Uncovering the shell game with barcodes: diversity of meiofaunal Caecidae snails (Truncatelloidea, Caenogastropoda) from Central America.

Caecidae is a species-rich family of microsnails with a worldwide distribution. Typical for many groups of gastropods, caecid taxonomy is largely based on overt shell characters. However, identification of species using shell characteristics is problematic due to their rather uniform, tubular shells, the presence of different growth stages, and a high degree of intraspecific variability. In the present study, a first integrative approach to caecid taxonomy is provided using light-microscopic investigation with microsculptural analyses and multi-marker barcoding, in conjunction with molecular species delineation analyses (ABGD, haplotype networks, GMYC, and bPTP). In total 132 specimens of Caecum and Meioceras collected during several sampling trips to Central America were analyzed and delineated into a minimum of 19 species to discuss putative synonyms, and supplement the original descriptions. Molecular phylogenetic analyses suggest Meioceras nitidum and M. cubitatum should be reclassified as Caecum, and the genus Meioceras might present a junior synonym of Caecum. Meiofaunal caecids morphologically resembling C. glabrum from the Northeast Atlantic are a complex of cryptic species with independent evolutionary origins, likely associated with multiple habitat shifts to the mesopsammic environment. Caecum invisibile Egger & Jörger, sp. nov. is formally described based on molecular diagnostic characters. This first integrative approach towards the taxonomy of Caecidae increases the known diversity, reveals the need for a reclassification of the genus Caecum and serves as a starting point for a barcoding library of the family, thereby enabling further reliable identifications of these taxonomically challenging microsnails in future studies.

An Antarctic flock under the Thorson's rule: Diversity and larval development of Antarctic Velutinidae (Mollusca: Gastropoda).

In most marine gastropods, the duration of the larval phase is a key feature, strongly influencing species distribution and persistence. Antarctic lineages, in agreement with Thorson's rule, generally show a short pelagic developmental phase (or lack it completely), with very few exceptions. Among them is the ascidian-feeding gastropod family Velutinidae, a quite understudied group. Based on a multilocus (COI, 16S, 28S and ITS2) dataset for 182 specimens collected in Antarctica and other regions worldwide, we investigated the actual Antarctic velutinid diversity, inferred their larval development, tested species genetic connectivity and produced a first phylogenetic framework of the family. We identified 15 Antarctic Molecular Operational Taxonomic Units (MOTUs), some of which represented undescribed species, which show two different types of larval shell, indicating different duration of the Pelagic Larval Phase (PLD). Antarctic velutinids stand as an independent lineage, sister to the rest of the family, with extensive hidden diversity likely produced by rapid radiation. Our phylogenetic framework indicates that this Antarctic flock underwent repeated events of pelagic phase shortening, in agreement with Thorson's rule, yielding species with restricted geographic ranges.

Delimiting species of marine gastropods (Turridae, Conoidea) using RAD sequencing in an integrative taxonomy framework.

Species delimitation in poorly known and diverse taxa is usually performed based on monolocus, DNA-barcoding-like approaches, while multilocus data are often used to test alternative species hypotheses in well-studied groups. We combined both approaches to delimit species in the Xenuroturris/Iotyrris complex, a group of venomous marine gastropods from the Indo-Pacific. First, COI sequences were analysed using three methods of species delimitation to propose primary species hypotheses. Second, RAD sequencing data were also obtained and a maximum-likelihood phylogenetic tree produced. We tested the impact of the level of missing data on the robustness of the phylogenetic tree obtained with the RAD-seq data. Alternative species partitions revealed with the COI data set were also tested using the RAD-seq data and the Bayes factor species delimitation method. The congruence between the species hypotheses proposed with the mitochondrial nuclear data sets, together with the morphological variability of the shell and the radula and the distribution pattern, was used to turn the primary species hypotheses into secondary species hypotheses. Allopatric primary species hypotheses defined with the COI gene were interpreted to correspond to intraspecific structure. Most of the species are found sympatrically in the Philippines, and only one is confidently identified as a new species and described as Iotyrris conotaxis n. sp. The results obtained demonstrate the efficiency of the combined monolocus/multilocus approach to delimit species.

Phylogenetic relationships of Mediterranean and North-East Atlantic Cantharidinae and notes on Stomatellinae (Vetigastropoda: Trochidae).

The subfamily Cantharidinae Gray, 1857 (Trochoidea: Trochidae) includes 23 recognized genera and over 200 known living species. These marine top shell snails are microphagous grazers that generally live in shallow rocky shores and in macroalgae and seagrass beds of sub-tropical and temperate waters from the Central and Western Indo-Pacific biogeographic regions to the Mediterranean Sea and the Eastern Atlantic Ocean. Recent molecular phylogenetic studies revising the family Trochidae supported the monophyly of the subfamily Cantharidinae and its sister group relationship to the subfamily Stomatellinae. These studies and others has thus far mostly focused on Indo-Pacific members of the subfamily Cantharidinae whereas here, we investigated phylogenetic relationships among their counterparts from the Mediterranean Sea and the North-eastern (NE) Atlantic Ocean including 33 species of genera Gibbula, Jujubinus, Phorcus, Clelandella, and Callumbonella. The Mediterranean and NE Atlantic taxa were supplemented with 30 Indo-Pacific Cantharidinae species plus 19 members of the sister group subfamily Stomatellinae. Phylogenetic trees were constructed using Bayesian inference and maximum likelihood with two datasets comprised of partial sequences of four or six mitochondrial (cox1, rrnL, rrnS, and cob) and nuclear (28S rRNA and histone H3) genes. A clade comprised of all Mediterranean and NE Atlantic taxa was recovered with high support, but its sister group among the Indo-Pacific lineages could not be determined with confidence (although the assignment of "Trochus" kotschyi to Priotrochus could be rejected). Within the Mediterranean and NE Atlantic clade, genera Phorcus and Jujubinus were recovered as reciprocally monophyletic, and the deep-sea genera Clelandella and Callumbonella were placed with high support as sister to Jujubinus. However, the genus Gibbula as currently defined was not monophyletic and constituent species were divided into three major clades and two independent lineages. Phylogenetic relationships among Phorcus, Jujubinus (plus Clelandella and Callumbonella), and the different clades of Gibbula were not fully resolved but received higher support in the phylogenetic analyses based on six genes. A first approach to resolve phylogenetic relationships within Stomatellinae was conducted showing that the diversity of the subfamily is highly underestimated at present, and that Calliotrochus is possibly a member of this subfamily. A chronogram was reconstructed using an uncorrelated relaxed lognormal molecular clock and the origin of the Mediterranean and NE Atlantic clade was dated right after the Azolla phase in the Middle Eocene about 48 million years ago whereas diversification of major clades (genera) followed the eastern closure of the Tethys Ocean in the Middle Miocene about 14 million years ago.

First molecular phylogeny of the circumtropical bivalve family Pinnidae (Mollusca, Bivalvia): evidence for high levels of cryptic species diversity.

The family Pinnidae Leach, 1819, includes approximately 50 species of large subtidal and coastal marine bivalves. These commercially important species occur in tropical and temperate waters around the world and are most frequently found in seagrass meadows. The taxonomy of the family has been revised a number of times since the early 20th Century, the most recent revision recognizing 55 species distributed in three genera: Pinna, Atrina and Streptopinna, the latter being monotypic. However, to date no phylogenetic analysis of the family has been conducted using morphological or molecular data. The present study analyzed 306 pinnid specimens from around the world, comprising the three described genera and ca. 25 morphospecies. We sequenced the mitochondrial genes 16S rRNA and cytochrome c oxidase subunit I, and the nuclear ribosomal genes 18S rRNA and 28S rRNA. Phylogenetic analysis of the data revealed monophyly of the genus Atrina but also that the genus Streptopinna is nested within Pinna. Based on the strong support for this relationship we propose a new status for Streptopinna Martens, 1880 and treat it as a subgenus (status nov.) of Pinna Linnaeus, 1758. The phylogeny and the species delimitation analyses suggest the presence of cryptic species in many morphospecies displaying a wide Indo-Pacific distribution, including Pinna muricata, Atrina assimilis, A. exusta and P. (Streptopinna) saccata but also in the Atlantic species A. rigida. Altogether our results highlight the challenges associated with morphological identifications in Pinnidae due to the presence of both phenotypic plasticity and morphological stasis and reveal that many pinnid species are not as widely distributed as previously thought.

Phylogenetic relationships elucidate colonization patterns in the intertidal grazers Osilinus Philippi, 1847 and Phorcus Risso, 1826 (Gastropoda: Trochidae) in the northeastern Atlantic Ocean and Mediterranean Sea.

Snails in the closely related trochid genera Phorcus Risso, 1826 and Osilinus Philippi, 1847 are ecologically important algal grazers in the intertidal zone of the northeastern Atlantic Ocean and Mediterranean Sea. Here we present the first complete molecular phylogeny for these genera, based on the nuclear 28S rRNA gene and the mitochondrial 16S rRNA and COI genes, and show that the current classification is erroneous. We recognize nine species in a single genus, Phorcus: estimated by BEAST analysis, this arose 30 (± 10) Ma; it consists of two subgenera, Phorcus and Osilinus, which we estimate diverged 14 (± 4.5) Ma. Osilinus kotschyi, from the Arabian and Red Seas, is not closely related and is tentatively referred to Priotrochus Fischer, 1879. Our phylogeny allows us to address biogeographical questions concerning the origins of the Mediterranean and Macaronesian species of this group. The former appear to have evolved from Atlantic ancestors that invaded the Mediterranean on several occasions after the Zanclean Flood, which ended the Messinian Salinity Crisis 5.3 Ma; whereas the latter arose from several colonizations of mainland Atlantic ancestors within the last 3 (± 1.5) Ma.

New insights into diversity and evolution of deep-sea Mytilidae (Mollusca: Bivalvia).

Bathymodiolinae mussels have been used as a biological model to better understand the evolutionary origin of faunas associated with deep-sea hydrothermal vents and cold seeps. Most studies to date, however, have sampled with a strong bias towards vent and seep species, mainly because of a lack of knowledge of closely related species from organic falls. Here we reassess the species diversity of deep-sea mussels using two genes and a large taxon sample from the South-Western Pacific. This new taxonomic framework serves as a basis for a phylogenetic investigation of their evolutionary history. We first highlight an unexpected allopatric pattern and suggest that mussels usually reported from organic falls are in fact poorly specialized with regard to their environment. This challenges the adaptive scenarios proposed to explain the diversification of the group. Second, we confirm that deep-sea mussels arose from organic falls and then colonized hydrothermal vents and cold seeps in multiple events. Overall, this study constitutes a new basis for further phylogenetic investigations and a global systematic revision of deep-sea mussels.