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Planaxis sulcatus is a Gonochoristic species (i.e. Individuals with distinct and separate sex) despite suggestions of them undergoing parthenogenetic development in the Indian Ocean cryptic species as no males were observed there (Houbrick 1987; Ohgaki 1997). However, it was thought that the previous authors who made the suggestion that P. sulcatus might be parthenogenetic have overlooked copulation behavior and the existence of males due to biasness in sampling techniques (Houbrick 1987; Ohgaki 1997).
In early spring, individuals of P. sulcatus will migrate down shore and stay at the lower levels during spring and early summer to prepare for mating (Ohgaki 1997). P. sulcatus were observed to breed in the summer months where pairing behavior (i.e. copulation) between male and female individuals was frequently observed (Ohgaki 1997). Female individuals of P. sulcatus are generally larger than males (Ohgaki 1997). New recruits of P. sulcatus settlers appeared in autumn where it continues to grow and develop till maturity (Ohgaki 1997). P. sulcatus were observed to reach sexual maturity within the first year of settlement (Ohgaki 1997). First year recruits will merge into the population of older-year the following autumn after they settle (Ohgaki 1997).
The proportions of females to males were observed to increases as size increases in each population of P. sulcatus (Ohgaki 1997). This observation could be attributed to either sex reversal from male to females as the snails grow or due the faster growth of females than of males (Ohgaki 1997). The latter might be a more probably explanation to this observation since no gonads in a transition stage from testis to ovary were observed (Ohgaki 1997).
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