Question

evidence logged: platyhelminthes includes both parasites and free - living forms ✓
outstanding work, detective! youre absolutely correct - flatworms include both parasitic species like tapeworms
and free - living predators like planarians.
clue #6: the microscope station log
you examine the microscope station and find this entry in the logbook:
\today i observed specimens with a complete digestive system - they have both a mouth and an anus! unlike
some other worms, food goes in one end and waste comes out the other. this one - way street makes digestion
much more efficient. i also noticed they have a fluid - filled body cavity, but its not a true one according to my
textbook.\
detective challenge: which phylum has this type of digestive system and body cavity arrangement?
hint: think about which group is round and has that fake body cavity (pseudocoelom) mentioned in an earlier
clue!
whats your answer, detective?

Explanation:

Nematoda (roundworms) have a complete digestive system (mouth and anus) and a pseudocoelom (a fluid - filled body cavity that is not a true coelom). The hint about being "round" also points towards Nematoda.

Answer:

Nematoda