All living members of the class Cyclostomata are: 

The correct answer is Ectoparasite 

Explanation:

Cyclostomata is a class under the phylum Chordata which being the highest phylum has bilateral symmetry.This group includes jawless fish like hagfish and lampreys. They exhibit bilateral symmetry, not radial symmetry.

Characteristics of Cyclostomata:

• All living members of the class Cyclostomata are ectoparasites on some fishes.
• They have an elongated body bearing 6-15 pairs of gill slits for respiration.
• Cyclostomes have a sucking and circular mouth without jaws
• Their body is devoid of scales and paired fins.
• Cranium and vertebral column are cartilaginous.
• Circulation is of closed type.
• Cyclostomes are marine but migrate for spawning to fresh water.
• After spawning, within a few days, they die. Their larvae, after metamorphosis, return to the ocean.
• Examples: Petromyzon (Lamprey) and Myxine (Hagfish).