Homalopoma subobsoletum is a species of small sea snail with calcareous opercula , a marine gastropod mollusk in the Colloniidae family . Homalopoma subobsoletum is a species of small sea snail with calcareous opercula , a marine gastropod mollusk in the family Colloniidae . Homalopoma subobsoletum is a species of calcareous sea snail with small opercula , a marine gastropod mollusk in the family Colloniidae .