What is the difference between ostia and osculum?

Osculum: A large opening in a sponge through water flows out of the sponge. the sponge may have more than one Osculum.

Ostia: A series of tiny pores all over the body of a sponge that let water into the sponge. One of these is called Ostium. 

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.