A comprehensive inventory of global biodiversity would be greatly improved by automating methods for species delimitation. The Automatic Barcode Gap Discovery method, the Poisson tree processes algorithm and the Generalized mixed Yule-coalescent model have been proposed as means of increasing the rate of biodiversity description using single locus data. We applied these methods to explore the diversity within the Aglaopheniidae, a hydrozoan family with many species widely distributed across tropical and temperate oceans. Our analyses revealed widespread cryptic diversity in this family, almost half of the morpho-species presenting several independent evolutionary lineages, as well as support for cases of synonymy. For two common species of this family, Lytocarpia brevirostris and Macrorhynchia phoenicea, we compared the outputs to clustering analyses based on microsatellite data and to nuclear gene phylogenies. For L. brevirostris, microsatellite data were congruent with results of the species delimitation methods, revealing the existence of two cryptic species with Indo-Pacific distribution. For M. phoenicea, all analyses confirmed the presence of two cryptic species within the South-Western Indian Ocean. Our study suggests that the diversity of Aglaopheniidae might be much higher than assumed, likely related to low dispersal capacities. Sequence-based species delimitation methods seem highly valuable to reveal cryptic diversity in hydrozoans; their application in an integrative framework will be very useful in describing the phyletic diversity of these organisms.

Three species of fire corals are present on the fringing coral reefs of Reunion Island (SW Indian Ocean): Millepora exaesa, Millepora platyphylla and Millepora tenera. Compared with scleractinian corals, reproduction studies on milleporids are scarce and this is the first study to be conducted in the Indian Ocean and on M. exaesa. We used a combination of weekly in situ observations and laboratory studies to document reproductive stages and phenology. The sexual reproductive period was the austral summer (Nov–Jan), the maturation of the colonies being correlated to the seasonal increasing water temperature. We describe both ampullae and short‐lived medusae (medusoids), and report differences in the size and density of ampullae and the distribution of nematocysts in the medusoids of the three species. The absence of radial and circular canals in all medusoids agrees with the original description but not with the current diagnosis of the family Milleporidae. We observed the first mass spawning event in M. exaesa and M. platyphylla, and provide the first description of a zooxanthellate Millepora larva. Spawning always began before dark but was not correlated with the lunar or tidal cycles. Millepora tenera colonies released several batches of medusoids during the reproductive period, suggesting that this species may be a serial spawner.

Coral microbiomes are critical to holobiont functioning, but much remains to be understood about how prevailing environment and host genotype affect microbial communities in ecosystems. Resembling human identical twin studies, we examined bacterial community differences of naturally occurring fire coral clones within and between contrasting reef habitats to assess the relative contribution of host genotype and environment to microbiome structure. Bacterial community composition of coral clones differed between reef habitats, highlighting the contribution of the environment. Similarly, but to a lesser extent, microbiomes varied across different genotypes in identical habitats, denoting the influence of host genotype. Predictions of genomic function based on taxonomic profiles suggest that environmentally determined taxa supported a functional restructuring of the microbial metabolic network. In contrast, bacteria determined by host genotype seemed to be functionally redundant. Our study suggests microbiome flexibility as a mechanism of environmental adaptation with association of different bacterial taxa partially dependent on host genotype.