AP BIOLOGY

Detailed explanation-1: -Annelids have a coelom, closed circulatory system, excretory system, and complete digestive system. They also have a brain.

Detailed explanation-2: -The internal organs of annelids are well developed. They include a closed, segmentally-arranged circulatory system. The digestive system is a complete tube with mouth and anus. Gases are exchanged through the skin, or sometimes through specialized gills or modified parapodia.

Detailed explanation-3: -The polychaete digestive system is generally a straight tube; a mouth leads into an esophagus, which is followed by the intestine and the anus. Some free-moving forms have a proboscis that can be thrust forward by being turned inside out-that is, the proboscis is eversible.

Detailed explanation-4: -Like mollusks, annelids exhibit protostomic development. Annelids are bilaterally symmetrical and have a worm-like appearance. Their particular segmented body plan results in repetition of internal and external features in each body segment. This type of body plan is called metamerism.