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An excavating sponge, which covers extensive areas of limestone rock, has been found at several locations of the Eastern Mediterranean Sea. This zooxanthellate clionaid, brown with yellow oscula, may have an extension of several square meters under the β-form, similar to what has been described in coral reef areas. It has been observed at 3–30 m depth, generally in clear water in the Ionian Sea, Crete, Cyprus and Lebanon. The gross morphology and the spicule characters are described from all the collected specimens. The spicule complement, with variable tylostyles and rare, sometimes absent, thin spirasters, is compared with that of Cliona parenzani Corriero & Scalera-Liaci 1997 from the Apulian coast (Ionian Sea, Mediterranean Sea), and of several Caribbean and Indo-Pacific clionaid species, which display the same morphology and rather similar spicule characters. The sponge is tentatively identified as C. parenzani, although there are some differences with the type specimens in the highly variable spiculation, suggesting that it may represent a species complex similar to what is known for other species in the Caribbean and Indo-Pacific areas. Although the sponge appears to be closely related to large brown spreading clionaids from tropical areas and was previously practically overlooked in the Eastern Mediterranean, it does not appear to be a recent introduction. It is suggested that it could be a survivor in the warmer area of the Mediterranean of an ancient thermophilous fauna, which did not survive in the colder Western Basin during glacial episodes of the Pleistocene. [ABSTRACT FROM AUTHOR]