A minor phylum of mesozoan worms which are internal parasites of a range of marine invertebrates.‘They are now believed to be made up of two, possibly unrelated, groups: the Dicyemida and Orthonectida.’
- ‘As it turns out, the Orthonectida are almost certainly metazoans, particularly under our stem group definition; but it's anyone's guess whether they, or any other members of the mysterious Mesozoa, are also bilaterians.’
Modern Latin (plural), from Greek orthos ‘straight’ + nektos ‘swimming’ (see nekton).
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