PROCEEDINGS OF THE BIOLOGICAL SOCIETY OF WASHINGTON 1134): 1162-1 172. 2000. Three species of toxic sponges from Cebu, Philippines (Porifera: Demospongiae) G. J. Bakus and G. K. Nishiyama Department of Biological Sciences, University of Southern California, Los Angeles, California 90089-0371 U.S.A. (e-mail: gbakusearthlinknet) Abstract. — Three species of sponges toxic to hard corals are described from Mactan Island, Cebu, Philippines. They were most common at depths of 8-12 m, but they occurred between 3 and 32+ m. Plakortis lita forms thick crusts or is subglobular or massive and liver brown. Birds are very densely packed and irregularly distributed. Tions are rare and microrhabds absent. Acervochalina hooperi, new species, forms thin crusts and is dark green. Thick branching spongin fibers are embedded with small oxeas. Xestospongia vansoesti, new species, forms thick crusts but can be digitate, and dark green to black. Dense multispicular tracts contain foxes. The sponge produces a copious brown mucus. Since 1994 we have been periodically studying the coral reef community and specifically the sponges of Cebu, Central Philippines. Nishiyama (Nishiyama & Bakus 1999) discovered that all three species of sponges described below were releasing allomones into the surrounding seawater. These allomones were toxic to some hard corals which suggests that the sponges and hard corals are competing for space. Thus, sponge toxins may play an important role in the structuring of coral reef communities. We are herein describing these species of sponges from our ecological field studies. Materials and Methods Site description. — Our study site is located approximately 200 m off the Tubuli Beach Resort on the east coast of Mactan Island near Cebu City (1017N, 124E) (Fig. 1) (Bakus and Nishiyama 1999). Depths surveyed were 3-32 m. The area has a narrow intertidal region followed by seagrasses (principally Thalassia hemprichii) to a depth of 5-10 m, then a rich coral reef community to a depth of at least 40 m, with the slope becoming steeper beyond a depth of 20 m. The dominant hard corals in the region include Acropora, Pocillopora, Seriatopora, Tubipora, Halomitra, Parahalomitra, Lobophyllia, Symphyllia, Euphyllia, Pectinia, Porites, Montipora, Millepora and Fungia (University of San Carlos Marine Biology section 1979). The average current velocity at the study site was 009 sec although flow rates as high as about 39 sec (2 knots) occur occasionally during shifting tides. Current direction during our June-july studies was from 60° NE or 220-240° SW, depending on the tides. The water temperature was 28-3 1C although it can get as low as 26C in February (F. Sotto, pers. comm). Underwater visibility was 15-30 m. The three species of sponges occurred at depths of 3-32+ m. They were most common at depths of 812 m. Sponges were collected in the field by hand, frozen in a — 30C freezer, and studied later in the laboratory. Scanning electron micrographs (SEM) of spicules were made with a Cambridge 360 SEM. Spicules were measured with a Zeiss Compound Microscope fitted with an ocular micrometer. Sponge skeletons were digitized with a RCA TC 1005 camera connected to a Data Translation 3155 frame grabber board in a