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The gonad morphology and gametogenesis of three peltospirid gastropods (Nodopelta heminoda, N. subnoda and Peltospira operculata) from hydrothermal vents in the East Pacific Rise were analysed using histological techniques. Samples were collected on different hydrothermal structures from three chemically distinct sites in vent fields along the north East Pacific Rise (13°N) to assess spatial variation in oocyte size–frequency distributions. The three species revealed the same gonad morphology. The ovary, which occupies a large part of the body, is confined to the dorsal area of the visceral mass and is located between the dorsal gill lamellae and the digestive gland that appear progressively from the posterior part. The oogonia develop into previtellogenic oocytes, and when they grow to a size of 50–70 µm, vitellogenesis begins. Maximal egg size ranges between 129 µm for P. operculata and 150 µm for N. heminoda. The presence of oocytes at all stages of development, in all females, suggested a continuous gametogenesis within those species. Continuous reproduction appears to be a common trait in vent gastropods and may be adaptive in relation to constant energy supply and the ephemeral and unstable vent environment. Percentage of vitellogenic oocytes (i.e. gametogenic maturity) was independent of shell length. The slight variability observed between gametogenetic maturity of females from different localities is likely due to random individual variations in reproductive patterns rather than variation in environmental conditions or food availability. [ABSTRACT FROM PUBLISHER]

The recovery of populations and their ability to recolonise a disturbed habitat is mainly dependent on their reproductive biology (e.g., fecundity, frequency of reproduction, and time to maturity) and recruitment success. To assess recolonisation processes and connectivity of vent communities, and infer their resilience to natural and anthropogenic disturbances, we studied the life-history traits of two dominant species of vent gastropods from the northern Mid-Atlantic Ridge: Protolira valvatoides and Pseudorimula midatlantica. Gonad morphology, gametogenesis, and reproductive outputs related to shell length were described using histological analyses, and population structure was assessed from individuals' size–frequency distributions. Samples were collected at different locations of the Montségur and Eiffel Tower edifices (Lucky Strike vent field) in April 2015, July 2017, and August 2018 to inform on spatial and temporal variations of their reproductive outputs and demography. All stages of oocyte development were found in the gonads of both species, suggesting a continuous gametogenesis and asynchronous reproduction. However, the two species showed contrasting reproductive strategies. Indeed, while P. midatlantica is gonochoric with a fecundity of up to 327 mature oocytes, P. valvatoides is hermaphrodite with an extremely low fecundity including a maximum of eight vitellogenic oocytes. Maximum oocyte size was 176 µm for P. midatlantica and 272 µm for P. valvatoides. We infer from previous knowledge and our results that both species exhibit a lecithotrophic development of larvae. There was no evidence of temporal variability of reproductive traits, but environmental conditions seem to affect gametogenetic maturity and oocyte size of P. midatlantica limpets. Variations in population structure at the edifice scale suggest habitat selection of individuals related to biotic and abiotic factors. [ABSTRACT FROM AUTHOR]