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Solenogastres and Caudofoveata (Aplacophora) remain some of the least known molluscs, despite ubiquity in the marine environment and importance in understanding molluscan evolution. The use of new morphological techniques and development of DNA barcode libraries have helped make specimen identification easier. However, for solenogasters, using histology for identification and adequate description of species remains necessary in most cases. This, together with the facts that knowledge about solenogaster species distributions is biased and that most species were described from one or very few individuals, explains why many open questions about the actual distribution, intra- and interspecific variability, etc., remain. We performed an integrative taxonomic study of eight specimens of solenogasters from the South China Sea (West Pacific Ocean) thatresulted in the identification of four new species of Proneomeniidae. Species identification and description following the established diagnostic characters were straightforward. However, phylogenetic analysis of molecular data obtained from these specimens and other members of Proneomeniidae indicate that the family is polyphyletic. We recovered representatives of two other families, Epimeniidae (Epimenia) and Strophomeniidae (Anamenia), nested within Proneomeniidae with strong support. Ancestral character state reconstruction indicates that characters commonly used in solenogaster taxonomy, such as the radula and foregut glands, may be more evolutionarily labile in this group than previously known. Therefore our work fills knowledge gaps regarding the diversity and distribution of members of this family but raises important questions about solenogaster taxonomy and systematics that should be further assessed with additional markers and broader taxon sampling.
Norfolk Island harbours a rich land snail diversity dominated by the Microcystidae and Helicarionidae that are currently represented by 10 endemic genera and 27 accepted species and subspecies. We comprehensively revise the taxonomy of these taxa using comparative morphology and phylogenetic analyses of the mitochondrial genes COI and 16S. We demonstrate that most ‘helicarionid’ species belong to Microcystidae with only a single species of Helicarionidae present (Dendrolamellaria mathewsi). The Norfolk Island microcystids comprise five major clades. These clades may have independently colonised the Norfolk Island group; however, clarity may only be achieved in a broader phylogenetic context that incorporates the study of extralimital groups. Three clades have radiated in situ into multiple endemic species. Based on our findings, we recognise the previously accepted genera Iredaleoconcha, Nancibella and Roybellia as junior synonyms of Allenoconcha, and Mathewsoconcha and Quintalia as junior synonyms of Advena, based on the close phylogenetic relationships. Furthermore, we confirm the previous treatment of Lutilodix, Parcolena and Dolapex as junior synonyms of Fanulena and Belloconcha as a synonym of Advena, bringing the total number of Norfolk Island microcystid genera to five. Secondly, we provide revised descriptions for each of these genera. Thirdly, we remove Allenoconcha belli, A. mathewsi, A. monspittensis, A. perdepressa and A. royana from the synonymy with Allenoconcha basispiralis. We also remove Helix patescens from synonymy with Quintalia flosculus, treating this as a member of Allenoconcha, and resurrect Advena campbellii nepeanensis and Quintalia stoddartii intermedia as accepted subspecies. Based on comparative morpho-anatomy, we treat Allenoconcha mathewsi and A. monspittensis as junior synonyms of Allenoconcha royana, A. inopina as a junior synonym of Allenoconcha caloraphe, Fanulena fraternus as a junior synonym of F. amiculus, Advena campbellii charon as a synonym of Advena campbellii campbellii, Mathewsoconcha belli, M. compacta and M. norfolkensis as junior synonyms of Advena suteri, M. elevata as a junior synonym of Advena grayi, and M. microstriatum as a junior synonym of Advena phillipii. Lastly, we describe three new species, Allenoconcha evansorum sp. nov., A. margaretae sp. nov. and A. varmani sp. nov. In summary, we accept 27 microcystid species and subspecies all of which are endemic to the Norfolk Island group. We provide recent and historical distribution data for each species and demonstrate that seven species or subspecies are probably extinct. All species are well differentiated in terms of basal branch lengths in the phylogenetic tree, but this distinction is not consistently reflected in the external morphology. Some closely related sister-taxa are very similar in shell morphology whereas others exhibit highly distinctive shells. We hypothesise that these stark differences in shell morphology may result from adaptation to different ecological niches, yet we currently lack a detailed understanding of the underlying evolutionary mechanisms.
Ribbon worms (phylum Nemertea) are found in oceans worldwide; however, only a few inhabit terrestrial, semiterrestrial and freshwater environments. In our study, we describe Acteonemertes orientalis sp. nov., a new species of Plectonemertidae Gibson, 1990 and the first plectonemertid discovered in Japan. The species was found in the supralittoral zone, from which nemerteans have rarely been reported and inhabits areas under rocks, wave-dissipating concrete blocks, and fallen leaves and stocks, along the coast of the Sea of Japan. Multi-locus phylogenetic analyses based on two mitochondrial (16S rRNA and cytochrome c oxidase subunit I) and two nuclear gene markers (18S rRNA and 28S rRNA) revealed that A. orientalis sp. nov. formed a clade with Leptonemertes cf. chalicophora collected from Florida. Although the external and internal morphology of A. orientalis sp. nov. is largely consistent with the generic diagnosis, this species differs in having a large proboscis. Based on the molecular and morphological data, we propose to amend the diagnosis of Acteonemertes by excluding proboscis size.
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