On the one hand the Turbellaria are considered to be an offshoot of the early Coelomate stock, on the other they are held to be descendants of a simpler two-layered stock.
The conception of the Dipleurula derives its chief weight from the fact that it is comparable to the early larval forms of other primitive coelomate animals, such as Balanoglossus, Phoronis, Chaetognatha, Brachiopoda and Bryozoa.
PRIAPULOIDEA, a small group of vermiform marine creatures; they have been usually placed in the neighbourhood of the Gephyrea, but their position is uncertain and it is doubtful if they are to be regarded as coelomate animals.
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