Fine structure of the gonadal tissue of the horned octopod Eledone cirrhosa (Lamarck, 1798) (Mollusca – Octopoda) during sexual maturity

Abstract

Abstract The horned octopod Eledone cirrhosa, a medium-sized species found in Arabian Gulf off Saudi Arabia, was collected monthly from the Arabian Gulf off Dammam city during January to December 2022. Samples were dissected and prepared for examination using transmission electron microscopy. During genital maturation, seminiferous tubules are established in the testis, with active spermatogonia dividing. Spermatocytes 1 are observed in the tubule, followed by an increase in spermatogonia and spermatocytes in August. Spermiogenesis begins, with spherical spermatids evolving into elongated spermatids. In September, active spermatogonia, meiotic divisions, and increased spermiogenesis continue. Spermatozoa appear in Needham's pouch, indicating sexual maturity. The ovary undergoes various stages of development, with oocytes at stage I in June and July, followed by stage II in October and November. In stage III, follicular cords invade the oocyte's cytoplasm, forming numerous lipid inclusions and protein granules. The cytoplasm contains cisternae of endoplasmic reticulum and a poorly developed Golgi apparatus. Stage IV occurs in November, characterized by the maximum development of follicular cords and the beginning of vitellogenesis. The ooplasm contains numerous lipid inclusions, a syncytium, and secretory cells. From December, stage V oocytes are mainly present, indicating the activity phase of maximum secretion. Yolk platelets accumulate in the oocyte ooplasm, and chorion forms at the zona pellucida. In January, the first smooth eggs are found in some octopuses' ovary, with their proportion increasing steadily. This study aimed to investigate the mitogenic action of gonadotropin and identify the periods of intense cell multiplication during the sexual cycle using cytological methods.