Explanation
This is an acronym to help you remember that, other than tetra radial symmetry, the calcareous ossicle endoskeleton is the only characteristic shared by all 5 classes of this Phylum. The first letter of each word gives you the first letter of what it stands for.
- Asteroidea (All)
- Holothuroidea (Have)
- Crinoidea (Calcareous)
- Ophiuroidea (Ossicle)
- Echinoidea (Endoskeleton)