Which of the following sets of animals belong to same phylum?
A. Swallowtail butterflies, Rat flea, Houseflies - Phylum Arthropoda (jointed appendages)
B. Starfish - Phylum Echinodermata, Catfish - Chordata, Crayfish - Arthropoda
C. Tapeworm - Platyhelminthes (Flatworms), Hookworm - Aschelminthes (Round Worms), Silkworm - Arthropoda.
D. Portuguese man o' war - Cnidaria (Sac-like animals), Razor Clam - Mollusca (Soft-bodied or Shelled Animals), Electric rays - Pisces.
So, the correct answer is option A.