PeteAtoms
FormulaRandom
Other than chordates, are there any phyla with species that currently live in the ocean but whose ancestors were terrestrial? I would think there might be some arthropod examples of this, but are there?
EDIT: I should specify "fully aquatic", as in they don't spend any part of their life cycle on land.
Whales? Just throwing that out there, I should've googled "phyla" and "chordates" before I answered though...