All of the following are benthic organisms except
a.) sea star
b.) hermit crab
c.) mussels
d.) tuna

Benthic organisms are those that dwell on the bottom of the sea or on the ocean floor. These include sponges, lobsters, crabs, clams, worms, etc. From the given choices, only the tuna will not qualify being benthic. Thus, the answer is letter D. 

Neurotransmitters are messengers responsible for communication between neurons. they are released from synaptic vesicles and are received by receptors.  the communication is referred to as neurotransmission. the following statement is true about neurotransmitters: a. they're stored in synaptic vesicles in the axon.