Class Cyclostoma

• Cyclostomes are endoparasites on some fishes.
• Cyclostomes have an elongated body, without scales and paired fins.
• Cyclostomes have 6-15 pairs of gill slits for respiration.
• Cyclostomes have sucking and circular mouth without jaws.
• Cyclostomes have cartilaginous cranium and vertical column.
• Cyclostomes have closed type circulation.
• Cyclostomes are marine, but they migrate for spawning to fresh water, after spawning they die. Their larvae after metamorphism will return to the ocean.
• Examples of Cyclostomes


  Myxine [Hagfish]

  Petromyzon [Lamprey]
• Class Chondrocytes

  • They have marine have streamlined body.
  • They are predators.
  • They have cartilaginous exoskeleton. Notochord is present throughout life.
  • They have ventral mouth with powerful jaws
  • They have gill slits without operculum [gill covering]
  • They have skin with Placiod scales. these are modified placoid scales which are backwardly directed
  • They have no air bladder they swim constantly to avoid sinking
  • They have separate sexes
  • In males pelvic fins wear claspers
  • They have internal fertilization, many are Viviparous
  • Their development is direct.
• Class Osteichthyes

  • They are marine and freshwater fishes. They have streamlined body.
  • They have a bony endoskeleton.
  • They have terminal mouth.
  • There are four pairs of gills with operculum on each side
  • Scales are sight cycloid, ctenoid, etc.
  • They have airplanes for buoyancy.
  • They also have separate sexes
  • They have external fertilization mostly oviparous.
  • Their development is direct.