A minute tube-dwelling colonial acorn worm found chiefly in deep water.
- ‘There are two classes of hemichordate, the pterobranchs and the enteropneusts, which differ greatly in appearance and lifestyle.’
- ‘The SSU data supported enteropneust paraphyly by placing acorn worms of the family Ptychoderidae as the sister to a group consisting of pterobranchs + acorn worms of the family Harrimaniidae.’
- ‘The ciliary bands on the phoronid and brachiopod tentacles are upstream-collecting bands with separate cilia on monociliate cells just like those of larvae or adults of pterobranchs, echinoderms and enteropneusts.’
- ‘Previously, hemichordates were thought to be paraphyletic, with enteropneusts (acorn worms) more closely related to chordates and pterobranchs closer to echinoderms.’
- ‘Ax favors the Pharyngotremata hypothesis, but compiles evidence that not only the hemichordates but also the pterobranchs are paraphyletic grades.’