xaiTrl, hair, g obs, foot), a zoological class, including the majority of the Annelida, and indeed, save for the Echiuroidea, co-extensive with that group as usually accepted.
This form of nephridia leads to the shorter but essentially similar organs in the Polychaete Sternaspis, and to those of the Echiuroidea (q.v.) and of the Gephyrea.
There appears to be little either in the development or in the structure of the Haplodrili to warrant the view held by Hatschek and Fraipont that Polygordius and Protodrilus are exceedingly primitive forms, ancestral to the whole group of seta-bearing Annelids (Oligochaeta, Polychaeta, Hirudinea and Echiuroidea).
SIPUNCULOIDEA, marine animals of uncertain affinities, formerly associated with the Echiuroidea in the group Gephyrea.
They are divided as follows: (i) Haplodrili or Archiannelida; (2) Chaetopoda; (3) Myzostomida, probably degenerate Polychaeta; (4) Hirudinea (see CHAETOPODA and LEECH); (5) Echiuroidea.
There is a definite Annelid group (see Annelida), including the Archiannelida, the bristleworms (see Chaetopoda), of which the earthworm (q.v.) is the most familiar type, the Myzostomida, Hirudinea (see Leech) and the armed Gephyreans (see Echiuroidea).
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