Kerang Totok (Polymesoda erosa) merupakan jenis bivalvia yang banyak ditemukan di kawasan hutan mangrove di Segara Anakan, Cilacap. Tujuan penelitian ini adalah untuk mengetahui struktur gonad kerang totok pada beberapa tingkat kematangan gonad melalui studi histologis. Enampuluh sampel kerang totok diambil dari Pulau Gombol, Laguna Segara Anakan, Cilacap, selama bulan Mei sampai Agustus 2002 untuk diamati gonadnya secara makroskopis dan histologis. Hasil penelitian menunjukkan bahwa pada sampel kerang jantan dan betina ditemukan tiga tingkat kematangan gonad dan stadia gonad yang Belum dapat diidentifikasi jenis kelaminnya. Diameter oosit meningkat sejalan dengan tingkat kematangan gonadnya dengan kisaran 38 – 100 μm. Diameteroosit rata-rata pada tigkat kematangan gonad I, II dan III berturut-turut adalah 58,8 μm; 66,4 μm and 77,2 μm.Kata kunci : Histologi, gonad, tingkat kematangan gonad, Polymesoda erosaMangrove clam, Polymesoda erosa is an economically valuable bivalvia species which is commonly consumed and has a potential to be cultured in Indonesia. The aim of this research was to understand gonad structure ofthe clams at different gonad maturity stages by histologycal study. The samples were taken monthly on May to August 2002 at Gombol iskand of Laguna Segara Anakan, Cilacap. Sixty samples were used examinevisually for gonad maturity and then were studied histologically. The results of present works revealed that there were 3 gonad maturity stage of the samples both at female and male samples as well as unidentifiedsex samples. Diameter of oocytes increased following the maturity of the gonad. The rage of diameter oocytes wer 38 – 100 μm. Average diameter of oocyte during gonad maturity stage 1, 2 and 3 were 58,8 μm; 66,4 μm and 77,2 μm respectively.Key words : Histology, gonad, maturity stage, Polymesoda erosa