Question

clue #1: the lab assistants note
you enter the crime scene and find a crumpled note on the lab bench. it appears to be from the lab assistant:
\i was organizing the specimens when i noticed something strange. one of the missing containers held creatures that are completely flat - like theyve been run over by a steamroller! these animals have no body cavity and their bodies are shaped like ribbons or leaves. some live freely in water, while others... well, lets just say they prefer to live inside other animals as unwelcome guests.\
detective challenge: what is the name of this phylum?
hint: think about what \flat\ might be called in scientific terms. the name literally means \flatworm\ in greek!
whats your answer, detective?

Explanation:

The description in the note matches the characteristics of flatworms. Flatworms belong to the phylum Platyhelminthes. The hint also indicates that the name means "flatworm" in Greek, which is Platyhelminthes (Platy - flat, helminthes - worm).

Answer:

Platyhelminthes