Fact 1: Echinoderms lack a centralized nervous system.

Fact 2: Sand dollars and sea biscuits are also echinoderms.

Given the two facts above, answer the question "What lacks a centralized nervous system?" with the following options: 
- Damaged hearing
 - Humans
 - Horses
 - Sand dollars
 - insects
 - Chickens
 - Pesticides
 - barnacles


 

    Sand dollars     