/. Mar. Biol. Ass. U.K. (1998), 78, 59-73 59 Printed in Great Britain ALECTONA SPECIES FROM NORTH-WESTERN PACIFIC (DEMOSPONGIAE: CLIONIDAE) GIORGIO BAVESTRELLO, BARBARA CALCINAI, CARLO CERRANO AND MICHELE SARA Istituto di Zoologia dell'Universita di Genova, Via Balbi 5-16126 Genova, Italy Alectona species which bore into the scleraxis of several colonies of Corallium elatius and the stem of a stylasterid coral, Distichopora sp. have been studied. The genus Alectona consists of rarely collected species. Five species, of the eight known for the genus, are here recorded. Two new species of Alectona sorrentini and A. microspiculata and one uncertain species are described. In recent reefs Cliona species are the predominant boring sponges while Alectona and Thoosa were common in the Eocene/Miocene coral reefs. The deep precious red coral communities of the western Pacific may be interpreted as refuge habitats of these ancient boring sponges. INTRODUCTION The genus Alectona was erected by Carter (1879) for A. millari from the North Atlantic collected at 664 m depth. In the same paper, the author considers Gummina wallichii (Carter, 1874), from Agulhas Shoal, as a variety of Alectona millari and includes G. wallichii in the genus Alectona. The following year, Carter (1880) added the new species A. higgini, subsequently assigned by Laubenfels (1936) to the genus Delectona. In the definition of the genus, Carter based his diagnosis on ". . . spicule acerate, abruptly curved or bent in the centre, tubercled throughout. Flesh-spicules spindle-like, consisting of a straight shaft, pointed at the extremities and encircled by two rings of tubercles equidistant from each other and from the ends of the shaft respectively". Other species were described by Johnson (1899), Topsent (1932), Pang (1979) and Levi & Levi (1983); up to a total number of six species of Alectona: A. wallichii, A. millari, A. verticillata, A. primitiva, A. jamaicensis and A. triradiata. The distribution of these species is generally circumtropical even if A. millari is described from North Atlantic and Mediterranean, and A. verticillata is a record from Madeira. The distribution is probably related to the particular affinity of these boring sponges for organogenous substrata such as madreporian corals. Only A. millari and, probably, A. triradiata are able to excavate inorganic limestone. In this work we describe five species of Alectona two of which are already known, A. wallichi and A. triradiata; two new, A. sorrentini and A microspiculata, and one uncertain. The species examined were included in the large scleraxis of Corallium elatius from a commercial stock of the Japan Sea, collected by commercial fisheries and