The phylum Entoprocta is one of the most enigmatic groups of living invertebrates, although approximately 200 species are currently recognized (Nielsen 2013). Entoprocts are suspension feeders distributed worldwide, and most species live epizooically on other marine organisms (Iseto 2010). The only association recorded from the Indian Ocean is represented by three species belonging to the genus Loxosoma, associated with tube-building polychaetes found in Thailand (Nielsen 1996). During a recent biodiversity survey on Kunfunadhoo Island, Baa Atoll, Maldives (05°07′N, 73°04′E), entoproct zooids were found in association with four genera of sponges—Cliona, Clathria, Dragmacidon and Petrosia—at depths of 5–32 m (Fig. 1a, b). Morphological analyses of all sponge-associated entoprocts revealed the presence of a foot-like appendage with a foot gland (fg) and groove (gr) at the base of the stalk (Fig. 1c), which are two distinctive features of the solitary genus Loxosomella (Iseto 2010). To the best of our knowledge, this is the first record of an association between Loxosomella and sponges in the Indian Ocean, as well as the first discovery of the phylum Entoprocta in the Maldivian archipelago. Organisms such as entoprocts are often overlooked in the field because of their small size (0.2–5 mm). Therefore, we strongly recommend additional ecological investigations of interspecific interactions involving tropical entoprocts and morpho-molecular studies targeted to detect the real diversity of this phylum. Our findings confirm that coral reef-associated biodiversity and the potential benefits and disadvantages of interspecific interactions remain insufficiently explored in the Indian Ocean.

Fig. 1
figure 1

a Clathria sp. colonized by many entoproct zooids. b High magnification of Petrosia sp. showing individual entoproct zooids extending their tentacles. c Specimen of Loxosomella sp. found in association with Clathria sp. fg foot gland, gr foot groove

Full size image