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Balanoglossus : ウィキペディア英語版 | Balanoglossus
''Balanoglossus'' is an ocean-dwelling acorn worm (Enteropneusta) genus of great zoological interest because, being a Hemichordate, it is an "evolutionary link" between invertebrates and vertebrates. ''Balanoglossus'' is a deuterostome, and resembles the Ascidians or sea squirts, in that it possesses branchial openings, or "gill slits".It has notochord in the upper part of the body and has no nerve chord. It does have a stomochord, however, which is gut chord within the collar. Their heads may be as small as 2.5 mm (1/10 in) or as large as 5 mm (1/5 in). ==Discovery== J.F. Eschscholtz who discovered Balanoglossus in 1825 in Mashail Island described it as a worm-like holothurian. The discovery of gill-slits in this animal by Kowalewsky (1865) led to creation of a special class Enteropneusta by Gegenbaur (1870). Bateson (1885) included them in Phylum Chordata. Hyman (1959), however, placed them near Echinodermata and gave Hemichordata a status of an independent phylum.
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