Animal Kingdom Biology Notes - Basis of Classification, Non-Chordates, Chordates Phylum and Classes with Examples

• Animals are multicellular and heterotrophic organisms without cell wall and chlorophyll.
• Kingdom Animalia includes 11 major phyla:

1. Porifera

2. Cnidaria

3. Ctenophora

4. Platyhelminthes

5. Aschelminthes

6. Annelida

7. Arthropoda

8. Mollusca

9. Echinodermata

10. Hemichordata

11. Chordata

Basis of Classification

1. Levels of Organization

• Based on this, animals are grouped into four levels:
•  
• Cellular level of organization: Here, the cells are arranged as loose cell aggregates. E.g. Porifera.
• Tissue level of organization: Here, the cells are arranged into tissues. E.g. Cnidarians and Ctenophores.
• Organ level of organization: Here, tissues are arranged into organs. E.g. Platyhelminthes and other higher phyla.
• Organ system level of organization: Here, organs are associated to organ system. Each system performs a specific physiological function. E.g. Higher animals.

Organ systems of various animals show complexities. E.g.

• Digestive system is 2 types:
• Incomplete: It has only a single opening that acts as mouth & anus. Seen in Cnidaria and Platyhelminthes.
• Complete: It has 2 openings (mouth & anus).
• Circulatory system is 2 types: open & closed.

2. Body Symmetry

• It is the arrangement of similar body parts on 2 sides of main axis of the body. So, body can be divided into 2 equal halves.
• Based on symmetry, animals are 3 types:
• Asymmetrical: Here, body cannot be divided into 2 equal halves. E.g. Most Poriferans, Snails etc.
• Radial symmetry: Here, body can be divided into 2 equal halves in any vertical plane along central axis (oral-aboral axis) of the body. E.g. some Poriferans, Cnidarians, Ctenophores and Echinoderms (adult).
• Bilateral symmetry: Here, body can be divided into equal right & left halves in only one plane. E.g. Platyhelminthes to Chordata (except adult Echinodermata).

3. Germinal Layers (Embryonic Layers)

• These are layers of embryo from which all the body organs are formed.
• Based on the number of germ layers, animals are 2 types - Diploblastic and Triploblastic.
• Diploblastic animals: 2 germ layers - outer ectoderm and inner endoderm. In between these layers, an undifferentiated jelly-like layer called mesoglea is present. E.g. Cnidaria & Ctenophora.
• Triploblastic animals: 3 germ layers - Outer ectoderm, middle mesoderm and inner endoderm. E.g. Platyhelminthes to Chordata.

4. Coelom (Body Cavity)

• It is the cavity lined by mesoderm.
• It is seen between body wall and gut wall.
• Coelom separates the muscles of gut and body wall.
• Based on the nature of coelom, animals are 3 types:
• Acoelomate: No coelom. The space between body wall and digestive cavity is filled with matrix (parenchyma). E.g. Porifera to Platyhelminthes.
• Pseudocoelomate: False coelom. Here, the body cavity is not lined by mesoderm. Mesoderm is scattered pouches. E.g. Aschelminthes.
• Coelomate: True coelom. Here, the coelom arises from the mesoderm. E.g. Annelida to Chordata.

5. Metamerism (Segmentation)

• It is the phenomenon in which the body or organs is externally and internally divided into repeated segments (metameres).
• E.g. Annelids (earthworm etc.), Arthropods.

6. Notochord

• It is a mesodermally derived supporting rod formed on the dorsal side during embryonic development in some animals.
• Animals with notochord are called chordates and those without notochord are called non-chordates.

Phylum Porifera (Sponges): General Characters

• Grades of Organization: Cellular grade.
• Symmetry: Asymmetrical. Some are radial.
• Coelom: Acoelomate
• Habit and Habitat: Aquatic (mostly marine). Sedentary. Solitary/colonial.
• Digestive System: Absent. Intracellular digestion.
• Respiratory System: Absent
• Circulatory System: Absent
• Reproduction:
• Asexual (fragmentation) & Sexual.
• Hermaphrodite (Monoecious): Male and female sex organs are seen in same individual.
• Internal fertilization.
• Development is indirect.
• Unique Features:
• Water canal (water transport) system. Millions of ostia (pores).
• Water canal system: Here, water enters through minute pores (ostia) in the body wall into a central cavity (spongocoel), from where it goes out through osculum. Canal system is used for food gathering, gas exchange and removal of wastes.
• Spongocoel & canals are lined with choanocytes (collar cells).
• Body is supported by spicules and spongin fibres.
• Examples:
• Sycon (Scypha)
• Spongilla (fresh water sponge)
• Euspongia (Bath sponge)

Phylum Cnidaria (Coelenterata): General Characters

• Grades of Organization: Tissue grade.
• Symmetry: Radial symmetry.
• Germ Layers: Diploblastic
• Coelom: Acoelomate
• Habit and Habitat:
• Aquatic (mostly marine).
• Sessile/free swimming.
• Solitary/colonial.
• Digestive System:
• Incomplete.
• Intracellular & extracellular digestion.
• Respiratory System: Absent
• Circulatory System: Absent
• Reproduction:
• Polyp reproduces asexually (budding) and medusa sexually.
• Most are separate sexes.
• External fertilization.
• Development is indirect.
• Unique Features:
• Tentacles with cnidoblasts.
• Tentacles: Finger-like structures which surround the mouth of coelenterates. Used for food capture & defense.
• Cnidoblasts (Cnidocytes): These are stinging cells (present on the tentacles and the body) with a poison-filled capsule called nematocyst. Cnidoblast is used for anchorage, defense and to capture prey.

• Gastro-vascular cavity (coelenteron) with an opening (mouth) on hypostome.
• Polyp & Medusa: 2 types of body forms in cnidarians.
• Polyp is cylindrical sessile form. E.g. Hydra, Adamsia.
• Medusa is umbrella-like, free-swimming form. E.g. Aurelia (Jelly fish).

• Some show alternation of generation (Metagenesis). It is the phenomenon in which polyps produce medusae asexually and medusae form the polyps sexually. E.g. Obelia.
• Corals have skeleton (CaCO₃).
• Examples:
• Hydra
• Obelia
• Aurelia
• Physalia (Portuguese man of war)
• Adamsia (Sea-anemone)
• Pennatula (Sea pen)
• Gorgonia (Sea fan)
• Meandrina (Brain coral)

Phylum Ctenophora (Comb Jellies): General Characters

• Grades of Organization: Tissue grade.
• Symmetry: Radial symmetry.
• Germ Layers: Diploblastic
• Coelom: Acoelomate
• Habit and Habitat:
• Exclusively marine.
• Solitary & pelagic
• Digestive System:
• Incomplete.
• Intracellular & extracellular digestion.
• Respiratory System: Absent
• Circulatory System: Absent
• Reproduction:
• Only Sexual.
• Hermaphrodite.
• External fertilization.
• Development is indirect.
• Unique Features:
• Locomotion is by 8 vertical external rows of ciliated comb plates.
• Tentacles present.
• Shows Bioluminescence (property to emit light from the body).
• Examples:
• Ctenoplana
• Pleurobrachia

Phylum Platyhelminthes (Flatworms): General Characters

• Grades of Organization: Organ & Organ system.
• Symmetry: Bilateral symmetry.
• Germ Layers: Triploblastic.
• Coelom: Acoelomate
• Habit and Habitat: Mainly aquatic. Endoparasites. Some are free-living.
• Digestive System: Incomplete.
• Respiratory System: Absent
• Circulatory System: Absent
• Reproduction:
• Asexual (fragmentation) and Sexual.
• Hermaphrodite.
• Internal Fertilization.
• Development is indirect.
• Many larval stages.
• Unique Features:
• Unsegmented, dorso-ventrally flattened body (except tape worms).
• Excretion and osmo-regulation by Flame cells.
• Parasites have Hooks & suckers.
• Some absorb nutrients from the host through their body surface.

• Examples:
• Taenia solium (Tape worm)
• Fasciola (Liver fluke)
• Planaria (shows high regeneration capacity).

Phylum Aschelminthes (Roundworms): General Characters

• Grades of Organization: Organ system.
• Symmetry: Bilateral symmetry.
• Germ Layers: Triploblastic.
• Coelom: Pseudocoelomate.
• Habit and Habitat: Aquatic and terrestrial. Free living or parasitic in plants & animals.
• Digestive System: Complete. Tubular alimentary canal with well-developed muscular pharynx.
• Respiratory System: Absent
• Circulatory System: Absent
• Reproduction:
• Dioecious (Sexes are separate).
• Sexual reproduction.
• Internal fertilization.
• Development is direct or indirect.
• Unique Features:
• Body is circular in cross section.
• An excretory tube to remove body waste through excretory pore.
• Male and female are distinct. Females are longer than males.
• Examples:
• Ascaris (Roundworm)
• Ancylostoma (Hookworm)
• Wuchereria (Filarial worm).

Phylum Annelida (Segmented / Ringed Worms): General Characters

• Grades of Organization: Organ system.
• Symmetry: Bilateral symmetry.
• Germ Layers: Triploblastic.
• Coelom: Coelomate.
• Habit and Habitat: Terrestrial, fresh water or marine. Free living or parasitic.
• Digestive System: Complete.
• Respiratory System: Cutaneous respiration. Some have branchial (gill) respiration.
• Circulatory System: Closed type.
• Reproduction:
• Sexual.
• Earthworms & leeches are monoecious.
• Neries is dioecious.
• Development is direct or indirect.
• Unique Features:
• Segmentation like rings.
• Longitudinal and circular muscles help in locomotion.
• Locomotory organs are setae (in earthworm) or parapodia (in Neries).
• Excretion by Nephridia.
• Paired ganglia connected by lateral nerves to a double ventral nerve cord.
• Examples:
• Pheretima (earthworm)
• Hirudinaria (blood sucking Leech)
• Neries (aquatic. Parapodia for swimming).

Phylum Arthropoda (Joint-Legged Animals): General Characters

Arthropoda is the largest phylum. Over two-thirds of all named species are arthropods.

• Grades of Organization: Organ system.
• Symmetry: Bilateral symmetry.
• Germ Layers: Triploblastic.
• Coelom: Coelomate.
• Habit and Habitat: Cosmopolitan.
• Digestive System: Complete.
• Respiratory System: Gills/book gills/trachea/book lungs.
• Circulatory System: Open type.
• Reproduction:
• Mostly dioecious.
• Usually internal fertilization.
• Mostly oviparous.
• Development is direct or indirect.
• Unique Features:
• Jointed appendages.
• Body has 3 regions: head, thorax & abdomen.
• Body is covered by chitinous cuticle (exoskeleton).
• Excretion by Malpighian tubules.
• Sensory organs are antennae, compound & simple eyes, statocysts (balance organs).
• Examples:
• Spider, Scorpion, Crab, Prawn, Insects etc.
• Economically important insects: Apis, Bombyx, Laccifer.
• Vectors: Mosquitoes (Anopheles, Culex & Aedes), Housefly etc.
• Gregarious pest: Locusta.
• Living fossil: Limulus (King crab).

Phylum Mollusca (Soft Bodied Animals): General Characters

Mollusca is the second largest phylum.

• Grades of Organization: Organ system.
• Symmetry: Bilateral symmetry.
• Germ Layers: Triploblastic.
• Coelom: Coelomate.
• Habit and Habitat:
• Aquatic.
• Few are terrestrial.
• Digestive System: Complete.
• Respiratory System: Gills in aquatic forms and pulmonary sac in terrestrial forms.
• Circulatory System: Open type.
• Reproduction:
• Dioecious.
• Oviparous.
• Development is direct or indirect.
• Unique Features:
• Body has head, visceral hump & muscular foot.
• Head has sensory tentacles.
• Calcareous shell.
• Mantle: The membrane which covers visceral mass.
• Space between the hump and mantle is called mantle cavity. It contains feather-like gills for respiration & excretion.
• Radula: File-like rasping organ present in the mouth. It is used for feeding.
• Examples:
• Pila (Apple Snail)
• Pinctada (Pearl Oyster)
• Sepia (Cuttlefish)
• Loligo (Squid)
• Octopus (Devil fish)
• Aplysia (Sea Hare)
• Dentalium (Tusk shell)
• Chaetopleura (Chiton)

Phylum Echinodermata (Spiny Skinned Animals): General Characters

• Grades of Organization: Organ system.
• Symmetry: Adults radial. Larvae bilateral.
• Germ Layers: Triploblastic.
• Coelom: Coelomate.
• Habit and Habitat: Exclusively marine.
• Digestive System:
• Complete.
• Ventral mouth and dorsal anus.
• Respiratory System: Skin gills. Water vascular system.
• Circulatory System: Open type.
• Reproduction:
• Dioecious.
• External fertilization.
• Development is indirect.
• Ciliated free-swimming larva.
• Unique Features:
• They have an endoskeleton of calcareous ossicles (Spiny bodied).
• Head absent.
• Water vascular system for locomotion, respiration, capture & transport of food.
• Excretory system absent.
• Examples:
• Asterias (Starfish)
• Echinus (Sea Urchin)
• Echinocardium
• Antedon (Sea Lily)
• Cucumaria (Sea Cucumber)
• Ophiura (Brittle Star)

Phylum Hemichordata: General Characters

Hemichordata was earlier considered as a sub-phylum of Chordata. Like chordates, it has pharyngeal gill slits.

• Grades of Organization: Organ system.
• Symmetry: Bilateral.
• Germ Layers: Triploblastic.
• Coelom: Coelomate.
• Habit and Habitat: Exclusively marine.
• Digestive System: Complete.
• Respiratory System: Gills.
• Circulatory System: Open type.
• Reproduction:
• Dioecious.
• External fertilization.
• Development is indirect.
• Unique Features:
• Worm-like cylindrical body formed of anterior proboscis, a collar and a long trunk.
• Collar bears stomochord (a rudimentary structure similar to notochord).
• Excretion by Proboscis gland.
• Examples:
• Balanoglossus (Tongue worm)
• Saccoglossus

Phylum Chordata

It includes animals with notochord, dorsal tubular nerve cord, and pharyngeal gill slits.

Notochord is a flexible rod located in the mid-dorsal line between the alimentary canal and the nerve cord in the embryo.

Differences between Chordata and Non-Chordata

Phylum Chordata is classified into 3 subphyla: Urochordata, Cephalochordata, and Vertebrata.

Protochordata (Acraniata)

Urochordata (Tunicata)

• Notochord is present only in larval tail.
• Exclusively marine.
• Hermaphrodite.
• E.g., Ascidia, Salpa, Doliolum

Cephalochordata

• Notochord from head to tail region and is persistent throughout the life.
• Fish-like body.
• Exclusively marine.
• Sexes are separate.
• E.g., Branchiostoma (Amphioxus or Lancelet)

Ascidia

Vertebrata (Craniata)

• Possess notochord during the embryonic period.
• Notochord is replaced by a cartilaginous or bony vertebral column in the adult.
• Ventral muscular heart.
• Kidneys for excretion and osmoregulation.
• Paired appendages (fins or limbs).

Classification of Vertebrata

Class Cyclostomata

• All are ectoparasites on some fishes.
• Elongated body without scales and paired fins.
• 6-15 pairs of gill slits for respiration.
• Sucking and circular mouth without jaws.
• Cartilaginous cranium and vertebral column.
• Circulation is closed type.
• Marine, but migrate for spawning to fresh water. After spawning, they die. Their larvae, after metamorphosis, return to ocean.
• E.g., Petromyzon (Lamprey), Myxine (Hagfish)

Superclass Pisces (Fishes)

Class Chondrichthyes (Cartilaginous Fishes)

• Marine. Stream-lined body. Predaceous.
• Cartilaginous endoskeleton.
• Notochord is persistent throughout life.
• Ventral mouth.
• Gill slits without operculum. Powerful jaws.
• Skin with placoid scales. Teeth are modified placoid scales which are backwardly directed.
• No air bladder. So, they have to swim constantly to avoid sinking.
• Poikilotherms (Cold-blooded animals): Animals that lack the capacity to regulate their body temperature.
• Two-chambered heart (one auricle and one ventricle).
• Sexes are separate. In males, pelvic fins bear claspers. Internal fertilization. Many of them viviparous.
• Examples:
• Scoliodon (Dogfish)
• Pristis (Saw Fish)
• Carcharodon (Great White Shark)
• Trygon (Sting Ray - has poison sting)
• Torpedo (Electric Ray - has electric organ)

Class Osteichthyes (Bony Fishes)

• Marine & fresh water. Stream-lined body.
• Bony endoskeleton.
• Terminal mouth.
• 4 pairs of gills covered by operculum on each side.
• Scales are cycloid, ctenoid, etc.
• Air bladder for buoyancy.
• Poikilotherms (cold-blooded).
• Two-chambered heart (one auricle and one ventricle).
• Sexes are separate. External fertilisation.
• Mostly oviparous. Development is direct.
• Examples:
• Marine: Exocoetus (Flying Fish), Hippocampus (Seahorse)
• Fresh Water: Labeo (Rohu), Catla (Katla), Clarias (Magur)
• Aquarium: Betta (Fighting Fish), Pterophyllum (Angel Fish)

Superclass Tetrapoda

Class Amphibia

• They live in aquatic & terrestrial habitats and need water for breeding.
• Body has head & trunk. Some have tail.
• Moist skin without scales. Most have 2 pairs of limbs.
• Tympanum represents ear.
• 3-chambered heart (2 auricles + 1 ventricle).
• Poikilotherms (Cold-blooded animals): Animals that lack the capacity to regulate their body temperature.
• Alimentary canal, urinary & reproductive tracts open into a Cloaca which opens to exterior.
• Respiration is by gills (in larva), lungs & skin.
• Sexes are separate. External fertilisation. Oviparous.
• Development is indirect.
• Examples:
• Bufo (Toad)
• Rana (Frog)
• Hyla (Tree frog)
• Salamandra (Salamander)
• Ichthyophis (Limbless amphibia)

Class Reptilia

• Dry & cornified skin, epidermal scales or scutes.
• Snakes and lizards shed their scales as skin cast.
• Limbs - 2 pairs (if present).
• Crawling mode of locomotion.
• Tympanum represents ear.
• 3-chambered heart (4-chambered in crocodiles).
• Poikilotherms.
• Well-developed alimentary canal.
• Respiration by lungs.
• Internal fertilisation. Oviparous.
• Development is direct.
• Examples:
• Chelone (Turtle)
• Testudo (Tortoise)
• Chameleon (Tree lizard)
• Calotes (Garden lizard)
• Crocodilus (Crocodile)
• Alligator
• Hemidactylus (Wall lizard)
• Poisonous snakes: Naja (Cobra), Bangarus (Krait), Vipera (Viper) etc.
• Non-poisonous snakes: Python etc.

Class Aves (Birds)

• Presence of feathers and beak. Forelimbs are modified into wings.
• Dry skin without glands except the oil gland at the base of tail.
• Hind limbs have scales and are modified for walking, swimming or clasping tree branches.
• Hollow & pneumatic long bones.
• Tympanum represents ear.
• 4-chambered heart.
• Homoiotherms (warm-blooded animals): Animals having ability to maintain a constant body temperature.
• Digestive tract has additional chambers, the crop & gizzard.
• Double respiration.
• Air sacs connected to lungs.
• Internal fertilisation.
• Oviparous.
• Development is direct.
• Examples:
• Corvus (Crow)
• Columba (Pigeon)
• Psittacula (Parrot)
• Struthio (Ostrich)
• Pavo (Peacock)
• Aptenodytes (Penguin)
• Neophron (Vulture) etc.

Class Mammalia

• Presence of mammary glands (milk producing glands).
• Skin with hair.
• 2 pairs of limbs for walking, running, climbing, burrowing, swimming or flying.
• External ear (Pinnae).
• 4-chambered heart.
• Homoiotherms.
• Well-developed alimentary canal.
• Dentition is Heterodont, thecodont & diphyodont.
• Respiration by lungs.
• Sexes are separate.
• Internal fertilisation.
• Viviparous (except Echidna and Platypus).
• Development is direct.
• Examples:
• Ornithorhynchus (Platypus)
• 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)