Thelohanellus testudineus n. sp. (Myxosporea: Bivalvulida) infecting the skin of allogynogenetic gibel carp Carassius auratus gibelio (Bloch) in China.

A Thelohanellus species was encountered during a survey on Thelohanellus diversity of Carassius auratus gibelio (Bloch) in China. The infection is characterized by the presence of large cysts of 1.4-3.2 cm in diameter in the skin of host. Mature spores were ampullaceous in frontal view and testudinate in lateral view, measuring 19.7 ± 0.7 (18.6-20.8) μm long, 7.6 ± 0.4 (6.6-8.4) μm wide and 7.3 ± 0.5 (6.6-8.8) μm thick. The single polar capsule was elongated pyriform, with 11.1 ± 0.5 (10.0-11.9) μm long and 5.3 ± 0.3 (4.3-5.8) μm wide. Polar filaments coiled with 7-8 turns. Scanning electron microscopy revealed a smooth spore surface with flat side and convex side. The sutural line was straight or 'S' like, running near the middle of the valves. Histologically, the large cysts consisting of numerous small plasmodia developed in the dermis of the skin. The BLAST search indicated that the newly obtained ssrRNA gene sequences did not match any available sequences in GenBank and phylogenetic analysis placed it in the Thelohanellus clade. Based on morphology and molecular differences with reported Thelohanellus spp., this parasite was described as a new species of genus Thelohanellus.