1) Agnathan 2) Having a circular mouth 3) Jawless fish 4) Jawless vertebrate 5) Primitive aquatic vertebrate 
Cyclostome is a biological term (from the Greek for `round mouth`) used in a few different senses: ...
• (a.) Alt. of Cyclostomous
any member of the order Cyclostomata (class Agnatha), which contains the lamprey and the hagfish (qq.v.). These fish are characterized by a long ... [14 related articles]
Cy'clo·stome (s?'kl?-st?m), Cy*clos'to*mous (s?-kl?s't?-m?s) , adjective (Zoology) Pertaining to the Cyclostomi. 
[n] - primitive aquatic vertebrate
noun primitive aquatic vertebrate
belonging or pertaining to the Cyclostomata, a subclass of jawless, eellike, marine vertebrates of the class Agnatha, comprising the lampreys and hagfishes. · having a circular mouth.