Probing the architecture of testis and morphology of male germinal cells in the mud crab with the atomic force microscopy

The architecture of testicular lobules, morphology of spermatozoa, and spermatophore in the mud crab, Scylla serrata, are described for the first time employing atomic force microscopy (AFM). A fast and simple squash preparation protocol was followed using crustacean physiological saline without distorting the natural structure. Observations provided new insight into the arrangement of lobules and morphology of testicular assembly. It consists of a close network of lobules of different sizes in a radial manner on radially branching basal tubules. Budding of new lobules is another distinguishable feature noted in the network of testicular organization. A thin membranous envelope of the lobule with undulating processes offered indirect evidence on the possible storage of sperm cells within the lumen of the lobule. Spermatozoa of S. serrata were of different shapes and sizes, and, depending on the maturational status, they displayed changes in the acrosome vesicle with a significant amount of cytoplasm. Vertical constrictions found in the testicular lobules suggest propulsive extrusion of spermatophoric masses into the central lumen. These observations necessitate further study using AFM and involving molecular probes to elucidate the polymorphic nature of male germinal cells, mechanisms of spermatophore formation, and the phylogenetic relationship among crustaceans in general.