Crayfish, jellyfish, and shellfish are true fishes.

a. True

b. False

False.

Explanation:

Fishes or Pisces are the true vertebrates that contain two chambered hearts. They use gills or lungs for the respiration and are endothermic in nature. They have well developed advance characters than invertebrates.

Jelly fish is included in the phylum cnidaria. Cray fish belongs to the phylum arthropoda and shell fish, all are included in the phylum invertebrates. They are not true fishes.

Thus, the correct answer is option (b).