Marine hydroids are important benthic components of shallow and deep waters worldwide, but their taxonomy is controversial because diagnostic morphological characters to categorize taxa are limited. Their genetic relationships are also little investigated. We tested taxonomic hypotheses within the highly speciose superfamily Plumularioidea by integrating a classical morphological approach with DNA barcoding of the 16S and COI mitochondrial markers for 659 and 196 specimens of Plumularioidea, respectively. Adding Genbank sequences, we inferred systematic relationships among 1,114 plumularioids, corresponding to 123 nominal species and 17 novel morphospecies in five families of Plumularioidea. We found considerable inconsistencies in the systematics of nominal families, genera and species. The families Kirchenpaueriidae and Plumulariidae were polyphyletic and the Halopterididae paraphyletic. Most genera of Plumularioidea are not monophyletic. Species diversity is considerably underestimated. Within our study, at least 10% of the morphologically-distinctive morphospecies are undescribed, and about 40% of the overall species richness is represented by cryptic species. Convergent evolution and morphological plasticity therefore blur systematic relationships. Additionally, cryptic taxa occur frequently in sympatry or parapatry, complicating correspondence with type material of described species. Sometimes conspecificity of different morphotypes was found. The taxonomy of hydroids requires continued comprehensive revision.

The hydrozoan family Aglaopheniidae (Cnidaria) is widespread worldwide and contains some of the most easily recognizable hydroids because of their la

Organic falls create localised patches of organic enrichment and disturbance where enhanced degradation is mediated by diversified microbial assemblages and specialized fauna. The view of organic falls as “stepping stones” for the colonization of deep-sea reducing environments has been often loosely used, but much remains to be proven concerning their capability to bridge dispersal among such environments. Aiming the clarification of this issue, we used an experimental approach to answer the following questions: Are relatively small organic falls in the deep sea capable of sustaining taxonomically and trophically diverse assemblages over demographically relevant temporal scales? Are there important depth- or site-related sources of variability for the composition and structure of these assemblages? Is the proximity of other reducing environments influential for their colonization? We analysed the taxonomical and trophic diversity patterns and partitioning (α- and β-diversity) of the macrofaunal assemblages recruited in small colonization devices with organic and inorganic substrata after 1-2 years of deployment on mud volcanoes of the Gulf of Cádiz. Our results show that small organic falls can sustain highly diverse and trophically coherent assemblages for time periods allowing growth to reproductive maturity, and successive generations of dominant species. The composition and structure of the assemblages showed variability consistent with their biogeographic and bathymetric contexts. However, the proximity of cold seeps had limited influence on the similarity between the assemblages of these two habitats and organic falls sustained a distinctive fauna with dominant substrate-specific taxa. We conclude that it is unlikely that small organic falls may regularly ensure population connectivity among cold seeps and vents. They may be a recurrent source of evolutionary candidates for the colonization of such ecosystems. However, there may be a critical size of organic fall to create the necessary intense and persistent reducing conditions for sustaining typical chemosymbiotic vent and seep organisms.

Moon jellies are some of the most popular, widely distributed, and best-studied marine jellyfish. By the end of the past century only two or three Aurelia species were recognized, but with the rise of DNA barcoding studies, around thirty Aurelia species are presently accepted. Most of the species are morphologically indistinguishable and have restricted biogeography. We reveal, with COI, 16S, and ITS1-5.8S sequence data, two (pseudo-)cryptic species of Aurelia, potentially endemic to the Azores ecoregion, herein provisionally classified as A. “cf. pseudosolida” and A. “misteriosa”. These species are closely related to the Mediterranean lineages of A. pseudosolida and A. persea, respectively. In the Azores, the shape of the campanula and oral arms readily distinguishes the two species: the former with folded oral arms and globose campanula, and the latter with flattened campanula and thick and long oral arms. Previous reports of A. solida and A. aurita in the Azores should generally correspond to A. “misteriosa” and A. cf. pseudosolida, respectively. The phylogenetic (re-)examination of the available DNA barcodes of Aurelia only evidenced human-mediated dispersal for A. coerulea, A. relicta, and A. aurita. Aurelia solida cannot be yet considered NIS in the Mediterranean. More jellyfish DNA (meta)barcoding should reveal further cryptic diversity, biological invasions, and phylogeographic inferences.