Abstract
The isopod Caecognathia robusta (G.O. SARS, 1879) is recorded from the suboscular cavity of the demosponge Geodia mesotriaena (Hentschel, 1929) from the north east Greenland slope. Adult males and females as well as early larval stages were found. The size of G. mesotriaena ranged from 3 to 115 mm diameter, with oscular sizes of < 0.5–11 mm diameter. C. robusta was found in oscules ranging from 1-4 mm diameter, i.e. in G. mesotriaena with a size of 2–92 mm diameter. Neither adult nor larval stages of C. robusta were found in association with other host organisms in our samples.