Histomorphological studies of the testis and male genital ducts of Supachai's caecilian, Ichthyophis supachaii Taylor, 1960 (Amphibia: Gymnophiona)

We investigated the structure of the male reproductive system in Ichthyophis supachaii . The testis comprises a series of mulberry‐like lobes, each of which contains testis lobules occupied by germ cysts. A single cyst consists of synchronously developing germ cells. Six spermatogenic cell types, viz. primary spermatogonia, secondary spermatogonia, primary spermatocytes, secondary spermatocytes, spermatids and spermatozoa, have been identified and described. Notably, the testis of I. supachaii encompasses specific organization patterns of spermatids and spermatozoa during spermiogenesis. Spermiating cysts rupture and release spermatozoa to the collecting ducts, which are subsequently transported to the sperm duct, Wolffian duct and cloaca. We report for the first time ciliated cells in the epithelium of the caecilian Wolffian duct. The cloaca is divided into the urodeum and phallodeum. The urodeum has ciliated and glandular epithelia at its dorsolateral and ventral regions, respectively, as the lining of its internal surface. The muscular phallodeum is lined by ciliated epithelium. Paired Mullerian ducts lie parallel to the intestine and join the cloaca. The posterior portion of the duct is modified as the Mullerian gland. The most posterior region is non‐glandular and lined by ciliated epithelium. Our findings contribute further to information on the reproductive biology of caecilians in Thailand.