PHYLUM HEMICHORDATA :
- Have small worm-like marine animals.
- Was earlier placed as sub-phylum of Phylum Chordata.
- Bilaterally symmetrical, triploblastic and coelomate.
- Body cylindrical, has proboscis, collar and trunk.
- Circulation is open type.
- Respiration by gills
- Excretion by proboscis gland.
- Sexes separate, external fertilization, indirect development.
e.g., Balanoglossus
PHYLUM CHORDATA :
- Presence of Notochord (between gut and nerve cord)
- Have dorsal hollow nerve chord.
- Have paired pharyngeal gill slits.
- Heart is ventral.
- Post anal tail present.
- Bilaterally symmetrical, triploblastic, and coelomate with organ system level of organization.
- Circulation is closed type.
SUB-PHYLA UROCHORDATA :
- Notochord present only in tail of larval stage. e.g., Ascidia, Salpa, Doliolium.
SUB-PHYLA CEPHALOCHORDATA :
- Notochord extends from head to tail. e.g., Amphioxus.
SUB-PHYLA VERTEBRATA :
- Have notochord only during embryonic period.
- Notochord gets replaced by bony or cartilaginous vertebral column.
- Have ventral muscular heart with two, three or four chambered.
- Paired appendages which may be fins or limbs.
- Kidneys for excretion and osmoregulation.
Division Agnatha (lack jaws) -
Class: Cyclostomata :
- Have sucking and circular mouth without jaws.
- Live as ectoparasites on some fishes.
- Devoid of scales, no paired fins.
- Cranium and vertebral column is cartilaginous.
- Marine habit but migrates to fresh water for spawning and die after spawning.
- Larva returns to ocean after metamorphosis.
e.g., Petromyzon.
Division Gnathostomata (Bear Jaws) -
SUPER-CLASS: PISCES -
Class 1: Chondrichthyes :
- Have cartilaginous endoskeleton.
- Mouth ventrally located.
- Notochord persists throughout life.
- Gill slits are separate and without operculum.
- Skin has placoid scales.
- Jaw contains teeth, which are modified placoid scales.
- Mostly predaceous.
- Swim bladder absent.
- Heart is two chambered. (one auricle and one ventricle)
- Some of them contain electric organs ( e.g. Torpedo)
- Some possesses poison sting. ( e.g. Trygon)
- Poikilotherm or cold blooded.
- Dioecious.
- Sexually dimorphic, male’s pelvic fin bears claspers.
- Fertilization internal.
- Many of them viviparous.
e.g., Torpedo, Trygon, Scoliodon.
Class 2 : Osteichthyes :
- Includes both marine and fresh water fishes.
- Bony endoskeleton.
- Mouth is usually terminal.
- Four pairs of gill slits covered by operculum.
- Skin has cycloid/ctenoid scales.
- Air bladder is present for buoyancy.
- Heart is two chambered.
- Cold blooded animals.
- Dioecious.
- Sexually monomorphic.
- Fertilization external.
- Mostly oviparous
- Development is indirect.
e.g., Hippocampus, Labeo, Catla, Betta.
