Histological Study on the Reversal Gonadal Activity in the Mussel Lithophaga truncata (Gray, 1843) during Testicular Phagocytosis (Pelecypoda - Mytilidae)

The histological observations of the gonad in the mussel Lithophaga truncata (Gray, 1843), inhabiting the Arabian Gulf in Saudi Arabia, indicated that there was only one gonadal cycle in the year. During November - February the gonadal follicles were in a quiescent state. Follicles were few in number and scattered throughout the vesicular connective tissue. In females oogonia and previtellogenic oocytes predpminated the ovary. In males the follicles were small and scattered throughout the connective tissue in the same way as females. During April - July previtellogenic oocytes began to undergo growth phase and extending towards the center of the follicles. In males spermatogenesis became more apparent and proceeded at a faster rate. The gonadal follicles ramified rapidly, and the development of gametes of both sexes was very fast. In females the vitellogenic oocytes showed prominent development. During August - October both sexes had ripe gametes. In males, the central portion of the follicles was empty because of the recent discharge of large quantities of ripe gametes. At the end of this step resorption of the gonads proceeded very rapidly and emptied follicles began to acquire an elongated form. It was found that during the process of resorption of the testicular follicles of 15 males out of 50, increased number of undifferentiated residual cells appeared inside the follicles which seems to be phagocytic in function. Many oogonia and previtellogenic oocytes appeared inside the vesicular connective tissue among the testicular follicles.