Abstrait

A NEW TORQUAQRATORID ACORN WORM (HEMICHORDATA, ENTEROPNEUSTA) AND ITS ACOELOMORPH ASSOCIATE FROM THE ABYSSAL GULF OF CALIFORNIA, MEXICO

Nicholas D. Holland*

During the last fifteen years, the known diversity of acorn worms (enteropneust hemichordates) increased conspicuously with the recognition of a fourth family, the Torquaratoridae. Representatives of the new family typically crawl on the surface of the deep-sea floor in contrast to other acorn worms, most of which inhabit burrows in relatively shallow water. Because the deep ocean is so vast and difficult to sample, torquaratorid diversity will only become evident by exploring previously unsampled regions-one of these is the abyssal Gulf of California (Mexico). The present study describes the most abundant torquaratorid species found living on the deep-sea floor in the southern Gulf of California. By means of a remote operating vehicle, worms were video-recorded alive at depth and then collected by suction sampler and brought to the surface. On the basis of both morphological and molecular data, the new acorn worm species belongs to the previously described genus Yoda (the only acorn worm genus known to be hermaphroditic) and has been named Yoda osborni n. sp. An unexpected additional discovery was that the new acorn worm species is associated with acoelomorph worms (likely commensals) living in the pharyngeal lumen. These acoelomorphs are described here as Thalassoanaperus abyssalis n. sp.; they are noteworthy because almost all of their relatives in the clade Convolutidae are free-living and inhabit shallow depths.