(Phylum Dicyemida: Dicyemidae) isolated from Korean common octopus in Korea.

Background: Dicyemids are parasites found in the renal sac of cephalopods. The first species of dicyemid was found from kidneys of the Korean common octopus .

Objectives: This study aimed to identify the dicyemid and investigate the effect on renal sac of host.

Methods: In this study, we compared the morphological characteristics of isolate to dicyemids (, , and ) reported from in Japan. We compared the 18S ribosomal RNA (rDNA) and cytochrome c oxidase subunit I (COI) sequences of isolate to the sequences of and . The infected octopuses renal tissues were histologically compared with the tissues of uninfected individuals.

Results: The morphological characteristic of this isolated species corresponds to . The sequences similarities of 18S rDNA and COI gene of isolate are 99.7% and 98.1% with . We observed morphological changes in the epithelia folds of kidney at the dicyemids attached areas.

Conclusions: The present study identified the isolate as and this is the first report of dicyemid species from Republic of Korea. Further studies on the effects of dicyemids on growth and health status of cephalopods will be needed.