Extending over warmer environments in the Brazilian waters, the exotic vermetid Eualetes tulipa was first recorded from Ceará State (3°S) in 2005. In 2009, it was reported in cold-water environments in Rio de Janeiro State (22°S). Seven years later, E. tulipa was recorded from Rio Grande do Norte State (6°S) on rocky pools in sandstone reefs. In the present study, E. tulipa is for the first time recorded from Bahia State (12°S), associated with a biofouling community in the Todos-os-Santos Bay, co-occurring with exotic dendrophylliid corals (Tubastraea). The vermetid community recorded from Bahia State shows a great diversity of epibionts, mostly bivalves, cirripeds and sponges. The co-occurrence of Eualetes and Tubastraea corals must be monitored, once these exotic species are co-occurring in a protected environmental area, bringing concern on possible impacts on native benthic fauna.

The Didymozoidae (Trematoda: Hemiuroidea) is among the most speciose trematode families, known from a wide range of marine teleost fishes. Despite their richness, however, didymozoid life cycles are unusually poorly known; only two first intermediate hosts are known, a marine bivalve (Anadara trapezia) and a pelagic gastropod (Firoloida desmarestia). This study uses multi-locus molecular sequence data to identify a novel first intermediate host for the family, a sessile gastropod of the genus Thylacodes Guettard (Vermetidae). The didymozoid infection is not identified to species but, based on molecular phylogenetic analyses, it is close to Saccularina magnacetabula Louvard et al., 2022, which uses a bivalve as a first intermediate host. The distribution of known first intermediate hosts of didymozoids (a bivalve, a holoplanktonic gastropod and a sessile gastropod that feeds with the use of mucus nets) suggests that first intermediate host use within the Didymozoidae has been opportunistically driven by the trophic ecology of potential mollusc hosts and has involved significant host-switching events.

The superfamily Pronocephaloidea Looss, 1899 comprises digeneans occurring in the gut and respiratory organs of fishes, turtles, marine iguanas, birds and mammals. Although many life cycles are known for species of the Notocotylidae Lühe, 1909 maturing in birds and mammals, relatively few are known for the remaining pronocephaloid lineages. We report the cercariae of five pronocephaloid species from marine gastropods of the Queensland coast, Australia. From Lizard Island, northern Great Barrier Reef, we report three cercariae, two from Rhinoclavis vertagus (Cerithiidae) and one from Nassarius coronatus (Nassariidae). From Moreton Bay, southern Queensland, an additional two cercariae are reported from two genotypes of the gastropod worm shell Thylacodes sp. (Vermetidae). Phylogenetic analysis using 28S rRNA gene sequences shows all five species are nested within the Pronocephaloidea, but not matching or particularly close to any previously sequenced taxon. In combination, phylogenetic and ecological evidence suggests that most of these species will prove to be pronocephalids parasitic in marine turtles. The Vermetidae is a new host family for the Pronocephaloidea.

We examined the density and reproductive characteristics of the Israeli population of the cryptic species complex Dendropoma petraeum—a Mediterranean endemic reef-building gastropod. The population is gonochoristic, with a peak of gonad activity from October–November to May–June. We present here for the first time histological evidence of its reproductive cycles, hermaphroditism and gonadal parasitic infestation. The characteristics studied (gonad activity period, number of egg capsules per female, capsule size and number of eggs/embryos per capsule) were markedly different from those reported for the D. petraeum-complex population in south-east Spain. Our findings on the population's reproductive characteristics provide new information on the differences between the Mediterranean populations of D. petraeum-complex.

The population density, annual gametogenic cycle, and size at sexual maturity of two vermetid species, Eualetes tulipa (invasive) and Dendropoma corrodens was studied in the southern Caribbean at the Planta Centro power plant intake channel and at Punta Mayorquina, Morrocoy National Park, respectively. Minimal size of mature females of E. tulipa and D. corrodens was 5.0 and 0.7 cm in body length respectively. The gonad represented between 44 to 47% of total body length, while it represented between 15 to 18% of total body volume (for both males and females). Gonad volume was significantly related to total body volume. A significant quadratic relationship between the number of capsules and female body volume was obtained for E. tulipa, indicating that females measuring 6–10 cm in body length are those that have the highest number of egg capsules. Females larger than 11 cm have a lower fecundity in terms of brooded capsules. Gonad sections of males and females of both species showed that several gametogenesis stages are simultaneous within the same individual. In the female, germ cells, oogoniums and primary oocytes with yolk granules were observed simultaneously. In the male, the spermatogonium, primary and secondary spermatocytes, spermatids and sperm cells were also observed within one gonad. The same pattern was observed throughout the year, showing no maturation/resting period or annual cycle. The area covered by D. corrodens was about 700 m2 with a mean density of 13,000 ind/m2. The area covered by the invasive E. tulipa was at least about 1000 m2, with a density of 27,000 to 29,000 ind/m2 in the first 3 m of depth. A follow up of the E. tulipa population showed that its density is increasing in time and has doubled in 20 years. This population increment could be related to an increase in organic suspended matter as evidenced in the region.