Freshwater gastropods in the family Pleuroceridae are important components of North American freshwater ecosystems that can greatly influence ecological processes and biotic communities. Elimia is the most taxa rich among pleurocerid genera. Elimia comalensisPilsbry, 1890, is the only pleurocerid species that occurs in Texas and is currently known to occupy artesian springs and spring-fed river systems associated with the Edwards Plateau region. Published literature on E. comalensis is limited, and little information is currently present regarding explicit patterns of distribution and abundance within most systems currently occupied. We examined temporal and spatial variation of E. comalensis densities in the upper San Marcos River from 2013 to 2016, as well as interspecific affinities between E. comalensis and two invasive thiarid snails. We observed significant annual differences in E. comalensis densities, with greater mean density occurring under low flow conditions in 2014. We also observed significant differences in densities among sites, with greater density occurring at sites with larger and more complex substratum particles. Elimia comalensis exhibited a strong positive relationship with the thiarid snail Tarebia granifera, although data suggest that interspecific competition is limited as these species co-occur at high densities. As anthropogenic impacts continue to impact Edwards Plateau spring systems, further research on the distribution and population dynamics of ecologically important pleurocerid snails, such as E. comalensis, is needed to aid in the conservation of these unique ecosystems.

The small, green sea hare, Phyllaplysia viridis, originally described from Indonesia in 1905, has rarely been recorded since. Because the taxonomic status of Phyllaplysia is uncertain, there remains a need for clarification of the currently accepted species. To do so, we used contemporary specimens from eastern Australia and Indonesia to redescribe P. viridis using photographs and scanning electron imagery of its external and internal morphology. Although all examined specimens were small, consistently green animals, images revealed some variation in colour and pattern among adults. Molecular data confirmed the presence of P. viridis in the Philippines, Indonesia and eastern Australia. A phylogenetic tree based on available COI barcode sequences illustrate a sister relationship with other Phyllaplysia. The construction of a haplotype network failed to show any marked geographic structure among specimens.

The original description of Helicina weyrauchiHaas, 1948, was based on shell material, as is the case for several helicinids in South America. We redescribe the species based on freshly collected material and provide the first anatomical description of a member of Helicinidae from northern Peru. The shell is characteristically white, with the first three whorls dark yellow; mantle with irregular dark spots on the dorsal surface, two pairs of odontophore cartilages and a narrow middle one. The male reproductive system consists of a prostate with glandular and collector regions, while the female reproductive system has a small and ovoid seminal receptacle, elongated provaginal sac with irregular projections with its stalk joining mesially, and oviduct aperture in the cloaca, near the mantle border. Records of H. weyrauchi are limited to the seasonally dry tropical forest of the Marañón River, which might indicate that this species is endemic to this ecosystem.

Theta lyronuclea (Clarke, 1959), a North Atlantic deep-water species, is recorded for the first time from the southwestern Atlantic. This constitutes the first record of the genus and the second mention of the family Raphitomidae off Argentina. The samples were collected in the Mar del Plata Submarine Canyon on the Argentine Continental slope on board the R/V Puerto Deseado at 2,934 m depth in September 2013. Photographs of radulae, penises, and details of the ornamentation of the protoconch are provided. Detailed comparison of the specimens collected with the type material and several lots from northern Atlantic localities confirmed the identification.

The diploid number and karyotype of three endemic and highly distributed species from the Qatari shores: Brachidontes variabilis (Krauss, 1848) (Mytilidae), Isognomon nucleus (Lamarck, 1819) (Pteriidae) and Neotrapezium sublaevigatum (Lamarck, 1819) (Trapezidae), are described for the first time. Brachidontes variabilis presented a diploid number of 2n = 30 and the karyotype included 2 metacentric, 6 submetacentric, 3 subtelocentric and 4 telocentric chromosome pairs. Isognomon nucleus had a diploid number 2n = 28 and the karyotype was comprised of 3 metacentric, 4 submetacentric and 7 subtelocentric chromosomal pairs and the karyotype of Neotrapezium sublaevigatum, with 2n = 36, included 5 metacentric, 9 submetacentric, 2 submetacentric/subtelocentric and 2 subtelocentric chromosome pairs. A review of the previously published cytogenetic studies in all three families was also performed, as well as a comparative karyological analysis within those families.

Freshwater mussels have suffered a severe decline during the last century. Accurate description and identification of species have been an arduous and important task for the conservation of this group. Recently, with the promotion of molecular technology, especially mtDNA, many morphological species have been merged. In the genus Lamprotula, L. caveata, L. cornuumlunae and L. leaii are recognized as valid species. The complete mitogenome of. L. cornuumlunae was firstly sequenced in this study. By comparing mitochondrial genomics and phylogenetic analysis, the results showed that mtDNA cannot distinguish between L. caveata and L. cornuumlunae. We hypothesized that the deficiencies of mtDNA in species delimitation was caused by very recent speciation. Time-calibrated multilocus divergence time estimation revealed that L. caveata and L. cornuumlunae recently diverged in the Neogene Pliocene. This study presents the potential problems of relying on mtDNA sequences for delimiting recently diverged species. We emphasis that mtDNA cannot be used solely or dominantly to understand biodiversity. Instead, it is indeed an effective tool, combined with more data, such as shell morphology, reproductive characters and biogeography, to integrate species concepts.

Individual linear growth rates were studied in the freshwater pearl mussel Margaritifera margaritifera from the Vuokinjoki River. Growth deceleration coefficients were shown to vary widely and differ significantly among individuals. The average value of the growth deceleration coefficient for the population is 0.069. The growth of mussels in the Vuokinjoki River is accompanied by three regular biorhythms. These biorhythm periods were roughly constant both through an individual's ontogeny and among mussels. Their average periods were 13.3, 6.4, and 4.0 years. The growth deceleration coefficient a depends on the age of the mussels. We discuss the possibility that the hydrological regime disturbance caused by the Kem hydropower plants' cascade construction could influence the growth rate.

The radula is the anatomical structure used for feeding in most Mollusca species and is one important autapomorphy. Previous studies were focused on the radular teeth and their functional morphology, but their anchorage in the radular membrane and its function have never been examined. Here, we analyse the micro-structure of connecting chitinous fibres and its implication on the radular function in 13 closely related paludomid gastropod species from the so called “ancient lake” Tanganyika. This species flock shows a stunning interspecific diversity in their radular tooth morphology and tooth embedding in the membrane as well. The species studied here feed on organics from different substrates, both soft and solid, and are substrate-specific. Here, the morphological composition of the membrane is described in detail for the first time, it consists of parallel fibres that extend also within the teeth. We also show that morphologies of the anchorage correlated with the specific preferred feeding substrate can hence be identified as functional adaptation.

In recent years, 3D analyses, new indices to describe the complexity of morphological structures and sophisticated machine learning approaches have advanced morphometrical analyses to assist species determination. However, the applicability of these modern approaches to the determination of cryptic species or fossil taxa has rarely been investigated.

In this study, fossil and subfossil specimens of the four modern Dreissena species in the Caspian Sea are used to test the performance of 3D-based morphological approaches for machine learning assisted species identification. Specifically, 3D scans of the shells were used to construct 3D models for calculating “traditional” shell dimensions and “modern” shell complexity parameters. Finally, two machine learning approaches were applied to test the determination performance of shell measurements vs. shell complexity and individual vs. combined shell parameters.

The results show that (i) there is no superior machine learning approach to species determination based on shell characters, (ii) shell complexity parameters are not per se more suitable for species identification than shell dimensions, (iii) a combination of shell parameters increases determination performance and reduces their species dependence and (iv) shell characters alone do not allow precise determination of all Dreissena species studied.

These findings suggest that the most appropriate machine learning approach, the most informative shell characters and the best combination of characters need to be tested individually for different data sets. However, considering that it is difficult even for experts to distinguish Dreissena species based on shell characters, the machine learning assisted classification in the current study has performed comparatively well. Future analyses based on machine learning may therefore help experts to process large sample sizes efficiently and non-specialists to assess species level information with reasonable certainty.

Acroloxus coloradensis is a rare and potentially glacial relict freshwater limpet species endemic to North America. However, despite its remarkable patchy distribution across the continent, only very few genetic data is available for the different populations. Here, we sequenced two standard barcoding markers for individuals from five populations to shed some light on the genetic population structure of this species. Overall, our genetic analyses revealed low genetic variation and identified three and two haplotypes for COI and 16S rRNA, respectively. The three Rocky Mountain populations differed only slightly for COI and shared the same haplotype for 16S rRNA. For both markers, no genetic variation was detected within the two populations sampled in Québec. The present genetic data suggest that A. coloradensis is indeed a relict species and that the distribution of this species was strongly affected by the last glacial retreat in North America.

Two specimens of the mimic octopus Thaumoctopus mimicus were documented for the first time in the Arabian Sea during September 2018 off southern Kerala, India, from 15 m depth. The specimens had dorsal mantle lengths (DML) of 44 and 48 mm. Description and morphological measurements of the specimens are provided. The identity of the specimens was genetically supported by using cytochrome C oxidase I gene sequencing. This finding represents the first record of the species in the Arabian Sea, which signifies an extension of its known geographic distribution range.

Land snails of the family Achatinidae, subfamilies Subulininae and Opeatinae, are commonly reported as alien species in European greenhouses, where they often reach high densities. These introduced species usually have tropical cosmopolitan distributions. Four of them (Opeas hannense, Allopeas clavulinum, Subulina octona, and S. striatella) are commonly reported and illustrated from greenhouses across Europe. A fifth species, Allopeas gracile, has also been reported from Europe, though from a few records only. In this paper, we report on a European colony of a sixth species, Paropeas achatinaceum, that was discovered in Austria in 2016. We provide photographic documentation for these six species with critical characters to distinguish them. In the past, at least five other alien nominal subulinine species have been reported from greenhouses in Europe. These are briefly discussed along with nomenclatural notes.

Species identification on the basis of specific mass profiles of peptides and small proteins – proteomic fingerprinting – is becoming increasingly popular among zoologists. While the method has been successfully applied to various groups of invertebrates, its applicability to gastropod species has not yet been tested. Here we use the cryptic brackish water mudsnail genus Ecrobia as a model taxon to assess the discriminative power of this approach in comparison to DNA-based approaches. Our pilot study shows that proteomic fingerprinting discriminates most species of Ecrobia well and that the discriminatory performance is similar to that of molecular phylogenetics based on mitochondrial genes. Thus, Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight Mass Spectrometry (MALDI-TOF MS) may serve as a relatively inexpensive tool for an efficient identification of gastropod species.

In order to establish management measures for a new resource, the size at first maturity should be studied. This measurement is a powerful tool in enabling the sustainable exploitation of marine benthic resources. Patagonian marine gastropods are captured as complementary catches during scallop fisheries. Studies related to the size at first maturity were performed for edible marine gastropods in northern Patagonia and have been used for the creation of the first regulation of gastropod catches made by the Secretary of Fisheries of Chubut Province. The minimum capture size of some of the species included in this regulation was established from preliminary studies but needed histological confirmation. The present study aims to provide accurate information on the size at maturity by an assessment that includes first gonadal maturity and population size/weight data of Buccinanops deformis and Trophon geversianus, two edible species of marine gastropods with high abundance along the Patagonian Atlantic coast and elevated nutritional values in their edible tissues. By histological methods, females of B. deformis reach maturity at 2.8 cm and males at 1.95 cm. While by an alternative histological method (inflexion point method), females reach maturity at 2.76 cm and males at 2.1 cm. For T. geversianus, females reach maturity at 3 cm (inflexion point = 2.38 cm) and males at 1.65 cm (inflexion point = 2.01 cm). The maturity assessment of B. deformis and T. geversianus revealed that males reach maturity at a smaller size than females, probably due to the fact that females require a more gradual process in maturation with a greater reproductive investment. The size at first sexual maturity provides valuable information for establishing the minimum catchable size. Therefore, we estimate a minimum size limit for B. deformis of 3.6 cm and 3.5 cm for T. geversianus and suggest that fishery measurements for these species should be established by performing a particular maturity assessment in each fishery zone.