Glass sponges (Hexactinellida) are key structural components of deep-sea ecosystems, often harboring diverse invertebrates. Yet associations with molluscs, and particularly the vermiform, shell-less Solenogastres (Mollusca, Aplacophora), remain virtually undocumented. The genus Apodomenia is exceptional among solenogasters in completely lacking a foot and pedal groove, a feature that departs from the traditional morphological distinctions separating solenogasters and caudofoveates, the other aplacophoran lineage. Until now, the genus was represented by a single species, A. enigmatica described from the Southern Ocean living in association with the hexactinellid sponge Rossella sp. Here we describe Apodomenia mimica sp. nov., based on the study of two specimens discovered in the hexactinellid Euplectella suberea in the Northwest Atlantic Ocean on the Mississippi-Alabama continental slope (USA). The new species exhibits striking camouflage, mimicking the fibrous skeleton of its host. These findings extend the ecological and geographic range of Apodomenia and indicate that different genera of hexactinellid sponges may harbor specialized but overlooked molluscan associates. Notably, a second solenogaster species was also recovered from the same sponge, suggesting for the first time the co-occurrence of multiple solenogaster lineages within a single host. Taken together, this work highlights glass sponges as reservoirs of overlooked biodiversity.

Freshwater gastropods are among the most imperiled organisms globally, and taxonomic uncertainty remains a major obstacle to their conservation. Elimia melanoides (Conrad, 1834), previously presumed extinct, was rediscovered in the Black Warrior River drainage of Alabama, prompting renewed interest in its conservation status. However, persistent taxonomic uncertainty has hindered listing under the U.S. Endangered Species Act. We used integrative taxonomy-including extensive field sampling, 3RAD-based phylogenomics, and morphological analysis of museum specimens-to resolve the taxonomy of E. melanoides sensu lato. Our molecular phylogenetic analyses revealed that E. melanoides, as currently conceived, comprises three distinct lineages: E. melanoides sensu stricto, Elimia hydeii (Conrad, 1834) (in part), and Elimia turgida (Haldeman, 1840), which we restore from synonymy. Comparison to historical museum specimens indicates that the extant lineage currently identified as E. melanoides is not conspecific with the taxon described as Anculosa melanoides by Conrad. We propose to follow prevailing usage and retain the name E. melanoides for the extinct taxon described by Conrad. There is no available name for the extant taxon, which we describe here as Elimia mintoni n. sp. Population genomic analyses revealed high genetic structure in E. mintoni n. sp. and E. hydeii, especially in headwater populations, while E. turgida showed no structure across its narrow range but maintains high genetic diversity. These findings have urgent conservation implications: E. mintoni n. sp. and E. turgida are valid, range-restricted species with low redundancy and representation. Our study underscores the necessity of taxonomic resolution for accurate biodiversity assessments and effective conservation planning.

We describe a new species of Solenogastres in the family Dondersiidae, Nematomenia quattriniae sp. nov., using an integrative taxonomic approach. The species is characterized by a slender, light-yellow body with a scaly appearance and dorsal keel, prominent anterior pedal glands, a dorsal foregut gland, a single dorso-terminal sensory organ, and the presence of seminal receptacles and seminal vesicles. Specimens were collected from a bathyal site (581 m depth) on the continental slope off Louisiana (USA) associated with the hydrozoan Acryptolaria abies (Allman, 1877), which displayed signs of an active defense response. This study sheds light on the trophic ecology of solenogasters and highlights the continued discovery of novel biodiversity and predator-prey interactions in deep-sea ecosystems.

This study provides an update on the non-native succineid (amber snail) species established in the Hawaiian Islands, with a focus on resolving taxonomic ambiguities and expanding the understanding of their distributions and potential impacts. Surveys across the Hawaiian Archipelago, coupled with morphological and genetic data, identified three non-native succineid species currently established in Hawai'i : Succinea costaricana, S. luteola, and S. unicolor. Additionally, a fourth species, Novisuccinea lyrata, intercepted at quarantine facilities, has not yet become established in the islands. Using integrative taxonomy, including DNA sequencing, shell morphology, and comparison with type materials, this research clarifies the identities of these species, correcting prior misidentifications, particularly of S. unicolor, which was previously confused with S. tenella, a species yet to be recorded in Hawai'i. The study also reveals a new invasion of S. luteola and documents the range expansion of S. costaricana within Hawai'i. These findings have significant biosecurity implications, as accurate species identification is crucial for effective quarantine measures. Furthermore, the introduction of these snails to sensitive environments like the Hawaiian Islands presents a risk of unanticipated ecological consequences, such as the spread of zoonotic disease agents. This research highlights the critical role precise taxonomic knowledge plays in preventing economic losses from species misidentifications in international trade. The study further underscores the complexity of managing non-native species invasions, particularly in island ecosystems with limited native species resilience, and for understudied taxa like snails.

Solenogastres (Mollusca, Aplacophora) are a unique and understudied group of marine invertebrates of evolutionary and ecological significance. Their diversity remains underestimated due to frequent lack of identification by non-specialists, limited molecular data, and the complexity of their taxonomy. Here we present the first Solenogastres from Puerto Rico, expanding the group’s known geographic distribution in the Caribbean Sea. Using an integrative taxonomic approach, we describe two new species, Dorymenia gummi sp. nov. and Strophomenia boricua sp. nov., and document their associations with coral hosts. These findings offer new insights into the ecology and biodiversity of these elusive mollusks.

Eyes within the marine gastropod superfamily Stromboidea range widely in size, from 0.2 to 2.3 mm, the latter being the largest known eyes of any gastropod. However, the evolutionary pressures underlying this variation remain unknown. Here, we use the wealth of material available in museum collections to explore the impact of ecological factors that affect light availability (ocean depth, turbidity and diel activity) on the evolution of eye size and structure within Stromboidea. We construct the most taxonomically extensive phylogeny of Stromboidea to date as a framework to investigate these relationships. Our results suggest that depth is a key light-limiting factor in stromboid eye evolution; here, increasing water depth is correlated with increasing aperture width relative to lens diameter (p = 0.043), and therefore an increasing investment in sensitivity in dim light environments. In the clade containing all large-eyed families (Strombidae, Rostellariidae and Seraphsidae), cathemeral species had wider eye apertures relative to lens sizes than diurnal species (p = 0.002), thereby prioritising sensitivity over resolution. These cathemeral species also had smaller body sizes than diurnal species (p = 0.002); this may suggest that animals with smaller shells are more vulnerable to shell-crushing predators, and therefore avoid the higher predation pressure experienced by animals active during the day. Within the large-eyed stromboid clade, ancestral state reconstruction estimates that absolute eye size increased above 1 mm twice independently. Due to the high energetic investment associated with large eye sizes, this repeated increase in eye size suggests that higher performance vision is important in behavioural tasks within these families. In addition, we note that species with more robust escape responses tend to have larger eyes than those that do not: for example, strombids have 1.79 times the eye size that would be expected from their body size (based on Stromboidea as a whole) and are known to display either a rapid escape response from an approaching predator or withdrawal into the shell. By contrast, the small-eyed xenophorids have 0.59 times the expected eye size, and are only known to withdraw when threatened.

Members of the radially ribbed mytilid genus Brachidontes are often dominant filter feeders on hard intertidal substrata in the Indo-Pacific region. However, there is still a great deal of uncertainty and confusion over their species identities, taxonomy and phylogenetic relationships. At least six species names ( crebris- triatus, karachiensis, mutabilis, pharaonis, ustulatus and variabilis) have at one time or another been synonymized with each other and applied to these common intertidal mussels. They occur widely across the Indian and Pacific Oceans from East Africa to Hawaii. Our results, based on sequences of five genes and anatomical features, suggest there are at least eight closely related sibling species in three monophyletic clades: (1) Brachidontes variabilis-form A in the western Indian Ocean; (2) Brachidontes pharaonis in the Red Sea; (3) Brachidontes variabilis-form B, found from India to East Asia; (4) Brachidontes mutabilis, restricted to southern Japan and China; (5) Brachidontes crebristriatus, in the Indian Ocean through to Southeast Asia and Hawaii; (6) Brachidontes ustulatus, an endemic species in western and southern Australia; (7) Brachidontes maritimus, so far known only from Hawaii; and (8) Brachidontes erosus, a southern Australian endemic. The latter two species form a small clade (Clade 1) that is sister to two larger Clades 2 and 3, each comprising three species. Clade 2 contains Brachidontes crebristriatus, Brachidontes mutabilis and Brachidontes ustulatus, whilst Clade 3 is made up of Brachidontes pharaonis, Brachidontes variabilis-form A and variabilis-form B. The shells of these eight species are not only variable but can greatly overlap in morphology. Many are also nearly impossible to distinguish without geographical information. However, the absence or presence of plicate organs in the mantle cavity, and the shape of guard papillae lining the inhalant aperture, may serve as important diagnostic morphological characters when used alongside geographical provenance.

The superfamily Stromboidea is a clade of morphologically distinctive gastropods which include the iconic Strombidae, or 'true conchs'. In this study, we present the most taxonomically extensive phylogeny of the superfamily to date, using fossil calibrations to produce a chronogram and extant geographical distributions to reconstruct ancestral ranges. From these results, we confirm the monophyly of all stromboidean families; however, six genera are not monophyletic using current generic assignments (Strombidae: Lentigo, Canarium, Dolomena, Doxander; Xenophoridae: Onustus, Xenophora). Within Strombidae, analyses resolve an Indo-West Pacific (IWP) clade sister to an East Pacific/Atlantic clade, together sister to a second, larger IWP clade. Our results also indicate two pulses of strombid diversification within the Miocene, and a Tethyan/IWP origin for Strombidae-both supported by the fossil record. However, conflicts between divergence time estimates and the fossil record warrant further exploration. Species delimitation analyses using the COI barcoding gene support several taxonomic changes. We synonymise Euprotomus aurora with Euprotomus bulla, Strombus alatus with Strombus pugilis, Dolomena abbotti with Dolomena labiosa, and Dolomena operosa with Dolomena vittata. We identified cryptic species complexes within Terebellum terebellum, Lambis lambis, "Canarium" wilsonorum, Dolomena turturella and Maculastrombus mutabilis. We reinstate Rimellopsis laurenti as a species (previously synonymised with R. powisii) and recognise Harpago chiragra rugosus and Lambis truncata sowerbyi valid at the rank of species. Finally, we establish several new combinations to render Lentigo, Dolomena, and Canarium monophyletic: Lentigo thersites, Dolomena robusta, Dolomena epidromis, Dolomena turturella, Dolomena taeniata, Dolomena vanikorensis, D. vittata, "Canarium" wilsonorum, Hawaiistrombus scalariformis, Maculastrombus mutabilis, Maculastrombus microurceus.

Interspecific hybridization can lead to myriad outcomes, including transgressive phenotypes in which the hybrids are more fit than either parent species. Such hybrids may display important traits in the context of climate change, able to respond to novel environmental conditions not previously experienced by the parent populations. While this has been evaluated in an agricultural context, the role of transgressive hybrids under changing conditions in the wild remains largely unexplored; this is especially true regarding transgressive gene expression. Using the blue mussel species complex (genus Mytilus) as a model system, we investigated the effects of hybridization on temperature induced gene expression plasticity by comparing expression profiles in parental species and their hybrids following a 2-week thermal challenge. Hybrid expression plasticity was most often like one parent or the other (50%). However, a large fraction of genes (26%) showed transgressive expression plasticity (i.e. the change in gene expression was either greater or lesser than that of both parent species), while only 2% were intermediately plastic in hybrids. Despite their close phylogenetic relationship, there was limited overlap in the differentially expressed genes responding to temperature, indicating interspecific differences in the responses to high temperature in which responses from hybrids are distinct from both parent species. We also identified differentially expressed long non-coding RNAs (lncRNAs), which we suggest may contribute to species-specific differences in thermal tolerance. Our findings provide important insight into the impact of hybridization on gene expression under warming. We propose transgressive hybrids may play an important role in population persistence under future warming conditions.

Target-capture approaches have facilitated a rapid growth in the field of phylogenomics but few probe sets exist for molluscs, an exceptionally rich phylum with unparalleled ecological and morphological diversity. We designed and tested the first universal probe set using Phyluce to capture ultraconserved elements (UCEs) and exon loci from the Subclass Caenogastropoda - one of six major lineages of gastropods. The probe set consists of 29,441 probes designed to target 1142 UCE loci and 1933 exon loci (3075 total). In silico analyses of our probe set yielded an average of 2110 loci from genomes and 1389 loci from transcriptomes of diverse caenogastropods, from which an average of 1669 and 849 loci were retained respectively after screening to remove those that matched multiple contigs. Phylogenetic analyses of the loci extracted from transcriptomes produced well-supported trees very similar to those published based on transcriptomic analyses. Phylogenetic relationships estimated from loci extracted from genomes recover similar phylogenetic relationships, and indicate that the loci targeted with this probe set are informative for resolving deep phylogenetic relationships. An in vitro analysis of the probe set with the Epitoniidae, a diverse caenogastropod family of uncertain affinity and with poorly resolved evolutionary relationships, recovered a total of 2850 loci. Although preliminary, the analysis of loci captured by our probe set for a small number of epitoniid taxa produced a well-resolved tree indicating that this probe set is also able to resolve relationships at shallower hierarchical scales. Together, the in silico and in vitro analyses indicate that target-capture enrichment with this probe set is a useful tool for reconstructing phylogenetic relationships across taxonomic levels and evolutionary time scales.

The Pacificellinae are a group of small, high-spired land snails distributed on islands across the Pacific. Some species are endemic to particular island groups, but others have wide geographic distributions, several of which have been attributed to anthropogenic transport between islands before western contact. We used DNA sequence data (COI, 16S, ITS2, 28S) from recently collected and historical specimens to estimate a phylogeny of the Pacificellinae, with a focus on Hawaiian species. Phylogenetic analyses support recognizing Lamellidea and Pacificella as distinct genera and indicate that the genus group Tornatellinops should be regarded as a synonym of Lamellidea. The number of taxa defined by species delimitation analyses (ASAP, bPTP, mPTP) varies widely, with between 6 and 42 species estimated in the Hawaiian Islands. These candidate species hypotheses were evaluated in an integrative framework, including shell morphology, geography, and a multilocus phylogeny, to revise the taxonomy of Hawaiian pacificellines. Four Lamellidea species and two Pacificella species are recognized from the Hawaiian Islands, including two widespread species introduced to Hawaiʻi from the South Pacific. Lamellidea peponum in Hawaiʻi shows little genetic divergence from Polynesian specimens previously referred to L. oblonga, and the name L. oblonga is now regarded as a junior synonym. Lamellidea polygnampta is recognized here from across the Hawaiian Islands, L. cylindrica from the island of O‘ahu, and the lowland species, L. extincta, from the main Hawaiian Islands and the Northwestern Islands. The only Pacificella specimens found in Hawai‘i in modern surveys are more closely related to specimens of P. variabilis from Polynesia than to historical specimens of P. baldwini, indicating that the only Pacificella species now found in the main Hawaiian Islands appears to be introduced. Pacificellines have declined in abundance in Hawai‘i over the last century and the two species L. extincta and P. baldwini, formerly present across the Hawaiian Islands, are now either critically endangered or extinct.

Terrestrial gastropods are among the most imperiled groups of organisms on Earth. Many species have a complex taxonomic history, often including poorly defined subspecies, most of which have not been the focus of modern systematics research. Genomic tools, geometric morphometrics, and environmental niche modeling were used to assess the taxonomic status of Pateraclarkiinantahala (Clench & Banks, 1932), a subspecies of high conservation concern with a restricted range of approximately 3.3 km2 in North Carolina, USA. A genome-scale dataset was generated that included individuals with morphologies matching P.c.nantahala, P.c.clarkii, and one individual with an intermediate form between P.c.nantahala and P.c.clarkii that was initially hypothesized as a potential hybrid. Mitochondrial phylogenetics, nuclear species tree inference, and phylogenetic networks were used to assess relationships and gene flow. Differences in shell shape via geometric morphometrics and whether the environmental niches of the two subspecies were significantly different were also examined. Molecular analyses indicated an absence of gene flow among lineages of P.clarkii sensu lato. Analyses rejected our hypothesis that the intermediate shelled form represented a hybrid, but instead indicated that it was a distinct lineage. Environmental niche models indicated significant differences in environmental niche between P.c.clarkii and P.c.nantahala, and geometric morphometrics indicated that P.c.nantahala had a significantly different shell shape. Given multiple lines of evidence, species-level recognition of P.nantahala is warranted.

The Pacificellinae are a group of small, high-spired land snails distributed on islands across the Pacific. Some species are endemic to particular island groups, but others have wide geographic distributions, several of which have been attributed to anthropogenic transport between islands before western contact. We used DNA sequence data (COI, 16S, ITS2, 28S) from recently collected and historical specimens to estimate a phylogeny of the Pacificellinae, with a focus on Hawaiian species. Phylogenetic analyses support recognizing Lamellidea and Pacificella as distinct genera and indicate that the genus group Tornatellinops should be regarded as a synonym of Lamellidea. The number of taxa defined by species delimitation analyses (ASAP, bPTP, mPTP) varies widely, with between 6 and 42 species estimated in the Hawaiian Islands. These candidate species hypotheses were evaluated in an integrative framework, including shell morphology, geography, and a multilocus phylogeny, to revise the taxonomy of Hawaiian pacificellines. Four Lamellidea species and two Pacificella species are recognized from the Hawaiian Islands, including two widespread species introduced to Hawaiʻi from the South Pacific. Lamellidea peponum in Hawaiʻi shows little genetic divergence from Polynesian specimens previously referred to L. oblonga, and the name L. oblonga is now regarded as a junior synonym. Lamellidea polygnampta is recognized here from across the Hawaiian Islands, L. cylindrica from the island of O‘ahu, and the lowland species, L. extincta, from the main Hawaiian Islands and the Northwestern Islands. The only Pacificella specimens found in Hawai‘i in modern surveys are more closely related to specimens of P. variabilis from Polynesia than to historical specimens of P. baldwini, indicating that the only Pacificella species now found in the main Hawaiian Islands appears to be introduced. Pacificellines have declined in abundance in Hawai‘i over the last century and the two species L. extincta and P. baldwini, formerly present across the Hawaiian Islands, are now either critically endangered or extinct.

Phylogenomic studies with hundreds or thousands of loci are rare for most invertebrate groups, including freshwater gastropods. This can prevent understanding of phylogeny, which hinders many areas of research. Pleuroceridae is a family of freshwater snails that is highly imperiled and plays an essential role in the ecology of many freshwater systems of the eastern United States. However, the evolutionary history of the family is not understood, and the systematics of the family has not been revised in a modern framework. Pleurocerids display a variety of egg-deposition behaviors and shell shapes, making the family an ideal system for studying evolution of invertebrate life history and morphology. However, past mitochondrial-based phylogenetic analyses have failed to produce meaningful phylogenetic hypotheses, preventing conclusions about pleurocerid systematics and evolution. Here, we generated a novel anchored hybrid enrichment probe set with phylogenetic utility for Pleuroceridae. We sampled pleurocerids from across their range to test the probe set and generated a backbone phylogeny. Our analyses uncovered striking levels of polyphyly among currently accepted genera. Numerous species were also polyphyletic, indicative of unrecognized diversity. Phylogenetic patterns also revealed considerable convergence of shell morphologies. In contrast, anatomical and life history features appeared to be much less homoplastic. Despite generic paraphyly, high support for most major clades and phylogenetic cohesiveness of non-shell characters indicate utility of the AHE probe set for studying pleurocerid evolution.

Donacidae is a commercially important family of heterodont bivalves and one of the few bivalve lineages that has successfully colonised brackish and fresh waters. However, to date, no phylogenetic hypothesis exists for this widely distributed group. Here we turn to molecular data from the nuclear and mitochondrial genomes and combine these with the extensive fossil record of donacids to propose an evolutionary hypothesis for the family. Our analyses strongly support the monophyly of Donacidae, including Galatea, Iphigenia and ‘Plebidonax’ deltoides, but render Donax paraphyletic. The subgenus Latona is therefore elevated to genus to accommodate a clade of Indo-Pacific species, while retaining Donax for a clade of mostly Atlantic and American Pacific species, and a few Indo-Pacific species. This latter clade is sister group to Galatea + Iphigenia. The diversification of Donacidae seems to be tightly connected to the opening of the North and South Atlantic Oceans in the Cretaceous, and to the closing of the Tethys Ocean during the Oligocene. Taxonomic actions: Latona columbella (Lamarck, 1818) comb. nov., L. deltoides (Lamarck, 1818) comb. nov., L. dysoni (Reeve, 1854) comb. nov., L. madagascariensis (W. Wood, 1828) comb. nov., L. semisulcata semigranosa (Dunker, 1877) comb. nov., L. spinosa (Gmelin, 1791) comb. nov., L. sordida (Hanley, 1845) comb. nov., L. siliqua (Römer, 1870) comb. nov., L. trifasciata (Linnaeus, 1758) comb. nov. and L. victoris (Fischer-Piette, 1942) comb. nov.

The neogastropod family Columbellidae is a highly successful group of small, primarily epibenthic marine snails distributed worldwide and most abundant in the tropics. The great diversity of the group makes them attractive for studying evolutionary shifts in gastropod anatomy, morphology, ecology and diversity. The existing classification of the family has been based to a large degree on the morphology of the shell and radula. Indeed, membership in the family is traditionally confirmed using the unique morphology of the radula. To reconstruct columbellid phylogeny and assess monophyly of the group, we assembled a multilocus dataset including five mitochondrial and nuclear genes, for 70 species in 31 genera. Phylogenetic analyses using Bayesian inference and maximum likelihood are not well enough resolved to support a subfamilial classification, but do support the monophyly of the family and of several well-defined genera and supra-generic groupings. Two of the most diverse nominal genera, Mitrella and Anachis, are supported as highly polyphyletic. Overall, the resulting topologies indicate that the generic and subfamilial classification is in need of extensive revision but that phylogenomic data are needed to resolve columbellid relationships.

Gastropods have survived several mass extinctions during their evolutionary history resulting in extraordinary diversity in morphology, ecology, and developmental modes, which complicate the reconstruction of a robust phylogeny. Currently, gastropods are divided into six subclasses: Caenogastropoda, Heterobranchia, Neomphaliones, Neritimorpha, Patellogastropoda, and Vetigastropoda. Phylogenetic relationships among these taxa historically lack consensus, despite numerous efforts using morphological and molecular information. We generated sequence data for transcriptomes derived from 12 taxa belonging to clades with little or no prior representation in previous studies in order to infer the deeper cladogenetic events within Gastropoda and, for the first time, infer the position of the deep-sea Neomphaliones using a phylogenomic approach. We explored the impact of missing data, homoplasy, and compositional heterogeneity on the inferred phylogenetic hypotheses. We recovered a highly supported backbone for gastropod relationships that is congruent with morphological and mitogenomic evidence, in which Patellogastropoda, true limpets, are the sister lineage to all other gastropods (Orthogastropoda) which are divided into two main clades 1) Vetigastropoda $s.l.$ (including Pleurotomariida $+$ Neomphaliones) and 2) Neritimorpha $+$ (Caenogastropoda $+$ Heterobranchia). As such, our results support the recognition of five subclasses (or infraclasses) in Gastropoda: Patellogastropoda, Vetigastropoda, Neritimorpha, Caenogastropoda, and Heterobranchia. [Compositional heterogeneity; fast-evolving; long-branch attraction; missing data; Mollusca; phylogenetics; systematic error.]