ABSTRACT Pseudomulleria dalyi (E.A. Smith, 1898), an endemic and endangered freshwater bivalve of the Western Ghats, has long posed a taxonomic challenge because its larval morphology has remained unknown. Traditionally placed within the family Etheriidae based on its cemented shell morphology, its phylogenetic position has been debated, with molecular evidence instead suggesting affinities with Unionidae. In this study, we provide the first description of the reproductive biology and larval morphology of P. dalyi. Field surveys in the Tunga and Bhadra rivers in India revealed gravid females containing eggs, immature glochidia and mature glochidia in all four demibranchs. Scanning electron microscopy showed that the glochidia are hookless and D-shaped, consistent with the hypothesized placement of P. dalyi in the Unionidae. These findings provide important new evidence for the evolutionary relationships and reproductive biology of this species and underscore the diagnostic value of larval morphology in freshwater mussel systematics.
Terrestrial gastropods fulfil pivotal ecological roles, yet numerous species have emerged as high-impact invaders, producing significant consequences for biodiversity, agriculture and human health. While their ecological effects are well documented, the behavioural strategies employed by these invasive species remain comparatively underexplored. Given their limited sensory modalities, chemical communication mediated through slime is central to gastropod behavioural ecology. This study investigated open-area exploratory behaviour in the invasive giant African land snail (Lissachatina fulica) and the native horntail snail (Tanychlamys indica), both collected from sympatric habitats and observed under controlled laboratory conditions. Juvenile and adult individuals of each species were exposed to homospecific and heterospecific slime cues. Results revealed contrasting interspecific responses, such as T. indica, which exhibited suppressed exploration in the presence of heterospecific slime across life stages, suggesting potential spatial displacement and reduced activity. In contrast, adult L. fulica showed enhanced exploratory activity upon encountering heterospecific slime, consistent with a facilitative interaction, whereas juveniles showed minimal sensitivity to both homospecific and heterospecific chemical cues. Asymmetric responses to slime-borne chemical cues between native and invasive gastropods may drive competitive exclusion of T. indica, cascading through food webs to disrupt predator-prey dynamics and threaten ecosystem functioning, while heightened exploration by invasive L. fulica in response to native cues highlights opportunities for synthetic slime-mimicking decoys to divert snails from crops or concentrate them in baited traps. Ultimately, this chemical dialogue in slime not only guides gastropod behaviour but may silently script the outcome of biological invasions.
Cerastoderma glaucum is a euryhaline bivalve mollusc that inhabits estuarine and shallow coastal water ecosystems across Europe, North Africa, the Mediterranean, the Black Sea and the Sea of Azov. Although it is ecologically significant and widely distributed, comparative studies of its morphological and reproductive traits at the population level in response to environmental stressors remain limited. This study examines the morphometric, allometric and sex-related variability of C. glaucum populations from two ecologically contrasting sites in the Azov-Black Sea region. Shell dimensions, soft tissue and shell weights, and sex structure were analysed. Morphometric indexes and allometric relationships were assessed using statistical and multivariate methods. Individuals from Kamysh-Burunskaya Bay were significantly larger in all linear and weight parameters compared to individuals from Russkaya Bay, whereas shell shape indices did not differ significantly. Allometric analysis revealed contrasting growth patterns for C. glaucum: In Kamysh-Burunskaya Bay, shell height and width increased more slowly than shell length, and soft tissue weight showed negative allometry; in Russkaya Bay, all linear shell dimensions showed positive allometry, and soft tissue weight increased strongly with shell length. Shell weight showed negative allometry in both populations. An analysis of covariance confirmed significant between-population differences in shell dimension scaling and tissue weight scaling but not in shell weight scaling. Principal component analysis revealed clear morphological separation between populations. Analysis of the sex ratio revealed no deviations from 1:1 in Kamysh-Burunskaya Bay, while in Russkaya Bay there was a significant bias towards females (70%, P = 0.03). The results highlight the phenotypic plasticity of C. glaucum and its sensitivity to local environmental conditions. The combination of morphological and reproductive indicators provides insight into the strategies of populations to adapt to various environmental stresses, which is important for monitoring benthic communities in transitional marine systems.
