Q.Mention the features of cyclostomes.
[!ANSWER] Cyclostomes are the jawless vertebrates, representing the most primitive living vertebrate lineage.
Unlike true fishes (Pisces), cyclostomes such as lampreys and hagfish lack jaws altogether, feeding instead through a circular, sucking or rasping mouth, often used to attach to and feed parasitically on other fish (as in lampreys) or to scavenge on dead/dying animals (as in hagfish). Cyclostomes also lack paired fins (no pectoral or pelvic fins), unlike jawed fishes. Internally, the notochord persists throughout life without being replaced by a series of bony or cartilaginous vertebral centra, and respiration occurs through a series of gill pouches rather than the open gill slits of jawed fishes. Cyclostomes are considered the most primitive living vertebrate group, retaining a body plan closer to the earliest vertebrates than any jawed fish.
[!ANSWER] Cyclostomes (lampreys, hagfish): jawless, finless (no paired fins), a persistent notochord (no vertebral centra), gill pouches, and a sucking/rasping circular mouth — the most primitive living vertebrates.
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