Which of the following pairs of animal phyla are the most closely related?

a. echinoderms and arthropods
b. annelids and flatworms
c. cnidarians and echinoderms
d. sponges and mollusks

C. Cnidarians and echinoderms is the answer.

There are 3 phyla that sorts worms platyhelminthes (flatworms), nematodes (round worms) and annelids (segmented worms). The closest one is C.

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only about ten percent of the energy at one trophic level is passed on to organisms at the next trophic level. the remainder of the energy is used in life processes or lost as heat.