Answer:
they have certain functions and or adaptations that allow them to move without spines
Explanation:
internal-organ function, breathing, digestion, and heartbeat. This system consists of two complementary parts: the sympathetic and parasympathetic systems.
If you look at the taxonomic classification there are 7 levels and they are 1. Kingdom; 2. Phylum; 3. Class; 4. Order; 5. Family; 6. Genus and 7. Species.
The taxonomic level phylum includes greatest number of species for a given genus.