The life cycle of Thelohanellus wuhanensis from Carassius auratus involving an Aurantiactinomyxon-type actinospore

Thelohanellus wuhanensis is an important parasite in crucian carp culture, forming numerous plasmodia on the skin, and causing massive mortality of juvenile fish in soil ponds. During the survey of actinosporeans in oligochaetes of fish pond in Liyang (31°18'N, 119°28'E), an Aurantiactinomyxon-type actinosporean was found from the oligochaete Branchiura sowerbyi. The actinospores are not connected with each other, and possess a style-less spore body with 3 almost equal-sized, elongate caudal processes. In apical view, the spore body is spherical and three polar capsules are positioned on the top of the spore body and close to each other. There is an above 100° angle between each process. Spore body average length (19.8±1.3)μm, width (18.2±1.1)μm polar capsules (4.53±0.4)μm long, (3.4±0.4)μm wide; caudal processes (195.0±15.7)μm long, (11.5±0.8)μm wide. Fresh spores floating in water were collected with 10 μL pipette tip under microscope and stored at -20℃. Genomic DNA was extracted with MagicMag Genomic DNA micro Kit (Sangon Biotech, China) following the instruction. Partial 18S rDNA sequence was amplified with primers MyxospecF and MyxospecR (Fiala 2006). Positive PCR products were sequenced with the primers in Sangon Biotech. Homologous sequences were determined by performing a BLASTN search at NCBI. DNA sequence similarities were calculated using the MEGA 6.0 software package. On the basis of 18S rDNA sequence analysis, the actinosporeans reported here were identified as T. wuhanensis, and showed 99.8%-100% sequence similarity with T. wuhanensis (HQ613410, JQ088179, JQ690370 and JQ968687) available in GenBank. Phylogenetic analysis revealed the actinsporean stages of most taxa in the clade Thelohanellus developed in alternative host Branchiura sowerbyi.