Balanoglossus

Balanoglossus, a genus of marine worms to which considerable attention has of late years been directed as the possible ancestor of the Vertebrates. The body is composed of three regions: (1) a long worm-like trunk, distinctly ringed at the hinder end, and with a series of pairs of respiratory pores at the anterior end; (2) a collar round the latter portion of the trunk; (3) a contractile proboscis. There is a horizontal bar (described as the "notochord," (q.v.) beneath the alimentary canal which is compared with the vertebral column of the Chordata (q.v.); the canal in this bar is often said to be homologous with the neural canal of the vertebrates, though it occurs in other worms and Gephyreans (q.v.). Balanoglossus certainly has resemblances to Amphioxus, but according to the most recent views the structure of the nervous system (a ring round the mouth from which two cords run back along the body) and the fact that the supposed "notochord" is below the main blood-vessel prove that it is a true worm.

Balanoglossus lives in mud in warm and temperate seas, as the Mediterranean, round the Channel Isles, and off the coast of Florida. The embryo is known as Tornaria and most resembles the Bipinnaria (q.v.) stage of Starfish.