Diversity, host specificity and biogeography in the Cladocorynidae (Hydrozoa, Capitata), with description of a new genus

Abstract

The hydrozoan family Cladocorynidae inhabits tropical to temperate waters and comprises the two genera Pteroclava and Cladocoryne. Pteroclava lives in association with some octocorals and hydrozoans, whereas Cladocoryne is more generalist in terms of substrate choice. This work provides a thorough morpho-molecular reassessment of the Cladocorynidae by presenting the first well-supported phylogeny of the family based on the analyses of three mitochondrial and four nuclear markers. Notably, the two nominal genera were confirmed to be monophyletic and both morphological and genetic data led to the formal description of a new genus exclusively associated with octocorals, Pseudozanclea gen. nov. Maggioni & Montano. Accordingly, the diagnosis of the family was updated. The ancestral state reconstruction of selected characters revealed that the symbiosis with octocorals likely appeared in the most recent common ancestor of Pteroclava and Pseudozanclea. Additionally, the presence of euryteles aggregation in the polyp stage and the exumbrellar nematocyst pouches with euryteles represent synapomorphies of all cladocorynid taxa and probably emerged in their most recent common ancestor. The analysis of several Pteroclava krempfi colonies from Indo-Pacific and Caribbean localities associated with several host octocorals revealed a high intra-specific genetic variability. Single-and multi-locus species delimitations resulted in three to five species hypotheses, but the statistical analysis of morphometric data showed only limited distinction among the clades of P. krempfi. However, P. krempfi clades showed differences in both host specificity, mostly at the octocoral family level, and geographic distribution, with one clade found exclusively in the Caribbean Sea and the others found in the Indo-Pacific.

Systematics and character evolution of capitate hydrozoans

“…This large variability, together with the common intergrading morphologies between species, genera and even families, hamper the understanding of both taxonomy and evolution of several hydrozoan taxa. However, the use of molecular data to test the evolution of morphological and ecological traits has proven very useful in different taxa, highlighting the frequent presence of convergent and parallel evolutionary patterns (Leclère et al., 2007, 2009; Cartwright and Nawrocki, 2010; Maggioni et al., 2022a, b). Indeed, despite the presence of synapomorphies characterizing many taxa, homoplasy is quite a common phenomenon in hydrozoans, as demonstrated by, among others, the reduction of the medusa stage, the presence of polymorphic polyps and the colony type (Cartwright and Nawrocki, 2010).…”

“…Indeed, many species establish symbiotic relationships with other benthic organisms, living on or partially embedded in their hosts, which can be algae, crustaceans, bryozoans, molluscs, polychaetes, poriferans, or other cnidarians such as scleractinian corals and octocorals (Puce et al., 2008). The host specificity of these symbiotic species is variable, with both generalist and specialist taxa (Maggioni et al., 2022a, b), and in some cases the relationships appear to be very intimate, with the hosts showing specific structural modifications (Puce et al., 2005; Manca et al., 2019; Maggioni et al., 2020b). Both mutualistic and parasitic associations are known, with some species in the genus Zanclea Gegenbaur, 1856, for example, protecting their hosts from predators (Osman and Haugsness, 1981; Montano et al., 2017) and at least one Halocoryne species feeding on the lophophores of the host bryozoans (Piraino et al., 1992).…”

“…Despite several taxonomic and systematic issues being clarified by Nawrocki et al (2010), some relationships are still uncertain and many genera and species are currently lacking DNA data. Zancleida, on the other hand, shows a greater family and genus diversity, and some recent works focused on the diversity and evolution of certain families or clades (Miglietta et al, 2019;Maggioni et al, 2021Maggioni et al, , 2022b. A striking example of taxonomic and systematic uncertainties in Zancleida is represented by the family Zancleidae Russell, 1953, the most diverse of the clade, which has been demonstrated to be polyphyletic and to contain several cryptic species (Maggioni et al, 2018(Maggioni et al, , 2020a(Maggioni et al, , 2022a.…”

“…The geographical distribution of Capitata as a whole is circumglobal, from polar to tropical regions and from shallow to deep waters (Peña Cantero et al, 2013;Ronowicz et al, 2013;Montano et al, 2015a;Mastrototaro et al, 2016), with some species showing wide distributional ranges, and others only known from restricted localities (e.g. Maggioni et al, 2017Maggioni et al, , 2021Maggioni et al, , 2022bMiglietta et al, 2019).…”

The First Deep-Sea Stylasterid (Hydrozoa, Stylasteridae) of the Red Sea

“…Partition schemes and models for the concatenated dataset were determined with PartitionFinder 1.1.1 [50] using the Akaike information criterion, resulting in partitioning by DNA region and applying the GTR + I + G model to all partitions. Phylogenetic inference was performed using maximum likelihood (ML), maximum parsimony (MP), and Bayesian inference (BI) with RAxML 8.2.12 [51], PAUP 4.0b10 [52], and MrBayes 3.2.6 [53], respectively, as described in Maggioni et al [54].…”