Phylum Annelida
Step-by-step explanation:
The given animal must be an Annelid.
Annelids are commonly called segmented worms. The characteristics features of annelid are:
- Segmented bodies , each segment is called annuli.
- Closed circulatory system.
- Stiff appendages and flexible skin.
- Eucoelomate i.e the presence of true coelom.
- Nephridia as excretory organs.
Since the animal discovered by the marine biologist has a segmented body and true coelom, it is obviously categorized in Phylum Annelida.