Information authenticated by Dr Keith Hiscock of the Marine Biological Association of the UK:
http://www.mba.ac.uk/
Larvae: Stage in an animal's lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.
Polyp: Typically sedentary soft-bodied component of cnidaria (corals, sea pens etc), which comprise of a trunk that is fixed at the base; the mouth is placed at the opposite end of the trunk, and is surrounded by tentacles.