Internal anatomy and ultrastructure of the male reproductive organization of the Sesarmid crab Muradium tetragonum (1798)—(Decapoda: Brachyura)

Sesarmid crab, Muradium tetragonum, considered a key detritus consumer plays a significant role in the nutrient cycling and energy flow in most of the mangrove environments. Morphological and ultrastructural organization of the M. tetragonum male reproductive system are characterized through transmission electron microscopic studies. Adult males (3.2–4.2 cm) with dark violet carapace and white-tipped cheliped were procured alongside the coastal areas of Tanjavur district, Tamil Nadu, India. The morphological analysis highlights the male gonads to be bilaterally symmetrical and anterolaterally located inside the cephalothorax. A pair of elongated testes lying attached to the hypodermis of the carapace leads to a long highly coiled vas deferens categorized into three distinct regions (Proximal vas deferens, Middle vas deferens and distal vas deferens) structurally and functionally with Posterior vas deferens receiving sac-like accessory glands. It gets followed by an ejaculatory duct and ends with the penile papillae at the coxae's base of the fifth peripod. Structural modifications were observed in the ultrastructure of vas deferens envisage (considering) its functional role in storing spermatophores, active absorption and assisting the secretory activity. Spermatophores, witnessed as spherical bodies are bounded by a dense double wall. Aflagellate, immotile and spherical spermatozoa that measuring 3.6 μm in diameter encompasses a complex acrosome cupped by a nucleus. Moreover, perforatorium and the extending nuclear arms with chromatin, as displayed in the experimental organism M. tetragonum, are in synergy with that of certain brachyurans as specified in the study. Hence, the current study assessing the morphology and ultrastructure parameters of the male gonads could be useful in understanding the physiology of sexual maturation, annual cyclic changes, tracing the phylogenetic relationship among species and enhancing the brood-stock management.