The androgenic gland of Penaeus vannamei vannamei and P. stylirostris (open thelycum shrimps) is described. The gland is a cellular strand that appears associated to the vas deferens from the proximal region of the terminal ampula; however, a more detailed study is required to confirm its secretory nature. The spermatogenesis in P. stylirostris and Trachypenaeus byrdi (close thelycum) is synchronized, and the ultrastructural morphology of spermatogenic stages observed is different from that described for Sicyonia ingentis. Penaeus stylirostris spermatids gradually develop the spine in the descendent medial vas deferens, and T. byrdi spermatids seem to complete maturation in the female telica after copulation. Ultrastructural observations of T. byrdi oogenesis indicated that 5-10 um oocytes are in previtellogenesis, separated by a thin membrane. At the beginning of primary vitellogenesis, oocytes measure 6-10 um and follicle cells are not surrounding them. Oocytes at secundary vitellogenesis, show a thin layer of follicle cells, a vitelline envelope, specializations like cortical cripts, ring vesicles cisterns and microtubules network.
