Biology · Animal Kingdom · NEET
They are ECTOPARASITES (ecto = outside). All living members of Cyclostomata attach to the OUTSIDE of a host fish using their circular sucking mouth and feed on its blood and body fluids. An endoparasite would live INSIDE the host (like a tapeworm), which is wrong here. NEET 2025 asked exactly this and the answer was 'Ectoparasite'. Never pick 'endoparasite', 'symbiotic' or 'free-living' for Cyclostomata.
No. This is their single most important feature. Cyclostomes belong to the division Agnatha, which means 'without jaws'. Instead of jaws they have a round, sucking mouth. Because they lack jaws they cannot bite; they rasp and suck. Any statement that pairs 'jaws' or 'upper and lower jaw' with Cyclostomata is a trap.
They are the oldest and simplest group of living vertebrates. NCERT calls them 'the most primitive chordates'. They lack jaws (a later evolution), lack paired fins, lack scales, and their skeleton is still cartilage instead of bone. All these 'missing' advanced features make them primitive. They sit at the base of vertebrate evolution, just above the jawless line Agnatha.
CARTILAGINOUS. Their cranium (skull) and vertebral column are made of cartilage, not bone. Students confuse this with Chondrichthyes, which are ALSO cartilaginous. Both are cartilaginous, but Chondrichthyes have JAWS, scales and paired fins, while Cyclostomata have NONE of these. So 'cartilaginous' alone cannot separate them - use the jaw.
Both have a cartilage skeleton, but that is where the similarity ends. Cyclostomata: jawless, circular sucking mouth, NO paired fins, NO scales, ectoparasite, most primitive (e.g. Petromyzon, Myxine). Chondrichthyes: have jaws, paired fins, placoid scales, are predators/free-living (e.g. Scoliodon, Pristis). The jaw is the fastest way to tell them apart in an exam.
The two NCERT examples are Petromyzon (Lamprey) and Myxine (Hagfish). NEET loves to test these scientific-to-common name pairs. Remember: Petromyzon = Lamprey, Myxine = Hagfish. In NEET 2024 'Myxine - Hag fish' was the correct match.
No, they have NEITHER. NCERT says their body is 'devoid of scales and paired fins'. This is why NEET 2016 statement 'All cyclostomes do not possess jaws and paired fins' was correct. If a question says cyclostomes have fins or scales, it is false.
They have 6 to 15 pairs of gill slits, used for respiration. A NEET match-column question paired '6-15 pairs of gill slits' with Cyclostomes. Note Petromyzon has 7 pairs in one 2026 question - that still falls inside the 6-15 range.
All living members of the class Cyclostomata are:
Choose the correct statement.
A group of researchers found fish-like animals with: (A) cartilage endoskeleton, (B) ectoparasitic, attached to fish skin by a circular sucking mouth, (C) no paired fins or scales but 7 pairs of gill slits. Which species fits best?
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Lamprey is Petromyzon and Hagfish is Myxine. Both are NCERT examples of class Cyclostomata and are frequently tested in NEET name-matching questions.
They are mainly marine (live in the sea) but migrate to fresh water for spawning. After spawning they die within a few days, and their larvae, after metamorphosis, return to the ocean.
They have a closed type of circulation, meaning blood always flows inside vessels and never freely bathes the organs.
It is a vertebrate. Cyclostomes have a cartilaginous cranium and vertebral column, so they are true vertebrates - in fact the most primitive living vertebrates.
Agnatha means 'no jaws'. Cyclostomes have no jaws, only a round sucking mouth, so they are the only living class placed under the division Agnatha. Jawed vertebrates go under Gnathostomata.
