Portraits of Galeommatoidea

ABSTRACT Galeommatoidea are bivalves with small (usually 1–15 mm), fragile, sometimes vestigial, shells, occurring free-living or in association with other benthic invertebrates from the intertidal to depths in excess of 7,000 m. They are the most diverse but least studied and most underrepresented group of bivalves in biodiversity surveys and museum collections. The majority of commensal species of Galeommatoidea have dull, frequently uncoloured, unsculptured shells, but free-living species have papillate, sometimes coloured, mantles; they can be gregarious, and superficially resemble crawling gastropods. Many species of Galeommatoidea remain to be discovered, and we argue that future descriptions of free-living new species should ideally include photos of living animals, while many of the historically known species described based on their shells will probably be best treated as nomina dubia.