Category: Transparent or Jelly-Like

Cladocerans

Commonly called "water fleas."  Bear a large, anterior compound eye, and carapace covering most of the body.

Ctenophores

Transparent marine animals with eight rows of cilia.  Body is ~97% water, size from a few mm to several cm.

Jellyfish

Often transparent, bell-shaped marine animals with hanging tentacles; body more than 95% water; size varies.

Pelagic Tunicates

Nearly transparent marine animals, body mostly water.  Four pelagic groups: salps, doliolids, appendicularians, and pyrosomes; each is covered by a thin or thick tunic.  

Siphonophores

These are colonial animals, mostly transparent, with many specialized parts; relatives of jellyfish. A pneumatophore is a gas-filled float positioned at the top of the colony in some siphonophores.