Most arthropods and some mollusks and tunicates have circulatory systems, which means fluid transporting nutrients and oxygen flow directly into internal organs.

a. closed
b. nonexistent
c. open

Match the following terms and definitions. 1. species that are adapted to live in equilibrium at carrying capacity population density 2. population growth that reaches equilibrium and carrying capacity population 3. death rate mortality 4. birth rate k-selected 5. a group of interacting individuals of the same species within the same geographic area natality 6. the number of organisms living in a particular area logistic growth