Internal anatomy and ultrastructure of the male reproductive system of the spider crab Maja brachydactyla (Decapoda: Brachyura).

The morphology and function of the male reproductive system in the spider crab Maja brachydactyla, an important commercial species, is described using light and electron microscopy. The reproductive system follows the pattern found among brachyuran with several peculiarities. The testis, known as tubular testis, consists of a single, highly coiled seminiferous tubule divided all along by an inner epithelium into germinal, transformation, and evacuation zones, each playing a different role during spermatogenesis. The vas deferens (VD) presents diverticula increasing in number and size towards the median VD, where spermatophores are stored. The inner monostratified epithelium exocytoses the materials involved in the spermatophore wall formation (named substance I and II) and spermatophore storage in the anterior and median VD, respectively. A large accessory gland is attached to the posterior VD, and its secretions are released as granules in apocrine secretion, and stored in the lumen of the diverticula as seminal fluids. A striated musculature may contribute to the formation and movement of spermatophores and seminal fluids along the VD. The ejaculatory duct (ED) shows a multilayered musculature and a nonsecretory pseudostratified epithelium, and extrudes the reproductive products towards the gonopores. A tissue attached to the ED is identified as the androgenic gland.