Polyphyly of the traditional family Flabellinidae affects a major group of Nudibranchia: aeolidacean taxonomic reassessment with descriptions of several new families, genera, and species (Mollusca, Gastropoda)

Abstract

The Flabellinidae, a heterogeneous assembly of supposedly plesiomorphic to very derived sea slug groups, have not yet been addressed by integrative studies. Here novel material of rarely seen Arctic taxa as well as North Atlantic, North and South Pacific, and tropical Indo-West Pacific flabellinid species is investigated morpho-anatomically and with multi-locus markers (partial COI, 16S rDNA, 28S rDNA and H3) which were generated and analysed in a comprehensive aeolid taxon sampling. It was found that the current fam- RESEARCH ARTICLE Launched to accelerate biodiversity research A peer-reviewed open-access journalTatiana Korshunova et al. / ZooKeys 717: 1-139 (2017) 2 ily Flabellinidae is polyphyletic and its phylogeny and taxonomic patterns cannot be understood without considering members from all the Aeolidacean families and, based on a robust phylogenetic hypothesis, morpho-anatomical evolution of aeolids is more complex than suspected in earlier works and requires reclassification of the taxon. Morphological diversity of Flabellinidae is corroborated by molecular divergence rates and supports establishing three new families (Apataidae fam. n., Flabellinopsidae fam. n., Samlidae fam. n.), 16 new genera, 13 new species, and two new subspecies among the former Flabellinidae. Two families, namely Coryphellidae and Paracoryphellidae, are restored and traditional Flabellinidae is considerably restricted. The distinctness of the recently described family Unidentiidae is confirmed by both morphological and molecular data. Several species complexes among all ex-"Flabellinidae" lineages are recognised using both morphological and molecular data. The present study shows that Facelinidae and Aeolidiidae, together with traditional "Tergipedidae", deeply divide traditional "Flabellinidae." Diagnoses for all aeolidacean families are therefore provided and additionally two new non-flabellinid families (Abronicidae fam. n. and Murmaniidae fam. n.) within traditional tergipedids are established to accommodate molecular and morphological disparity. To address relationships and disparity, we propose a new family system for aeolids. Here the aeolidacean species are classified into at least 102 genera and 24 families. Operational rules for integration of morphological and molecular data for taxonomy are suggested.

Multiple paedomorphic lineages of soft-substrate burrowing invertebrates: parallels in the origin of Xenocratena and Xenoturbella

“…Because during ontogeny of nudibranchs the number of ceratal rows gradually increases [79,80], and because the common ancestor of all aeolidacean possessed a large number of ceratal rows [19] it then follows that the small number of ceratal rows in Xenocratena only corresponds to juvenile stages of a common ancestor of the clade (Figs 1 and 4) consisting of the small Xenocratena (commonly less than 10 mm, maximum 12 mm adult length) and large Murmaniidae (up to 46 mm adult length). Basal members of the unrelated aeolidacean families Aeolidiidae and Paracoryphellidae are also large-sized (adults up to 50 mm or more) with numerous ceratal rows and demonstrate considerable external similarities to the complex Murmaniidae [19]. This is evidence that such organisation is plesiomorphic in aeolidaceans and also fulfills the first (morphological) criterion for assessing paedomorphosis.…”

“…Bayesian Inference (BI) and Maximum Likelihood (ML) analyses based on the combined dataset yielded trees with identical topologies (Fig 1). Surprisingly, Xenocratena was placed in a sister clade (PP = 1, BS = 100%) with the morphologically very different complex family Murmaniidae from the Arctic [19,76] (Figs 1-4), and not with the externally highly similar family, Cumanotidae (Figs 1 and 2F and 2I), from the same localities.…”

“…A subgroup of nudibranchs, treated here as suborder Aeolidacea, has evolved a defensive system for the secondary usage of cnidocysts from cnidarian prey [17,18]. While the phylogeny of Aeolidacea is currently actively studied [18][19][20][21], a majority of these nudibranchs as defined within the previously established broad-scope aeolidacean nudibranch phylogenetic framework [19], are complex animals with numerous dorsal papillae (cerata) (Figs 1-3). However, there is a single exclusively infaunal family, Pseudovermidae, with evident paedomorphic features such as vermiform shape and reduced dorsal papillae, which strongly matches early ontogenetic stages of complex aeolidaceans [22].…”

Second survey of heterobranch sea slugs (Mollusca, Gastropoda, Heterobranchia) from Bunaken National Park, North Sulawesi, Indonesia - how much do we know after 12 years?

“…11 because of the less narrowed cerata apices. Korshunova et al (2017) recently published a thorough investigation of Flabellinidae, transferring several Flabellina species into different genera and splitting the Flabellinidae in several different families. These new species affiliations apply to Flabellina exoptata (Fig.…”

Description of a new Moridilla species from North Sulawesi, Indonesia (Mollusca: Nudibranchia: Aeolidioidea)—based on MicroCT, histological and molecular analyses

“…Mitochondrial cytochrome c oxidase subunit I (COI) and 16S rRNA were sequenced for 12 Moridilla specimens and seven specimens belonging to Facelinidae (Table 1). Based on the results of Korshunova et al (2017) and Goodheart et al (2018) with regard to paraphyly of Facelinidae and outgroup results, we retrieved all available sequences of Facelinidae and Aeolidiidae from GenBank. According to the published phylogenetic analyses we chose available sequences of Unidentia and some Flabellinoidea as outgroup.…”