Irina Ekimova

A Radical Solution: The Phylogeny of the Nudibranch Family Fionidae

Tergipedidae represents a diverse and successful group of aeolid nudibranchs, with approximately 200 species distributed throughout most marine ecosystems and spanning all biogeographical regions of the oceans. However, the systematics of this family remains poorly understood since no modern phylogenetic study has been undertaken to support any of the proposed classifications. The present study is the first molecular phylogeny of Tergipedidae based on partial sequences of two mitochondrial (COI and 16S) genes and one nuclear gene (H3). Maximum likelihood, maximum parsimony and Bayesian analysis were conducted in order to elucidate the systematics of this family. Our results do not recover the traditional Tergipedidae as monophyletic, since it belongs to a larger clade that includes the families Eubranchidae, Fionidae and Calmidae. This newly recovered clade is here referred to as Fionidae, the oldest name for this taxon. In addition, the present molecular phylogeny does not recover the traditional systematic relationships at a generic level, and therefore, systematic changes are required. We recognize the following clades within Fionidae: Calma, Cuthona, Cuthonella, Eubranchus, Fiona, Murmania, Tenellia, Tergipes, Tergiposacca gen. nov., Rubramoena gen. nov. and Abronica gen. nov. The type species of Tergiposacca, T. longicerata nov. sp. is described. The other two new genera have a previously described species as their type species. Most of these taxa, with the exceptions of Eubranchus, Tergipes and Fiona are composed of radically different constituent species from their traditional membership, but appear to be supported by morphological synapomorphies as well as molecular data. Aenigmastyletus, Catriona, Phestilla, Tenellia and Trinchesia are nested within other clades and, thus are here considered as synonyms of the larger clades. The phylogenetic position and validity of Myja, Guyvalvoria, Leostyletus and Subcuthona still need to be tested in future studies when material becomes available.

The structure of cnidosacs in nudibranch mollusc Aeolidia papillosa (Linnaeus, 1761) and presumable mechanism of nematocysts release

The structure of cnidosacs in nudibranch mollusc Aeolidida papillosa (Linnaeus, 1761) before and after the discharging of kleptocnidae has been studied. In the apical zone of the cnidosac, the basal laminae of epidermis and gastrodermis are interrupted, and the muscle layers of the cnidosac and the epidermis are absent. We suggest the formation of a temporary channel during the discharging of the cnidosac. Through this channel, nematocysts move from the cnidosac to the cnidopore, which forms on the top of the ceras.

Progenesis in the evolution of the nudibranch mollusks genus Dendronotus (Gastropoda: Nudibranchia)

The morphology and postlarval ontogenesis of the radula in 11 species of the genus Dendronotus Alder et Hancock, 1845, has been studied. Four types of radula are recognized in adult mollusks. Proposed evidence suggests that small species of Dendronotus have evolved by progenesis.

Living with a giant parchment tube worm: a description of a new nudibranch species (Gastropoda: Heterobranchia) associated with the annelid Chaetopterus

Small fionid nudibranch specimens collected within a Chaetopterus sp. tube worm are described here as a new species Tenellia chaetopterana sp. nov. This case is the first example of symbiotic association between a mollusk and an annelid host amongst cladobranch sea slugs. The external morphology of this species suggests it is adapted for living inside the worm’s tube: flattened body, laterally directed cerata and rhinophores, and wide foot. Molecular data, including partial sequences of mitochondrial COI and 16S and nuclear H3 genes, indicates that this species is distinct from other members of the genus Tenellia as well as other fionids. The species is close to the coral-feeding fionids of the genus Tenellia (formerly in genus Phestilla) in several morphological characters such as general radula morphology, absence of cnidosacs, and flattened body shape, as well as by molecular data. Tenellia chaetopterana sp. nov. has unique biology, implicating possible diversity previously overlooked by nudibranch faunistic studies.