Key Notes: Animal Kingdom- 2 | Additional Study Material for NEET PDF Download

1. Phylum – Chordata

• Fundamentally characterised by the presence of
  (i) a notochord,
  (ii) a dorsal hollow nerve cord and
  (iii) paired pharyngeal gill slits

Chordata

• Bilaterally symmetrical,
• Triploblastic,
• Coelomate
• Organ-system level of organisation.
• Possess a post anal tail
• Closed circulatory system.

2. Phylum Chordata is divided into three subphyla

• Urochordata or Tunicata,
• Cephalochordata
• Vertebrata.

3. Subphyla Urochordata + Cephalochordata → Protochordates

• Exclusively marine.

4. In Urochordata

Notochord is present only in larval tail

• Examples: Urochordata – Ascidia, Salpa, Doliolum;

5. In Cephalochordata

Notochord extends from head to tail region and is persistent throughout their life.

• Examples: Cephalochordata – Branchiostoma (Amphioxus or Lancelet).

6. The members of subphylum Vertebrata

• Possess notochord during the embryonic period.
• The notochord is replaced by a cartilaginous or bony vertebral column in the adult.
• “all vertebrates are chordates but all chordates are not vertebrates”
• Besides the basic chordate characters,
  (i) vertebrates have a ventral muscular heart with two, three or four chambers,
  (ii) kidneys for excretion and osmoregulation and
  (iii) paired appendages which may be fins or limbs.

7. Class – Cyclostomata

• All are ectoparasites on some fishes.
• Elongated body bearing 6-15 pairs of gill slits for respiration.
• Cyclostomes have a sucking and circular mouth without jaws
• 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).

8. Class – Chondrichthyes

• Marine animals
• Streamlined body
• Cartilaginous endoskeleton
• 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.
• 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 claspers.
• They have internal fertilisation and many of them are viviparous
• Examples:
  (i) Scoliodon (Dog fish),
  (ii) Pristis (Saw fish),
  (iii) Carcharodon (Great white shark),
  (iv) Trygon (Sting ray).

9. Class – Osteichthyes

• both marine and fresh water fishes
• Bony endoskeleton.
• Streamlined Body.
• Mostly terminal mouth
• Four pairs of gills ; covered by an operculum on each side.
• Skin is covered with cycloid/ctenoid scales.
• Air bladder is present which regulates buoyancy.
• Heart is two chambered (one auricle and one ventricle).
• They are cold-blooded animals.
• Sexes are separate.
• Fertilisation is usually external.
• They are mostly oviparous and development is direct.
• Examples:
  (i) Marine – Exocoetus (Flying fish), Hippocampus (Sea horse);
  (ii) Freshwater – Labeo (Rohu), Catla (Katla), Clarias (Magur);
  (iii) Aquarium – Betta (Fighting fish), Pterophyllum (Angel fish).

10. Class – Amphibia (Gr., Amphi : dual, bios, life)

• Live in aquatic as well as terrestrial habitats
• Most of them have two pairs of limbs.
• Body is divisible into head and trunk.
• Tail may be present in some.
• The amphibian skin is moist (without scales).
• The eyes have eyelids.
• A tympanum represents the ear.
• Alimentary canal, urinary and reproductive tracts open into a common chamber called cloaca which opens to the exterior.
• Respiration is by gills, lungs and through skin.
• The heart is three chambered (two auricles and one ventricle).
• These are cold-blooded animals.
• Sexes are separate.
• Fertilisation is external.
• They are oviparous and development is indirect.
• Examples:
  (i) Bufo (Toad),
  (ii) Rana (Frog),
  (iii) Hyla (Tree frog),
  (iv) Salamandra (Salamander),
  (v) Ichthyophis (Limbless amphibia)

11. Class – Reptilia

• Creeping or crawling mode of locomotion (Latin, reptum, to creep or crawl).
• Mostly terrestrial animals
• Body is covered by dry and cornified skin, epidermal scales or scutes
• Do not have external ear openings.
• Tympanum represents ear.
• Limbs, when present, are two pairs.
• Heart is usually three-chambered, but four-chambered in crocodiles.
• Reptiles are poikilotherms.
• Snakes and lizards shed their scales as skin cast.
• Sexes are separate.
• Fertilisation is internal.
• They are oviparous and development is direct.
• Examples:
  (i) Chelone (Turtle),
  (ii) Testudo (Tortoise),
  (iii) Chameleon (Tree lizard),
  (iv) Calotes (Garden lizard),
  (v) Crocodilus (Crocodile),
  (vi) Alligator (Alligator).
  (vii) Hemidactylus (Wall lizard),
  (viii) Poisonous snakes
  – Naja (Cobra), Bangarus (Krait), Vipera (Viper). 

12. Class – Aves

• The characteristic features → Presence of feathers 
• Most of them can fly except flightless birds (e.g., Ostrich).
• They possess beak
• The forelimbs are modified into wings.
• The hind limbs generally have scales and are modified for walking, swimming or clasping the tree branches.
• Skin is dry without glands except the oil gland at the base of the tail.
• Endoskeleton is fully ossified (bony)
• Long bones are hollow with air cavities (pneumatic).
• The digestive tract of birds has additional chambers, the crop and gizzard.
• Heart is completely four chambered.
• They are warm-blooded (homoiothermous) animals, i.e., they are able to maintain a constant body temperature.
• Respiration is by lungs.
• Air sacs connected to lungs supplement respiration.
• Sexes are separate.
• Fertilisation is internal.
• They are oviparous and development is direct.
• Examples:
  (i) Corvus (Crow),
  (ii) Columba (Pigeon),
  (iii) Psittacula (Parrot),
  (iv) Struthio (Ostrich),
  (v) Pavo (Peacock),
  (vi) Aptenodytes (Penguin),
  (vii) Neophron (Vulture).

13. Class – Mammalia

• Found in a variety of habitats – polar ice caps, deserts, mountains, forests, grasslands and dark caves.
• Adapted to fly or live in water.
• The most unique mammalian characteristic is the presence of milk producing glands (mammary glands) by which the young ones are nourished.
• They have two pairs of limbs, adapted for walking, running, climbing, burrowing, swimming or flying
• The skin of mammals is unique in possessing hair.
• External ears or pinnae are present.
• Different types of teeth are present in the jaw.
• Heart is four chambered.
• They are homoiothermous.
• Respiration is by lungs.
• Sexes are separate
• Fertilisation is internal.
• They are viviparous with few exceptions
• Development is direct. 
• Examples:
  (i) Oviparous
  - Ornithorhynchus (Platypus);
  (ii) Viviparous
  - Macropus (Kangaroo),
  - Pteropus (Flying fox),
  - Camelus (Camel),
  - Macaca (Monkey),
  - Rattus (Rat),
  - Canis (Dog),
  - Felis (Cat),
  - Elephas (Elephant),
  - Equus (Horse),
  - Delphinus (Common dolphin),
  - Balaenoptera (Blue whale),
  - Panthera tigris (Tiger),
  - Panthera leo (Lion)