Description: We used carbon and nitrogen stable isotope (δ13C and δ15N) analyses to investigate the trophic network of the CWC reef habitat off Angola (SE Atlantic Ocean). Samples were collected in January 2016 during the M122 (“ANNA”) expedition on board R/V Meteor. In total, 18 reef sites, including seven CWC mound settings over a bathymetric range of 250 to 530 m water depth, were sampled for stable isotope analyses. Samples of organisms belonging to the taxa Porifera, Cnidaria, Arthropoda, Annelida, Echinodermata and Chordata were collected by means of a box corer, a Van-Veen grab sampler and the Remotely Operated Vehicle (ROV) SQUID (MARUM, Bremen, Germany). To investigate potential food sources of the benthic megafauna, three types of Particulate Organic Matter (POM) were collected: Suspended Particulate Organic Matter (SPOM) was collected with a McLane phytoplankton pump; settling SPOM was collected with a sediment trap (SPOM trap) and sediment samples were collected with a box corer and a grab sampler. Analyses of benthic megafauna were performed using a Elementar IsoPrime 100 isotope ratio–mass spectrometry (IR–MS) (IsoPrime Ltd.) coupled to a CNS elemental analyzer (Elementar Vario Pyro Cube EA CNS; Elementar Analysensysteme GmbH), while POM samples were analyzed by a Delta V Advantage IR–MS coupled online to an elemental analyzer (Flash 2000 EA-IRMS) by a ConFlo IV (Thermo Fisher Scientific Inc.). Vienna Pee Dee belemnite (V.P.D.B.) for carbon, and atmospheric N2 (Air) for nitrogen, were used as reference materials, and stable isotope values are reported in respect to that.

Description: Capitate hydrozoans are a morphologically and ecologically diverse hydrozoan suborder, currently including about 200 species.Being grouped in two clades, Corynida and Zancleida, these hydrozoans still show a number of taxonomic uncertainties at the species,genus and family levels. Many Capitata species established symbiotic relationships with other benthic organisms, including bryozoans,other cnidarians, molluscs and poriferans, as well as with planktonic dinoflagellates for mixotrophic relationships and with bacteria forthiotrophic ectosymbioses. Our study aimed at providing an updated and comprehensive phylogeny reconstruction of the suborder, atmodelling the evolution of selected morphological and ecological characters, and at testing evolutionary relationships between the sym-biotic lifestyle and the other characters, by integrating taxonomic, ecological and evolutionary data. The phylogenetic hypotheses herepresented shed light on the evolutionary relationships within Capitata, with most families and genera being recovered as monophyletic.The genusZancleaand family Zancleidae, however, were divided into four divergent clades, requiring the establishment of the newgenusApatizancleaand the new combinations for species inZancleaandHalocorynegenera. The ancestral state reconstructionsrevealed that symbiosis arose multiple times in the evolutionary history of the Capitata, and that homoplasy is a common phenomenonin the group. Correlations were found between the evolution of symbiosis and morphological characters, such as the perisarc. Overall,our results highlighted that the use of genetic data and a complete knowledge of the life cycles are strongly needed to disentangle taxo-nomic and systematic issues in capitate hydrozoans. Finally, the colonization of tropical habitat appears to have influenced the evolu-tion of a symbiotic lifestyle, playing important roles in the evolution of the group.