Developmental morphology of claspers and clasper-glands during maturation in Potamotrygon wallacei (Chondrichthyes: Potamotrygoninae).

The claspers are the copulatory organs in male elasmobranchs, responsible for directing the semen into the female cloaca (C). However, the microscopic morphology of the claspers remains poorly understood. This study describes the morphology of the claspers and clasper glands (CGs) of cururu stingray (Potamotrygon wallacei) at different maturational stages, including neonates, juveniles, and adult active males. These secondary sexual organs were analyzed anatomically and processed using standard histological and histochemical staining techniques. The claspers of P. wallacei have a tubular shape and a brown coloration with light spots, intensified in juveniles and active males. Claspers are flexible in neonates, show an increased rigidity in juveniles, and are fully rigid in adults. Gradual rigidity of the claspers results from mesenchyme (ME) replacement by cartilage followed by mineralization. The claspers are lined by an epidermis (EP) with mucous cells (MC) secreting neutral and acid carboxylate mucosubstances; spermatic groove (SG) with cells exhibiting neutral mucosubstances; vascularized connective tissue and musculature associated with nerve bundles. Such tissue characteristics can assist in penetration, protection, rotational movements, and opening of the claspers during copulation. The CG is recognizable in neonates and becomes progressively more structured through ontogeny, reaching full differentiation in adults. The CG is delimited by two external muscular tunics, with secretory units (SU) formed by a simple columnar epithelium, demonstrating a holocrine secretion with neutral and acid carboxylate mucosubstances, more intense in adults. This secretion can assist in sperm capacitation, nutrition, and motility. These results confirm that secondary sexual organs undergo morphophysiological changes during sexual maturation in P. wallacei.