Question

A marine biologist dredges up a small animal from the bottom of the ocean. it is uniformly segmented, with short, stiff appendages and soft, flexible skin. it has a complete digestive system and a closed circulatory system, plus multiple true coeloms. based on this, you determine that the animal must be a(n) _____.

Answer 1

First, a complete digestive system means that the digestive tract has a beginning or the oral end and the opposite end or the aboral end. This is found in more complex animals starting from roundworms (flatworms have an incomplete digestive tract). A closed circulatory system is found in animals more recent than mollusks. The presence of the coelom makes it more evolved than the flatworms. 

Specifically, a small animal with a segmented body, short stiff appendages, and soft skin with the above characteristics point out to the phylum Annelida or annelids.