Dicyemid mesozoans are endoparasites found in the renal sacs of benthic cephalopods. Adult dicyemids insert the distinct anterior region, termed a “calotte,” into renal tubules of the host. We cloned cDNA encoding chitinase-like protein from the dicyemid Dicyema japonicum (Dicyema-clp1), and also cloned the gene fragment corresponding to the cDNA. Dicyema-clp1 has the hydrophobic amino acid–rich region, but not the chitin-binding domains at the C terminus. Analyses using the SignalP prediction program suggest this hydrophobic amino acid–rich region is the anchor sequence to plasma membranes. The putative catalytic site in glyco18 domain exhibited 1 substitution from aspartic acid to asparagine. The gene fragment had short 9 introns (22–26 bp), and the coding sequence consisted of 10 exons (30–233 bp). Specific and strong expression of Dicyema-clp1 was detected in the calotte of vermiform stages by whole mount in situ hybridization. N-acetyl-d-glucosamine was detected on the outer surface of both peripheral cells of dicyemids and epidermal cells of host renal appendages. Dicyema-clp appears to be associated with N-acetyl-d-glucosamine in the interface between dicyemid peripheral cells and epidermal cells of the host renal appendage, and possibly aids in adhering the calotte to host epidermal cells.