Complex sentence: The second pair of antennae is located behind the mouth; in all other crustaceans the antennae are in front of the mouth at the adult stage, and only their larvae have antennae that have the same location as adult cephalocaridans.
Split into simpler sentences: The second pair of antennae is located behind the mouth. In all other crustaceans the antennae are in front of the mouth at the adult stage, and only their larvae have antennae that have the same location as adult cephalocaridans.