The Atlantic blue crab (Callinectes sapidus Rathbun, 1896) is a euryhaline and eurythermal species native to the Atlantic coasts of the Americas. Although its widespread distribution across the Mediterranean basin is well documented, information on its reproductive patterns remains limited. This study focused on the combination of both macroscopic and histologic characterization of ovarian developmental stages in female blue crabs along the north-central Italian Adriatic coast, within the spawning period. Samples were collected off the coast of Ancona, in collaboration with local fishermen, between September and November 2023. For each specimen, sex and biometric parameters were recorded to determine the sex ratio, while size distribution and gonadosomatic index (GSI) were calculated for female specimens. Ovary samples and eggs sponge were collected to determine the ovarian developmental stage and fecundity respectively. Results showed females as the dominant sex throughout the sampling period, with males being extremely rare. The collapse of female catches in early November, alongside the consistent presence of ovigerous females and the strong female-biased sex ratio, identified this area as a spawning ground. These findings align with reproductive patterns observed in the species' native range and other Mediterranean areas. Moreover, GSI values and fecundity indexes associated with macroscopic and histological examination of ovarian stages suggested that the end of the reproductive season corresponded to mid-November.

The barrel jellyfish (Rhizostoma pulmo), like other cnidarians, shows cnidocytes containing cnidae, responsible for the jellyfish’s stinging properties. The sting of R. pulmo can cause contact dermatitis or urticaria and even systemic symptoms. Recent studies have identified stinging-cell structures in the mucous secretion released in the water column by Cassiopea xamachana, belonging to the same order as R. pulmo. The present paper verifies the release of stinging-cell structures in the water by R. pulmo and reports the case of two 17-year-old adolescents (one male and one female) who were affected by epidermal rashes consistent with the irritating sensations of stinging water. The reaction happened twice in the Ionian Sea; the patients were in proximity to R. pulmo but, on both occasions, there had been absolutely no direct contact with the jellyfish’s tentacles. To test the hypothesis of stinging water caused by R. pulmo, samples of sea water and mucous harvested in close proximity to a living jellyfish were taken and analyzed under a microscope at different magnifications. The microscopic analysis showed the presence of free and aggregated nematocysts in both the samples of water and mucous. It is likely that the free and aggregated nematocysts observed were discharged in the water by the jellyfish and were dispersed by water currents that led them to come into contact with the patients’ skin. At present, it is not known what predisposes humans to the perception of stinging water, and it is reasonable to affirm that caution should be advised for people with an allergic history when entering the water in the presence of jellyfish. Further investigations are required to better understand both the pathophysiological pathways underlying the stinging water phenomenon and the minimum concentration of urticating elements that is able to trigger the onset of stinging water.