1 0 0 0 0 2 1 0 3 0 Glottidia spp.
, Mollusca, Cephalochordata, and Vertebrata.
Affinities between the Echinodermata, Enteropneusta
, and Chordonia.
Graptolithina with Sections on Enteropneusta
Graptolithina: with sections on Enteropneusta
At present, 135 hemichordate species are described: 121 are solitary Enteropneusta
, or acorn worms; and 24 are colonial, tube-dwelling Ptero-branchia (Appeltans et al.
The phylum Hemichordata is divided into two classes: Pterobranchia and Enteropneusta
The later stages in the development of Balanoglossus kowalevskki, with a suggestion as to the affinities of the enteropneusta
The deuterostome phylum Hemichordata is composed of three extant classes: the Enteropneusta
are solitary worms, the Pterobranchia are colonial tube-dwelling suspension feeders, and the Planktosphaeroidea are known only from their larvae.