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ABSTRACTWe investigate the onset of morphological sexual maturity, sexual dimorphism and relative growth of the freshwater crab Fredius ibiapaba. We collected the specimens bimonthly between August 2017 and June 2018. We measured the crabs to obtain the following morphometric variables: carapace width (CW); pleon width (PLW); propodus length (PL); propodus height (PH) and propodus width (PW). A total of 175 specimens of F. ibiapabawere analysed. The onset of morphological sexual maturity was estimated at 31.7 mm for males, and at 35.2 mm for females. We observed sexual size dimorphism in CL and PLW, with females larger than males. Positive allometry of cheliped variables was observed in juvenile and adult males, while females showed positive allometry of PLW in juvenile and adult. Finally, the growth of the variables was different between adults and juveniles in both sexes. The ecological information obtained in our study is unprecedented for the genus Fredius. The sexual size dimorphism with females larger than males, probably resulting from their reproductive biology. Additionally, the energy expenditure in cheliped growth in males, may be associated with success during agonistic disputes and the use of these structures to position females during copulation, since they are larger in body size.

Aplysia dactylomela is a large marine opisthobranch gastropod, which inhabits shallow tropical shoreline regions, eats red and green algae, and releases a purple ink when disturbed. Many functions have been proposed for this secretion and although there is no consensus on this, some of its constituents are believed to be derived from the red algal diet, it may provide the snail with a substantial survival advantage. A. californica only produces ink when it ingests red seaweeds. In some locations of the Northeastern Coast of Brazil, A. dactylomela is seen feeding only on green seaweeds, and yet it releases the ink. The aim of this work is to investigate this contradiction by studying the feeding habits of A. dactylomela and assessing the relationship between the algal diet and the purple ink. Feeding habits were investigated by field observation and by analysis of gut contents. Purple ink production was monitored by histologic analysis of the ink gland from sea hares kept in water tanks, fed with either red or green seaweeds. Composition and protein profile of the purple ink also were studied. Homologies between seaweed components and the purple ink were sought for by immunodiffusion techniques. Our findings are that the sea hare A. dactylomela, likewise other Aplysia species, needs to consume red seaweeds to be able to secrete the purple ink. The proteins of the ink seem to be synthesized by the sea hare itself and are not obtained directly from the diet, as is the case for the ink pigments. [ABSTRACT FROM AUTHOR]