ventral, solid hollow and single. and double. . Pharynx perforated by gill slits.
Gill slits are absent. . Heart is ventral. Heart is dorsal (if present).
. A post-anal part (tail) is present. Post-anal tail is absent. .
. . Class – Cyclostomata Class – Cyclostomata Class – Cyclostomata Class – Cyclostomata Class – Cyclostomata All living members of the class Cyclostomata are ectoparasites on some fishes. They have an elongated body bearing - pairs of gill slits for respiration.
Cyclostomes have a sucking and circular mouth without jaws (Fig. . ). 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). . .
. Class – Chondrichthyes Class – Chondrichthyes Class – Chondrichthyes Class – Chondrichthyes Class – Chondrichthyes They are marine animals with streamlined body and have cartilaginous endoskeleton (Figure . ). Mouth is located ventrally.
Notochord is persistent throughout life. Gill slits are separate and without operculum (gill cover). The skin is tough, containing minute placoid scales . Teeth are modified placoid scales which are backwardly directed.
Their jaws are very powerful. These animals are predaceous. Due to the absence of air bladder, they have to swim constantly to avoid sinking. Vertebrata Division Agnatha (lacks jaw) Class .
Cyclostomata Gnathostomata (bears jaw) Super Class Pisces (bear fins) Tetrapoda (bear limbs) Class . Amphibia . Reptilia . Aves .
Mammals Class . Chondrichthyes . Osteichthyes The subphylum Vertebrata is further divided as follows: Figure . A jawless vertebrate - Petromyzon Figure .
Example of Cartilaginous fishes : (a) Scoliodon (b) Pristis Heart is two-chambered (one auricle and one ventricle). Some of them have electric organs (e.g., Torpedo ) and some possess poison sting (e.g., Trygon ). They are cold-blooded ( poikilothermous ) animals, i.e., they lack the capacity to regulate their body temperature. Sexes are separate.
In males pelvic fins bear