XENOCOELOMORPHA: a small phylum of bilaterian invertebrates, consisting of Xenoturbellida and Acoelomorpha
ACOELOMORPHA: subphylum of about 350 species of very early bilaterian animals that comprise a sister clade to other bilaterians near the base of Deuterostomia
XENOTURBELLIDA: a subphylum known by only a single genus, Xenoturbella, the first species discovered in the North Sea and described in 1949
the most basic bilaterian animals
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Acoelomorpha
lack a fluid-filled body cavity
worldwide distribution and are found mostly in marine and brackish environments
ANATOMICAL FEATURES:
dorsoventrally flattened
ventral mouth
ciliated
lack CNS
statocysts at anterior end
Roscoff worm/mint sauce worm gets it green colour from intracellular symbiotic algae
forms a triptych
live in colonies
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Xenoturbellida
contains a small number of marine benthic worm-like species
ANATOMICAL FEATURES
dorsoventrally flattened
acoelomate
ventral furrow on each side until stopped by anterior circumferential furrow
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