In which one of the following options, a category of animals is correctly described with no single exception in it?
All echinoderms are marine, with a water vascular system which helps in locomotion, food capture and respiration.
Parapodia are present only in polychaetes (e.g. Nereis); not in all annelids.
Presence of three pairs of legs is a characteristic feature of insects (not all arthropods).
Among molluscs, cephalopods have a closed blood vascular system.