Biology: Animal Kingdom

• Animals are classified on the basis of common fundamental features like the cellular arrangement, symmetry of the body, presence or absence of the coelom, specific features of the digestive, circulatory and reproductive system
• Cellular level of organisation: cells arranged as loose aggregates, present in Porifera (sponges)
• Tissue level of organisation: cells performing the same function form tissues, present in coelenterates
• Organ level of organisation: tissues grouped together to form an organ, which performs particular function, e.g. Platyhelminthes
• Organ system level of organisation: afew organs coordinatively perform a certain physiological function, e.g. Annelids, Arthropods, Molluscs, Echinoderms and Chordates
• Open circulatory system: cells and tissue directly receive the blood pumping out of the heart
• Closed circulatory system: blood is circulated through arteries, veins and capillaries
• Diploblastic: embryo with two germinal layers called external ectoderm and internal endoderm, e.g. Porifera, Cnidaria
• Triploblastic: embryo with three germinal layers, mesoderm between ectoderm and endoderm, e.g. Platyhelminthes to Chordates
• Asymmetrical: no line of symmetry in the body, e.g. sponges
• Radial symmetry: any plane passing through centre divides the body in two symmetrical halves, e.g. coelenterates, ctenophores
• Bilateral symmetry: a plane divides the body in symmetrical left and right halves, e.g. annelids, arthropods, etc.

·       Echinoderms exhibit radial as well as bilateral symmetry at different stages of their life

• Body cavity between the body wall and gut wall, lined by mesoderm is called coelom
• Acoelomates: body cavity is absent, e.g. Platyhelminthes
• Pseudocoelomates: mesoderm is present as scattered pouches, e.g. Aschelminthes

Coelomates: having coelom (body cavity) e.g. from Annelida to Chordata

• Earthworm’s body shows metameric segmentation
• Animals with notochord are called chordates, animals without notochord are called non-chordates, e.g. Porifera to Echinodermata.

1.     Phylum – Porifera (Sponges)

·       Marine, asymmetrical with the cellular level of organisation

·       Food intake, gaseous exchange and excretion occurs through the water transport system

·       Water enters through pores called Ostia and goes out through osculum via central cavity known as spongocoel

·       Spongocoel is lined by collar cells or choanocytes

·       Intracellular digestion

·       Body skeleton is made up of spongin fibres or spicules

·       Sponges are hermaphrodite

·       Reproduce asexually by fragmentation and sexually by the formation of gametes

·       Fertilisation is internal and the development of zygote goes through a distinct larval stage

·       Examples: Spongilla (freshwater sponge), Euspongia (bath sponge), Sycon,

2.     Phylum – Coelenterata (cnidaria)

·       Aquatic, sessile or free-swimming, tissue level of organisation, diploblastic and radially symmetrical and acoelomate

·       The central gastro-vascular cavity has a single opening called hypostome, which is surrounded by sensory tentacles

·       Cnidoblasts are present on the tentacles, which contain nematocysts

·       Digestion is extracellular and intracellular

·       Corals have calcium carbonate skeleton

·       A polyp is a sessile and cylindrical form, e.g Hydra, Adamsia

·       Medusa is an umbrella-shaped free-swimming form, e.g. Aurelia (jellyfish)

·       In some coelenterates, e.g. Obelia alternation of generation (metagenesis) exist. Polyp form produces medusae asexually and medusae produce polyp sexually

Examples: Meandrina (Brain coral), Adamsia (Sea anemone), Gorgonia (Sea-fan), Physalia (Portuguese man of war)

3.     Phylum – Ctenophora (sea walnuts or comb jellies)

·       Marine, tissue level of organisation, diploblastic and radially symmetrical and acoelomate

·       Eight rows of ciliated comb plates present externally

·       Digestion is extracellular and intracellular

·       Bioluminescence is present

·       Hermaphrodite

·       Sexual reproduction, fertilisation is external with indirect development

·       Examples: Ctenoplana, Pleurobrachia

4.     Phylum – Platyhelminthes (flatworms)

·       Mostly endoparasites, dorsoventrally flattened body, triploblastic, bilaterally symmetrical, acoelomate with organ level of organisation

·       Hooks and suckers are present in parasites

·       Flame cells are present, which help in osmoregulation and excretion

·       Hermaphrodite or monoecious

·       Internal fertilisation and indirect development through many larval stages

·       Planaria can regenerate

·       Examples: Fasciola (Liver fluke), Taenia (tapeworm)

5.     Phylum – Aschelminthes

·       Free-living or parasitic, aquatic or terrestrial

·       Round body in cross-section, bilaterally symmetrical, triploblastic, pseudocoelomate with organ system organisation

·       The alimentary canal is complete and has a muscular pharynx

·       Dioecious, females are longer than males

·       Internal fertilisation with direct or indirect development

Examples: Ascaris (roundworm), Wuchereria (Filarial worm), Ancylostoma (hookworm)

1.     Phylum – Annelida

·       Bilaterally symmetrical, triploblastic, coelomate, organ system organisation

·       Metamerically segmented

·       Longitudinal and circular muscles help in locomotion

·       Nereis, an aquatic animal has appendages called parapodia, which help in swimming

·       Closed circulatory system

·       Nephridia is present for osmoregulation and excretion

·       Paired ganglia are present, which are connected to double ventral nerve cord by lateral nerves

·       Reproduction is sexual. Nereis is dioecious, earthworm and leeches are monoecious

Examples: Pheretima (earthworm), Nereis, Hirudinaria (bloodsucking leech)

Phylum – Arthropoda

·       Largest phylum with two-thirds of all known animals

·       It contains insects

·       Bilaterally symmetrical, triploblastic, coelomate, organ system organisation

·       Their body is covered by chitinous exoskeleton

·       The characteristic property of the group is jointed legs

·       Their body can be divided into three regions; head, thorax and abdomen

·       Respiration is by trachea, gills, book gills, book lungs

·       The circulatory system is open type

·       Statocyst or balancing organs are present

·       Eyes are simple or compound

·       Malpighian tubules help in excretion

·       Mostly dioecious, oviparous and fertilisation is internal

·       Examples: economically important species- Bombyx (silkworm), Apis (honey bee) Vector for diseases- mosquitoes like Anopheles, Aedes, Culex.Living fossil- Limulus (King crab)

1.      Phylum – Mollusca

·       Bilaterally symmetrical, triploblastic, coelomate, organ system organisation

·       Unsegmented body covered with a calcareous shell

·       Distinct head, muscular foot and the visceral hump is present

·       Respiratory and excretory functions are executed by feather-like gills

·       The radula is a rasping organ for feeding

·       They are dioecious, oviparous with indirect development

Examples: Pila (apple snail), Octopus (devilfish), Loligo (squid), Sepia (cuttlefish), Pinctada (pearl oyster)

1.     Phylum – Echinodermata

·       Adult- radially symmetrical, larvae- bilaterally symmetrical

·       Triploblastic and coelomate

·       Endoskeleton of calcareous ossicles

·       The mouth is present on the ventral side and anus on the dorsal side

·       The characteristic feature is the presence of Water vascular system, which helps in feeding, locomotion and respiration

·       Dioecious, external fertilisation with indirect development

·       Examples: Asterias (starfish), Ophiura (brittle star), Antedon (sea lily), Echinus (sea urchin)

1.     Phylum – Hemichordata

·       Presence of stomochord, a structure similar to the notochord

·       Bilaterally symmetrical, triploblastic, coelomate, organ system organisation

·       Cylindrical body with a proboscis, a collar and a long trunk

·       Gills are present and circulation is open type

·       Proboscis gland works as an excretory organ

·       Dioecious, external fertilisation with indirect development

·       Examples: Balanoglossus, Saccoglossus