You have probably heard of crustaceans, mollusks and anemones before...
Banded clinging crab
Flamingo tongue
Closed giant anemone
... but would you recognize hydroids, crinoids and zoanthids?
Christmas tree hydroids
Golden crinoid
What about corallimorphs or sea slugs?
Corallimorphs
Warty corallimorphs
Once you tune into these unique creatures they start to pop-out at you along the reefs. With time, one gets much better at recognizing these interesting shapes and/or colors. Though I must admit it's still quite a learning curve to comprehend just what kind of animal they actually are, even with the reference books.
Tunicates are a recent discovery. The shapes and colors drew me in (not easy to miss the strawberry tunicates) and the incurrent & excurrent siphons confirmed their identity.
Green tube tunicate (next to a sea pearl)
Reef tunicate