Answer:
phylum Echinodermata
Sand dollar. Sand dollar, any of the invertebrate marine animals of the order Clypeastroida (class Echinoidea, phylum Echinodermata) that has a flat, disk-shaped body. They are close relatives of sea urchins and heart urchins. The sand dollar is particularly well adapted for burrowing in sandy substrates.
Explanation:
1. The study of all life or living matter.
2. The living organisms of a particular region.
3. The structure, function, and behavior of an organism or type of organism.