A new host for Hematodinium infection among lithodid crabs from the Sea of Okhotsk

[Display omitted] •A disease caused by Hematodinium was founded in Hapalogaster grebnitzkii.•It was a new host for this agent among lithodid crabs from the Sea of Okhotsk.•We conducted a study of macro- and micromorphological signs of the disease.•We identified of Hematodinium sp. from soft crabs based on 18S RNA sequence data. A disease caused by parasitic dinoflagellates of the genus Hematodinium has been found in the soft crab Hapalogaster grebnitzkii from the Sea of Okhotsk, which is considered a new host for this agent among lithodid crabs. This report provides macro- and micromorphological descriptions (using light and transmission electron microscopy) of the disease, as well as molecular identification of Hematodinium sp. from soft crabs, based on 18S RNA sequence data.