The first record of polystomes (Monogenea: Polystomatidae) from caecilian hosts (Amphibia: Gymnophiona), with the description of a new genus and two new species.

New taxa are proposed for Nanopolystoma lynchi n. g., n. sp. from the urinary bladder and phallodeum of the caecilian Caecilia cf. pachynema and N. brayi. n. sp. from the urinary bladder of C. gracilis, both from South America. These are the first species of polystomatids to be described from caecilian hosts. The parasites are small with a maximum body length of 2 mm. The two gut caeca are not confluent posteriorly and have neither diverticula nor anastomoses. The haptor bears six well-developed suckers and one pair of hamuli. The single follicular testis lies in the mid-body and the ovary is small. Vaginae are present. A single large, operculate egg lies in the short uterus, which leads to an armed genital bulb. Neither the nature of the oncomiracidium nor the phylogenetic position of these worms is known. Nanopolystoma n. g. shares various morphological features with other polystomatid genera; however, the non-confluent gut-caeca lacking diverticula and the presence of skeletal elements in the haptoral suckers place it with the chelonian polystomes of the subfamily Polystomoidinae. These findings suggest that the caecilian host species are probably semi-aquatic. More polystomatid species are expected to be found in association with other species of Caecilia.