The Zancleidae is a hydrozoan family that currently comprises three genera and 42 nominal species. The validity of numerous taxa in this family still needs to be assessed with integrative analyses and complete life cycle descriptions. The vast majority of its species live symbiotically with other organisms, among which cheilostomate bryozoans are the most common hosts. These bryozoan-associated zancleids are host-specific and encompass all species of the genera Halocoryne and Zanclella, as well as several species in the genus Zanclea. Zancleids show variable morphologies, including highly reduced polyps and medusae. Their phylogenetic history is uncertain due to the often intergrading morphologies and the shortage of molecular data. In the present study, two species of Zanclea from the Indian Ocean and the Red Sea are analysed, using morphological and DNA-based approaches. Morphological analyses of the polyp and medusa stages show that, despite a general resemblance with each other and with Zanclella diabolica, the two species differ in some characters, and this is supported also by molecular investigations. The DNA analyses show that the two species are monophyletic and closely related, but divergent from other Zanclea lineages. This newly recovered clade may correspond with the genus Zanclella or with a cryptic genus. The lack of both morphological and molecular data for several zancleid species did not allow to address this issue. Additionally, the single-and multi-locus phylogeny reconstructions reveal that both the family Zancleidae and the genus Zanclea are polyphyletic taxa, since they are composed of at least three divergent lineages. Most zancleid species have polyps and medusae similar to other closely related taxa, and this conserved general morphology poses a challenge in the delimitation of species, genera and even families in this group. Consequently, further conjunct morphological and molecular efforts are strongly needed to clarify the diversity and evolution of the family Zancleida as a whole.
The phylogenetic relationships of the scleractinian genus Psammocora with the other genera traditionally included in the family Siderastreidae and some Fungiidae are assessed based on combined skeletal and molecular data. P. explanulata differs from the other examined congeneric species (P. contigua, P. digitata, P. nierstraszi , P. profundacella, P. superficialis, and P. stellata) in possessing interstomatous septa between adult corallites, costae, and in having continuous buttress-like structures joining septal faces (i.e., fulturae) which typically occur in fungiids. These characters are shared with Coscinaraea wellsi but not with the remainder of the examined siderastreids (the congeneric C. columna, and Anomastraea irregularis, Horastrea indica, Pseudosiderastrea tayamai, Siderastrea savignyana) whose septa are interconnected by typical synapticulae. Most of the examined species form septa with distinct transverse groups of centers of calcification, a biomineralization pattern typical of the Robusta clade. The observations on skeletal structures corroborate the results of the ITS2 and 5.8S molecular phylogeny. C. wellsi and P. explanulata are phylogenetically very close to each other and show closer genetic affinity with the examined Fungiidae (Halomitra pileus, Herpolitha limax, Fungia paumotensis, and Podabacia crustacea) than with the other species in the genera Psammocora and Coscinaraea, or with any other siderastreid. Our results show that neither Psammocora nor Coscinaraea are monophyletic genera. The high genetic distances between the species of Siderastreidae, especially between Pseudosiderastrea tayamai and Siderastrea savignyana on one side and the other genera on the other, suggest a deep divergence in the phylogenetic structure of the family.
An integrated approach using morphological and genetic data is needed to disentangle taxonomic uncertainties affecting the hydrozoan families Sphaerocorynidae and Zancleopsidae. Here we used this approach to accurately characterise species in these families, identify the previously unknown polyp stages of the genera Euphysilla and Zancleopsis, which were originally described exclusively based on the medusa stages, describe a new sphaerocorynid genus and species, and assess the phylogenetic position of the two families within the Capitata. The monotypic genus Astrocoryne was found to be a synonym of Zancleopsis. Astrocoryne cabela was therefore transferred to the genus Zancleopsis as Zancleopsis cabela comb. nov. The new polyp-based genus and species Kudacoryne diaphana gen. nov. sp. nov. was erected within the Sphaerocorynidae. Both taxa are primarily based on genetic data, but the introduction of this new genus was made necessary by the fact that it clustered with the genera Heterocoryne and Euphysilla, despite showing Sphaerocoryne-like polyps. Interestingly, the species analysed in this work showed contrasting biogeographical patterns. Based on our data and literature records, some species appear to have a wide circumtropical range, whereas others are limited to few localities. Overall, these results lay the ground for future investigations aimed at resolving the taxonomy and systematics of these two enigmatic families.