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Abstract The reproductive cycle and sexuality studies of the mussel Brachidontes pharaonis were carried out during the period from March 2016 to February 2017 along Alexandria Coast, Egypt. The gametogenic development of the gonads and the spawning duration under natural conditions were also studied. Histological preparations of a total of 307 individuals were examined monthly and the results showed that 44% were males, 51.8% females, 3.9% were sexually undifferentiated individuals and only one individual was hermaphrodite presenting 0.33% of the examined population, which indicates that B. pharaonis is gonochoristic. Histological studies showed that the gametogenic cycle could be divided into five stages of maturation. Also, an extended period of spawning starting from April to October was detected. Spawning activity of the studied species was in May to July and October. Gonad index reached its maximum in May, August and October when most of the individuals were in ripe and spawning activity. Sexes were distinct all over the studied size classes except those individuals in resting condition (stage 0). The smallest ripe gonads of both sexes were observed at 8.0–12.0 mm shell lengths. Photomicrographs of gametogenic cycles of both male and female mussels are included. [ABSTRACT FROM AUTHOR]

Brachidontes pharaonis (Fischer, 1876) was widely reported to cover completely hard substrates especially rocky shores with higher density in mid-littoral zones forming mytilid beds along Alexandria Coast, Egypt. During our study on the reproductive cycle of this species, one case out of 307 examined specimens was found to be hermaphrodite representing only 0.33% of the total sample. It had a shell length 28.25 mm and was collected during January 2017. The sex ratio of this population is different from 1:1, although this deference was not significant (X 2  = 11.118, df = 11, P > 0.05). In this contribution, this case of hermaphroditism in B. pharaonis is described . The histological study showed the presence of male and female gametes in the same follicle and this was the most common situation in both lobes of the mantle. The male zone was showing different stages of spermatogenesis together with the female zones showed different stages of oogenesis with occurrence of young oocytes attached to the follicle wall. [ABSTRACT FROM AUTHOR]