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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.

Aplysina cauliformis, the Caribbean purple rope sponge, is commonly affected by Aplysina Red Band Syndrome. This transmissible disease manifests as circular lesions with red margins and results in bare spongin fibers. Leptolyngbya spp. appear to be responsible for the characteristic red coloration but transmission studies with a sponge-derived isolate failed to establish disease, leaving the etiology of ARBS unknown. To investigate the cause of ARBS, contact transmission experiments were performed between healthy and diseased sponges separated by filters with varying pore sizes. Transmission occurred when sponges were separated by filters with pore sizes ≥2.5 μm, suggesting a prokaryotic pathogen(s) but not completely eliminating eukaryotic pathogen(s). Using 16S rRNA gene sequencing methods, thirty-eight prokaryotic taxa were significantly enriched in diseased sponges, including Leptolyngbya, whereas seven taxa were only found in some, but not all, of the ARBS-affected sponges. These results do not implicate a single taxon, but rather a suite of taxa that changed in relative abundance with disease, suggesting a polymicrobial etiology as well as dysbiosis. As a better understanding of dysbiosis is gained, changes in the composition of associated prokaryotic communities may have increasing importance for evaluating and maintaining the health of individuals and imperiled coral reef ecosystems.

Hydroid species (Cnidaria, Hydrozoa) are commonly found as epibionts on organisms within the phyla Porifera, Cnidaria, Bryozoa, Annelida, and Mollusca. A few have also been reported as epibionts of fish, with two reports of associations between hydroids and the family Syngnathidae, which includes pipefishes, sea horses, and seadragons. The hydrozoan Gonothyraea loveni was found on a straightnose pipefish, Nerophis ophidion, in the Gulf of Gdańsk (Baltic Sea; Dziubińska and Sapota 2013), and negatively impacted its ability to swim, while the hydrozoan Hydrichthys mirus produced thin plates on the skin of a Choeroichthys brachysom pipefish from the Bismarck Sea (Papua New Guinea) to parasitize the host (Boero et al. 1991). In both cases, the Syngnathidae hosts died shortly after the observations.In June 2018, hydrozoan zooids were found for the first time colonizing a sea horse (Hippocampus reidi) at a depth of 26 m in the Caribbean Sea (Roatan, Honduras; Fig. 1a, b). Unlike what was observed previously, small hydroids (1-2 mm) were distributed across the surface of the sea horse, which did not appear to be in poor body condition nor have balance issues. However, because the observation was made on the reef, while the fish was attached to an Amphimedon compressa sponge, we have no information on the ultimate fate of the sea horse. Visual analyses of the sea horse-associated hydroids suggest they belong to the family Campanulariidae (Leptothecata, Hydrozoa) and most likely to the genus Clytia. Members of Clytia are poorly described, and further morpho-molecular studies are needed for accurate species-level identification.Hippocampus reidi, one of three species of sea horses inhabiting the Caribbean Sea, utilizes various structures as holdfasts, including sponges, which are known to be suitable substrate for hydroids (Fig. 1c), and may have served as a mechanism for the acquisition and possible subsequent dispersion of hydroids. This sea horse species is classified by the IUCN as 'near-threatened,' and its presence in Roatan waters has declined approximately 30% over the past 10 years, enhancing the importance of this discovery, particularly if the hydroids do not harm their host.