The histology of the ovotestis and the reproductive cycle of Pythia plicata a salt marsh snail inhabiting the Pitchavaram mangroves was studied.  This snail exhibits a protandrous sexual cycle. First sexual maturity is attained at a shell length of 10.0mm. The male phase starts in November (a NE monsoon month) when the male reproductive organs are well developed. The female genital ducts start developing in January (a NE postmonsoon month). Up to the end of March (end of postmonsoon season) the bursa copulatrix is filled with mucus without any foreign sperms. The penis and the anterior part of vasdeferens are present throughout the year. Copulation take place from April (early summer) onwards, mostly during the night. Egg laying starts from the end of June and extends upto the end of July (Postsummer season to early NE premonsoon). During August and September (NE premonsoon months) the ovotestis is completely empty and devoid of the sex cells. Then this cycle is repeated during the next year.