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The population structure and reproductive biology of the semiterrestrial crab Sesarma rectum were studied in an impacted tropical mangrove in northeast Brazil. Crabs were collected monthly during spring low-tide periods from October 2009 through September 2010. A catch-per-unit-effort (CPUE) technique was used to sample the crab population, using two-hour sampling periods by two people. A total of 492 crabs was obtained, of which 262 were males, 151 non-ovigerous females, and 79 ovigerous females. Males were significantly larger than females, whether non-ovigerous or ovigerous. There was no significant difference between mean size of the ovigerous and non-ovigerous females. The population showed a unimodal size-frequency distribution, with a normal distribution for males and non-normal for females. The overall sex ratio (1 : 0.87) did not differ significantly from the expected 1 : 1 proportion. Ovigerous females were found during the entire period, except in March and August 2010. The mean number of eggs was 14 975 ± 5689. The highest number of eggs was recorded for the 29 to 31 mm age group. A regression analysis showed that the number of eggs increased linearly with carapace width () and abdomen width (). Comparisons among populations will help to evaluate the differences among them, as well as to understand the environmental and biological constraints that are shaping them. [ABSTRACT FROM AUTHOR]

Melanoides tuberculatus is an Afro-Asiatic thiarid, common in freshwater environments, now present in a wide portion of the tropical and subtropical regions of the New World. The present study had as its objective to register the occurrence of M. tuberculatus in the area of mangrove of the estuary of the Ceará River, verifying its density and the salinity which the specimens were submitted to verify its euryhalinity. Specimens of M. tuberculatus were collected in mangrove areas of the estuary of the Ceará River, located on the boundary of Caucaia and Fortaleza. Some specimens collected by hand in February 2006 were kept in an aquarium for a month. The abundance of M. tuberculatus in the studied areas varied from 0.76–10.22 individual/cm2. The salinity of the areas varied from 0–30 in the studied months. The presence of M. tuberculatus in these mangrove areas, whose salinity reached a peak of 30, and their survival in the laboratory, under a salinity of up to 35, prove the adaptation of this limnetic gastropod to euryhalinity. [ABSTRACT FROM PUBLISHER]

Encapsulation of embryos in marine gastropods affords protection for the developing young, whether or not parental care takes place. The capsule wall is laminated and its dimensions change during development. Dissolution of the capsule wall releases dissolved organic matter (DOM) into the intracapsular fluid, providing a nutritional source for the embryo. The capsule wall of Acanthina monodon is composed of three layers, a thin outer layer with projections to the exterior, a thicker intermediate layer containing vacuoles and a thin inner layer that gives rise to the hatching plug. During embryonic development the capsule wall lost 27.2% of its initial mass owing to a pronounced thinning of the outer layer, especially of the projections. The organic fraction in the capsule wall (>85% of total mass) decreased by 23.3%, mostly due to the loss of 52.8% of the protein originally present. The internal layer of the capsule wall became 35.2% thinner during embryonic development, and in capsules containing embryos in the prehatching stage the surface area of a section through the plug was reduced to 2% of its original value. Total protein concentration in the intracapsular fluid decreased by 54% during embryonic development. The dry weight of the encapsulated juveniles immediately before hatching was 96% greater than that of the eggs from which they developed. Total protein concentration increased by 148% between the egg and the advanced veliger stages, then decreased in the prehatching juvenile, presumably as a result of the energy cost of metamorphosis, which occurs within the capsule before the juveniles are released. During development, material was lost from the exterior surface of the outer layer of the capsule wall. In contrast, the inner layer partially dissolved and disintegrated into the intracapsular fluid, providing the developing embryos with a secondary source of nutrition, mainly protein, during the later stages of encapsulation, when the material from the nurse eggs was exhausted. [ABSTRACT FROM AUTHOR]

Many invertebrates enclose their embryos within egg capsules, from which the offspring hatch. In marine gastropods that brood their egg capsules, hatching could involve radular activity by the mother or by unhatched stages, increased osmotic concentration of the intracapsular fluid, or production of hatching enzymes. The present research sought to determine whether mechanical action by the brooding female or by the encapsulated embryos was involved in the hatching for two sympatric and closely related species of calyptraeid: Crepipatella dilatata, which exhibits direct development without free-living larvae, and Crepipatella peruviana, which releases free-living veliger larvae. We also considered the role that enzymatic action or osmotic changes in the intracapsular fluid might play in hatching. Using scanning electron micrograph analyses, we found no evidence that the well-developed, pre-hatching juvenile radula of C. dilatata played any role in the hatching process and that the radula of C. peruviana did not even develop until long after hatching; so there was no evidence of radular activity involved in the hatching of either species. For C. peruviana, the intracapsular fluid osmolality was always higher than that of the surrounding seawater, suggesting that there is a strong natural water inflow during development. Moreover, when egg capsules of C. peruviana were exposed to lower ambient salinities, the substantial entry of water correlated well with high percentages of hatching, particularly for egg capsules containing advanced veligers, suggesting that an osmotic mechanism may be involved in the hatching process of this species. In contrast, hatching in C. dilatata appeared to be enzymatically mediated. [ABSTRACT FROM AUTHOR]