The evolution of symbiotic relationships involving reef corals has had much impact on tropical marine biodiversity. Because of their endosymbiotic algae (zooxanthellae) corals can grow fast in tropical shallow seas where they form reefs that supply food, substrate and shelter for other organisms. Many coral symbionts are host-specific, depending on particular coral species for their existence. Some of these animals have become popular objects for underwater photographers and aquarists, whereas others are hardly noticed or considered pests. Loss of a single coral host species also leads to the disappearance of some of its associated fauna. In the present study we show which mushroom corals (Scleractinia: Fungiidae) are known to act as hosts for other organisms, such as acoel flatworms, copepods, barnacles, gall crabs, pontoniine shrimps, mytilid bivalves, epitoniid snails, coralliophilid snails, fish and certain types of zooxanthellae. Several of these associated organisms appear to be host-specific whereas other species are generalists and not even necessarily restricted to fungiid hosts.Heliofungia actiniformisis one of the most hospitable coral species known with a recorded associated fauna consisting of at least 23 species. The availability of a phylogeny reconstruction of the Fungiidae enables comparisons of closely related species of mushroom corals regarding their associated fauna. Application of a phylogenetic ecological analysis indicates that the presence or absence of associated organisms is evolutionarily derived or habitat-induced. Some associations appear to be restricted to certain evolutionary lineages within the Fungiidae, whereas the absence of associated species may be determined by ecomorphological traits of the host corals, such as coral dimensions (coral diameter and thickness) and polyp shape (tentacle size).

Coral-associated invertebrates dominate the biodiversity of coral reefs. Some of the associations involving symbiotic invertebrates remain unknown or little studied. This holds true even for relatively wellstudied coral reefs, like those in the Caribbean Sea. Coral gall crabs (Cryptochiridae), obligate symbionts of stony corals, form a much-overlooked component of coral reef communities. Most recent studies on the Atlantic members of Cryptochiridae have been conducted off Brazil and little recent data have become available from the Caribbean region. During fieldwork off Curaçao (southern Caribbean Sea), eight new host coral species, belonging to four coral families, were recorded for three cryptochirid species. Kroppcarcinus siderastreicola Badaro, Neves, Castro and Johnsson, 2012, previously only known from Brazil, and Opecarcinus hypostegus (Shaw and Hopkins, 1977) are new additions to the fauna of Curaçao. Besides the new hosts and geographic range extensions, a free-living male Troglocarcinus corallicola Verrill, 1908 was observed visiting a female of the same species lodged in her gall in an Orbicella annularis (Ellis and Solander, 1786) colony. This is the first photodocumented record of the "visiting" mating system in Cryptochiridae