Starfish larvae don't resemble the adult starfish at all. They undergo a fascinating transformation when they live in the plankton.
Echinoderms like star fish and sea-urchins all start their larval development as this Blastula
Bivalve mollusc larvae already resemble the adult form. These will probably become mussels
Trochophore larvae are the larvae of Bristle worms. (Polychaetes) They are very common in the plankton. This 'Mitraria larva' has elongated bristles
Tunicates live part of their lives in the plankton. There are some very interesting aspects about these organisms
A sea urchin larva, accompanied by a small colony of Phaeocystis. Sea urchin larvae develop glass-like structures that support the body
Barnacle larvae undergo several stages. Before they attach to a substrate and start their sessile life they swim in the plankton as this nauplius larva
A gastropod larva, the still transparent shell gives a nice glimpse of the anatomy.
Polychaete larvae are often quite grotesque. This Magelonid larva develops elongated palps.
Ectoprocts are aquatic organisms that used to be called Bryozoa, or Moss animalcules.