What is the role neurohormones in annelied?

The brain of most annelids (phylum Annelida; segmented worms, including the leeches and terrestrial earthworms) is relatively simple in structure. The earthworm brain is a bilobed mass lying above the pharynx in the third body segment. Sensory nerves leave the brain and run forward into the prostomium (extreme anterior end) and first segment. The brain of the active, predatory polychaetes (a class of marine worms) is more complicated. In some the brain can be divided into a forebrain, a midbrain, and a hindbrain; a single pair of circumesophageal or circumpharyngeal connectives leave the brain, surround the anterior gut, and connect with the ventral nerve cord.

clumped distribution, because you'de have all of the population gathered in a relatively small are.

it's the most common because it provides protection and a mate for reproduction

example: humans, seeweed, cattles, etc.