A new deep-sea species of epibenthic acornworm (Hemichordata, Enteropneusta)

摘要

Individuals of an enteropneust, Tergivelum baldwinae n. gen., n. sp. werevideotaped at a depth of about 4 km in the eastern Pacific and collected by aremotely operated vehicle. The living worms range in length from 9 to 28 cmand are dark brown anteriorly and beige posteriorly. The proboscis is shapedlike a shallow dome, indented on either side by a laterodorsal fossa housing aprominent proboscis nerve. The collar comprises a thin transverse crest dorsallyand two laterally projecting lips on either side of the mouth ventrally. Themouth is oriented parallel to the substratum and is flanked by large left andright buccal muscles (contrasting with the rudimentary musculature elsewherein the body). The respiratory pharynx of the trunk extends far anteriorly sothat much of it lies do sal to the mouth opening. The gill bars are not joinedby synapticles. The late rodorsal body wall at the anterior extremity of the trunkextends as two conspicuous flaps (back veils) that run posteriorly as unattachedcoverings over the ante:ior 30-50% of the trunk. On either side of the midline,the body wall of the trunk is extended as a narrow lateroventral fold. Within the trunk runs the intestine, which lacks hepatic sacculations and opens at ananus at the posterior end of the body. Frame analysis of videotapes suggeststhat the worm can secrete a mass of mucus around the body to facilitatedemersal drifting from one epibenthic foraging site to the next. We include apreliminary phylogenetic analysis based on rDNA sequences from T baldwinaen. gen., n. sp. and additional deep-sea enteropneusts not yet formally describedtaxonomically (sequence data place them unexpectedly close to ptychoderids).Until more is known about the group as a whole, it is prudent to leave familylevel classification of T baldwinae n. gen., n. sp. as incertae sedis.