Fauna associated with the horny sponge Anomoianthella lamella Pulitzer-Finali & Pronzato, 1999 (Ianthellidae, Demospongiae) from Papua-New Guinea

The relationships between the tropical sponge Anomoianthella lamella Pulitz er-Finali & Pronzato, 1999 (from Papua-New Guinea) and its endobionts, the barnacle Acasta sp. and the polychaete Haplosyllis spongicola (Grube, 1855) , were analysed using optical and scanning electron microscope techniques. The specimens of Acasta sp. live in the mesohyl, close to the inhalant surf ace of the sponge, where they reach a mean density of 12.7.10 cm(-2). Their apical region is delimited by a thin layer of sponge collagen, whereas spo nge cells (archeocytes and lophocytes) gather along the rest of the body of the endobiont. While the barnacles adhere to the spongin skeleton network, the polychaetes H. spongicola are esclusive to the exhalant canals of the sponge aquiferous system, where they reach a mean density of 57 individuals .cm(-2). No evidence of sponge reaction to H. spongicola was observed. Pote ntial benefits for the barnacle are protection, against predation and mecha nical disturbance, and trophic advantages. Conversely, the barnacle may con tribute to strengthen the sponge skeletal network. The association with pol ychaetes can be regarded as a simple commensalism-parasitism relationship.