islands, led by Shri O. Ramakrishna (Superintending Zoologist), two species of "shrimps accociated with sea-urchins were collected by the author, a preliminary report of which has already been made (Sastry, 1977). An examination of the unnamed National Zoological Collections, revealed some more decapod crustacean associates of echinoids and crinoids which are being reported here. The following is the list of crustacean associates dealt with in the present communication.

During the recent survey to Andaman and Nicobar Islands, led by Shri O. Ramakrishna (Superintending Zoologist), two species of "shrimps accociated with sea-urchins were collected by the author, a preliminary report of which has already been made (Sastry, 1977).
An examination of the unnamed National Zoological Collections, revealed some more decapod crustacean associates of echinoids and crinoids which are being reported here.The following is the list of crustacean associates dealt with in the present communication.Remarks: The shrimps were dark pink in colour appearing almost black when alive.Body robust, with heavy chelae.Rostrum lanceolate with margins parallel near the base and converging distally to a blunt tip, reaching a little beyond the middle of the second antennulal' article.Carpus of the second legs four segmented.Merus of third legs with a notch on the outer distal margin and dactylus biunguiculate.
AD the four females are carrying eggs on the abdomen and bave the ~ maBculifttJ on the second pleopods, as long as the appen,di2; itaIertIa.In males the al'pendi:r: maBculina is longer than the appendix itIIerM and bears longer spines (Text-figs.On a comparison with the present material, it appears that the ahrimps associated with Stomopneustes variolaris on the Visakhapatnam Coast (Ganapati and Sastry, 1972) are also A. dorsalis.The present material also was collected from the same sea-urchin and in a similar habitat. •22

Records of tke ZooZogicaZ Survey oj IflAlia
Distribution: Indo-west Pacific.From peninsular India it was reported in the Gulf of Mannar (Sankarankutty, 1962) and along the Visakhapatnam Coast (Ganapati and Sastry, 1972).
The species is recorded here for the first time from the Andaman and Nicobar Islands.
2. Athanas indicDs    Remarks: The specimens were reddish brown with one median and two lateral yellowish longitudinal stripes on the dorsal side.Body smooth and slender.Rostrum triangular, tip pointed, reaching from the middle of the second article to the tip of the antennular peduncle.Carpus of second legs four segmented.Outer inferior distal margin of merus of third legs produced into a tooth-like projection and dactylus biunguicula tee All the eleven females are carrying eggs on the abdomen and eight of them have a diminutive appendix masculina of about one third the length of append1:x interna on the second pleopods.In nine males the appendix masculina is a little shorter than the appendix interna while in the tenth it slightly exceeds the appendix interna.(Text-figs.

D, E).
The shrimps were collected from Echinometra mathaei inhabiting the bores made by the urchin in hard clay mounds and corals.Remarks: In the specimen from Peel Island, the rostrum reaches to about two thirds of the second article of the antennular peduncle and the propodus of the third pereiopod bears 16 spines.In the one from Havelock Island the rostrum reaches beyond the middle of the .third article of the antennular peduncle and the propodus of the third pereiopod bears only 10 spines.Though Banner and Banner (1966) characterised li.stimpsonii as having more than 10 spines (figure shows 16 spines), they however found later (1968,1975) the number to vary from 6-10 in their Australian specimens.They also observed the rostrum to reach from distal quarter of the first to beyond the end of the second antennular article.The shrimps were associated with crinoids and are black in colour as the preserved crinoids.
Distribution: Bay of Bengal and from Singapore and Japan to Marshall Island Gilbert Is. and Australia.George et al (1973)     placed behind the orbit and three on the lower side.The carapace bears strong supra corneal, antennal and hepatic spines.The fingers of first chelae have fine teeth arranged like a comb.Unfortunately both the second chelae are lost in the present specimen.However, in all other characters, the specimen agrees with the figures of p. 8piniferu8 given by Borradaile (1917) and the specimens of the same species in the Indian Museum, reported by Kemp (1922).Moreover, it differs from the other species of the subgenus with denticulated first chelae, in having the supra orbital spine.
This ,species was usually reported from corals.The present specimen is from a crinoid.
Distribution: Indo-west Pacific from Madagascar to S. Pacific Is.The species is here recorded for the first time from Mergui Archipelago.Remarks: Carapace sharply pentagonal with the anterolateral margins produced into a rostrum.Upper surface pink with two parallel white stripes in the posterior half of the carapace and the rostrum with a white margin.
The specimen is a female carrying eggs.It was found in the rectum of the sea-urchin EchinothTix diadema (Linnaeus).Due to the presence of the crab, the apical system of the sea-urchin was distorted.
Distribution: Indo-west Pacific.The species is recorded here for the first time from Indian coast.

DISCUSSION
The study of animal associates is important because of thei adaptations to the special biotope and their relationship with the host and other members of the community.Though the echinoderm hosts are provided with varied defensive mechanisms such as mucous secretions, spines, pedicellariae, cuverian tubules etc. the symbionts seem to have adapted themselves to the protective devices of the echinoderms and made them a congenial habitat.In most cases the symbiont gets its protection and food associated with the host.They also make their presence inconspicuous by means of concealing colouration.Thus the colourations of Athanas dorsalis, A. indicus, and Echinoecus pentagonus closely approach those of their respective hosts.The stripes of A. indicus and E. pentagonus distort the outline of the body.The colouration of Synalpheus stimpsonii is not known in the present material.The pontoniid species is in general transparent while alive, and thus suits to any back ground.Ganapati and Sastry (1972) observed that A. dorsalis actively searches for its host when dislodged from the latter and finds its host by photoreception.It is protected from enemies because of concealing colouration and from environmental stresses of temperature, desiccation etc. because of its occurrence among the tube feet, on the oral side.
It is observed at Camorta Island that A. indicU8 also behaves in a similar way.Thus both the species appear to be obligate commensals on the Indian coast .
• It was earlier reported that A. dorsalis may not occur in male female pairs (Ganapati and Sastry, 1972).However, further observations on this species at Visakhapatnam and Camorta and on A. indicus at Andaman and Nicobar Islands revealed that both the species do occur in heterosexual pairs and occasionally along with 1 or 2 juveniles.Though these two species have so far been reported from different seaurchins (Banner and Banner, 1960;Miya & Miyake, 1968;Sankarankutty, 1962), the present material indicates a definite host-specificity when occurring sympatrically.Thus all the specimens from Stomopneustes variolaris are A. dorsalis while the ones from Echinometra mathaei are ~.indicus, though the two sea-urchins are from the same locality and •habitat at Camorta Island.
From the reports of Miyake (1939) and Sakai (1956) it appears that the males ~~nd females of the parthenopid crab Echinoecus pentagonus swim freely in the vicinity of various sea urchins and only the females after mating enter the rectum of their hosts.The recent studies of Castro (1971) on the association of this crab with the sea-urchin Eckinothrix calamaris in Hawaii, showed that the males and juvenile females live on the oral side of the host and meet their energy requirements by ingesting epithelial tissue and the tube feet from the peristomial region while the adult females live in the rectum and subsist on the abundant aggregations of coelomocytes and faecal penets of the host.Due to complete metabolic dependency of the .crabon its host, Castro (1971), based on the scheme of Cheng (1967), categorized the association as parasitism.
The author is grateful to the Director, Zoological Survey of India and Shri G. Ramakrishna for the facilities and opportunity to visit .~eAndamanandNicobarIslands.Thanks are also due to Dr. T. n. and Dr. O. C. Rao for encouragement and Mrs. D. M. Banner for .criticallygoingthrough the manuscript.Stimpson, p,.oc • .Acad.Nat.Sci.Philad., 12 : 32.1960.Athanas dorsalis:Banner and Banner, Paciflc Sci., 14 : 151.