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This study aims to analyze the functional anatomy of the male reproductive system in Neocaridina davidi, a very popular ornamental species of caridean shrimp. Mature males were cold‐anaesthetized and their reproductive systems were dissected for histological and histochemical analysis, while the spermatozoa and spermatophore wall ultrastructure were analyzed under transmission electron microscopy. The male reproductive system consisted of two coiled testes, which were continuous with the vasa deferentia. Testes were positioned on the dorsal side of the cephalothorax above the hepatopancreas, and comprised seminiferous tubules where spermatogenesis occurred. Each vas deferens (VD) was a long tube dorsolaterally positioned with respect to the hepatopancreas, and increased in diameter at the distal end. Three regions could be recognized in the VD: proximal, middle, and distal. The proximal region had a cylindrical epithelium with secretory cells. The middle region (or typhlosole) had a dorsal fold (or typhlosole) with a thick columnar epithelium and high secretory activity. The spermatophore was a continuous cord with three acellular layers, which were mainly characterized by the presence of neutral glycoconjugates and proteins. The sperm morphology was distinct from the inverted cup‐shaped spermatozoa observed in the majority of caridean shrimps. The spermatozoa in specimens of N. davidi were spherical in shape, with a cross‐striated, single, short spike, and arranged in clusters of three or four sperm cells. The composition of the spermatophore, and the arrangement and form of the spermatozoa, seem to be unique in comparison to other species of Caridea.

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This study describes the mating behavior of Hypoconcha parasitica under laboratory conditions highlighting the spermathecal morphology and focusing on the seminal fluid storage and release of spermatozoa. The pairs were kept in aquaria where the mating behavior was recorded and described. The spermathecae of the female were analyzed using scanning electron microscopy, X‐ray micro‐CT, histology, and histochemistry. No pre‐ or post‐copulatory mate guarding was observed in H. parasitica. The sperm transfer occurred with each pair maintaining the protection shield (bivalve shell) on their dorsum. The pair of spermathecae is covered exclusively by the cuticle, following the Podotremata pattern. Many muscle fiber bundles are attached to the cuticular wall facing toward the cephalothorax cavity, especially covering the lateral and slightly dorso‐anterior region toward the apodeme of Sternite 7. The spermathecal organization indicates that the process of sperm release during fertilization occurs through muscular action exerted by the female on the wall of the chamber. Thus, the musculature distribution in Hypoconchinae distinguishes them from described for other Podotremata such as Homolidae, which shows the musculature associated with the spermathecae aperture. Like the Homolidae, the first pleopod in H. parasitica seems to take part in the transfer/ movement of spermatozoa and oocytes between the sternum and abdomen, which forms a temporary chamber where fertilization occurs. In conclusion, the spermathecal morphology and associated structures bring new insights to the mechanisms involved in the sperm storage and fertilization of primitive crabs and how the Dromiidae spermatheca perform a new pattern among the poorly studied Podotremata.

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The ovarian development of Callinectes ornatus and Arenaeus cribrarius was described using histochemistry and ultrastructure analyses. Both species shows six stages of ovary maturation: juvenile (JUV), rudimentary (RUD), developing (DEV), intermediary (INT), mature (MAT) and spent (OV). The JUV and RUD stages showed similar histological and histochemical characteristics, in which the oocytes cytoplasm is basophilic and glycoproteic yolk nucleus is observed. The cytoplasm shows small acidophilic portions, stained for protein and reactive to PAS, which correspond to the dilated cisternae of the rough endoplasmic reticulum (RER) in ultrastructure. The exogenous phase begins at the DEV stage, with the fusion between pinocytic vesicles and vesicles of immature yolk, forming the mature yolk granules. At the INT stage, the formation of the chorion begins and the mature yolk granules increase in size and number, and the lipid and glycogen reserves are expanded, while the ER diminishes. In MAT, the oocytes are completely formed. Additionally, the cytoplasm is filled with mature yolk granules, lipids droplets and glycogen. There are no significant variations between the gonadosomatic and hepatosomatic indices, which allow us to infer the transfer of reserves from the hepatopancreas to the development of the female reproductive system in the portunids studied.