The echinoderms of Aldabra and their habitats

The echinoderms of Aldabra and their habitats N. A. Sloan Department of Zoology & Comparative Physiology, Queen Mary College, University of London, Mile End Road, London El 4NS. Interim address: Bermuda Biological Station for Research, St George's West 1-15, Bermuda Ailsa M. Clark & J. D. Taylor Department of Zoology, British Museum (Natural History), Cromwell Road, London SW7 5BD Contents Synopsis ............. 81 Introduction ............ 81 Shallow water habitats of Aldabra ......... 82 Seaward habitats 83 Lagoon and Channel habitats ......... 83 Comparison between the echinoderm faunas of exposed and sheltered rocky shores 84 Exposed rocky shore near Point Hodoul (407-080) ..... 84 Sheltered rocky shore on He Picard (056-100) 85 Ophiocomid microhabitats on Aldabra ........ 89 Associates of Ophiocoma species ........ 93 Systematic account ........... 93 Class Crinoidea ........... 95 Subclass Asteroidea .......... 95 Subclass Ophiuroidea .......... 99 Class Echinoidea . . . . . . . . . . . 117 Class Holothurioidea . . . . . . . . . . 121 Acknowledgements ........... 125 References ............. 125 Synopsis This first full account of the echinoderm fauna of Aldabra Atoll, western Indian Ocean, includes a des-cription of the shallow-water habitats and two special ecological studies dealing with the microhabitats of the Ophiocomidae -the dominant family of coral-reef ophiuroids -and a comparison between the echinoderms of an exposed and a sheltered part of the shore. The remainder consists of an annotated fauna list, with details of habitats, colours in life, parasites, commensals and other observations on the individual species. It is based primarily on recent collections and observations by Sloan, but also takes account of previous work by others at the Royal Society's base on the atoll. Nearly 130 species are included, of which 20% are recorded for the first time from the islands of the western Indian Ocean (excluding the Mascarene Islands). Introduction Aldabra Atoll is a slightly elevated group of four main limestone islands which form a seaward rim with a maximum dimension of 34 km from east to west (see Fig. 1). It lies at 924' S and 4620' E, some 650 km off the African mainland. With the exception of Assumption and Cosmo-ledo, Aldabra is isolated from all land by an oceanic basin. Its east and south seaward shores are the most exposed, being directly in the path of the SE trades, which blow constantly from April to November. During the other months more variable winds blow from the northwest. Detailed Bull. Br. Mus. Nat. Hist. (Zool.) 37 (2) : 81-128 Issued 20 December 1979 81

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