Animal Kingdom

Non-chordates up to phyla level

  • Phylum - Porifera : Most poriferans are marine and remain attached to rocks (sessle). A few poriforans lives in fresh water (eg : spongilla). These are most primitive of multi cellular animals called sponges (@ pore bearers). Study about sponges is known as parazoology.
  • The body wall of common sponges have three body layers namely pinacoderm (dermal layer), choanoderm (gastral layer) and mesohyl layer (mesenchyme).
  • Archaeocytes are modified amoebocytes and they may be converted into another types of cells, so it is called as "totipotent" cells. The central body cavity of a sponge is called spongocoel / paragastric cavity.
  • The body of sponge is organized as canals or a complex system of pores which are called as canal system.
  • The main function of canal system is continuous transport of water, thus it helps to sponges in nutrition, respiration excretion and reproduction.
  • The skeleton of sponges consist of calcaneus / siliceous spicules (or) fine spongin fibres (or) both symmetry radial (or) no symmetry.
  • Digestion is intracellular and occurs in food valvoles as in protozoans. Exchange of gases occurs by diffusion through the plasma membranes of the cells.
  • Choanoderm is mainly made of choanocytes. The cells (choanocytes) are characteristics of poriferans. Cells are loosely arranged and donor from definite layers, hence not regarded truly diploblastic.
  • Excretion : Removal of metabolic wastes occurs by diffusion through cell membrane (Ammonia is chief excretory waste).
  • All sponges are hermaphrodite but cross fertilization is the rule. A sexual reproduction occurs by budding / gemmules. sexual reproduction occurs by ova and sperms.
  • In fresh water sponges and a few marine sponges, gemmules (internal buds) are formed each gemmule has a mass of archaeocytes surrounded by protecting cover.
  • Gemmule formation is called internal budding sponges have a great power of regeneration.
  • Development of sponges are indirect and includes free swimming larvae, amphiblastula (in sycon) or parenchymula (in leucosolenia) for dispersal of the species.
  • Examples :-
    (1) Sycon (Scypha)
    (2) Spongilla (fresh water sponges)
    (3) Euspongia (Bath Sponge)


  • All are aquatic, mostly marine, sessile / free swimming, diploblastic, radially symmetrical animals. They named so, because they derived from cnidoblasts / cnidocytes.
  • Body organization is tissue level. They exhibit a blind sac body plan & radially symmetric. Body consists of endoderm & ectoderm which are separated by jelly like mesoglea. So they are diploblastic. They are Acoelomates
  • Most ectodermal cells are contractile and posses muscle fibres within them. Few transmit stimuli and are connected to form a nerve net.
  • Digestion is intracellular and also extracellular hydra feeds only the substance with glutathione.
  • Stinging cells (or) cnidoblast are the ectoderm of the tentacles. Stinging cell organelles (or) nematocysts serve for adhesion, food capture offense and defense.
  • (i) Penetrant (largest) → hypnotoxin to paralyze the prey
    (ii) Desmosomes (smallest) → their tube coils around prey
    These are types of cnidoblasts. Large and small glutinants secrete sticky substance to help in locomotion.
  • Cnidarians exist in both forms exhibit alteration of generation (metagenesis). Polyp produce medusae asexually and medusae form the polyps sexually (eg : obelia).
  • Polyp is sessile, the body is hydra like structure. They are cylindrical stalk with mouth and tentacles facing upwards. Medusa is free floating / swimming structure like jelly fish. It is a bell / umbrella like structure with mouth and tentacles facing downwards.
  • Interstitial cells in the body wall of coelenterates are totipotent.
  • Examples : (1) Physalia (Portuguese man of war)
    (2) Adamsia (sea anemone)
    (3) Pennatula (sea pen)
    (4) Gorgomia (sea fan)
    (5) Meandrina (Brain coral)

PHYLUM : CTENOPHORA (Ktens - Comb, Phors - bearing)

  • They are radially symmetrical, diploblastic and devoid of cnidoblasts, ctenophora are commonly known as sea walnuts / comb jellies.
  • Mostly marine, solitary and pelagic and free swimming animals. They smim by cilia. Tentacles may be present or absent. when present, the number of tentacles is two. They are solid and possess adhesion cells called colloblasts (lasso cells).
  • Digestion is both extracellular and intracellular bioluminescence is well marked in ctenophores
  • They reproduce only sexually. sexes are not separate fertilisation is external. Development is indirect and an immature attained stage is called "cydippid larva". They also have power of regeneration.
  • Examples :-
    (1) Beroe
    (2) Ctenoplana
    (3) Hormiphora
    (4) Pleurobrachia
    (5) Cestum (venus girdle)


They are triploblastic animals exhibit bilateral symmetry along with organ level organization. Free living, commensal or parasitic forms.

  • They are dorso - ventrally flattened. A well defined ventral surface bearing mouth and gonopore is present. Body is unsegmented (except cestoda)
  • Alimentary canal is incomplete (have mouth, no anus) Tapeworms lack the alimentary canal as they absorb nutrients from the host directly through their body surface.
  • Excretory system consists of peculiar flame cells (solenocytes) which are for excretion and osmoregulation. (excretory waste - Ammonia)
  • Adhesive structure like hooks, spines and spines and suckets and adhesive secretions are common in parasitic forms.
  • Nervous system is ladder like. "It consists of the brain / cerebral ganglia Fertilization is always internal Anatomy of the body encourages cross fertilization rather than self fertilization. In some flat worms a sexual reproduction is by transverse binary fission.
  • Development is complicated in flatworms with one or more larval stages (Direct / indirect) usually development is indirect in endoparasites.
  • Eg :
    (1) Taenia (Tapeworm)
    (2) Schistosoma (Blood fluid)
    (3) Fasciola (liver fluke)

Phylum: Nemathelminthes / Aschelminthes

  • They are bilaterally symmetrical, triploblastic and pseudocelomate animals with organ system grade of organization.
  • Mostly acquatic, free lining parasitic. Body cavity is pseudocoel not lined by mesoderm. They have tube within tube type of body plan evolved along protostomic.
  • Alimentary canal is complete with a well developed muscular pharynx. No circulatory and respiratory system.
  • Excretory cell is large giant H shaped cell (or) Renette cell. Nervous system of cerebral ganglia of circumentric nerve ring with anterior and posterior nerves.
  • Sexes are separate (Dioecious). Male usually smaller than female. Development usually direct with no larval stages or indirect with complicated life history. Fertilisation is internal.
    Ascaris (round worm)
    Wuchereria (Filaria worm)
    Ancylostoma (Hoole worm)
  • Sensory organs include rectile organs taste buds statocysts, photoreceptor cells and sometime eyes with lens is also present in some annelids.
  • Reproduction is sexual cleavage spiral and determinate. Larva is trochophore when it is present. Regeneration is also common.
    i) Nereis
    ii) Pheretima (Earthworm)
    iii) Hirudinaria (Blood sucking leech)
  • Hirudinaria secrete anticoagulant hindein from salivary glands. Nereis is dioecious but earthworm and leeches are monoecious.

Phylum: Arthropoda

  • It is the largest phylum in animal kingdom. (∼ 9,00,000 species). Largest class is insects with 7,50,000 species.
  • They are triploblastic, coelomate and bilaterally symmetrical animals. The body is covered by chitinous cuticle which forms exoskeletons.
  • Organ system level organisation is present. They have segmented body, each segment generally bearing a pair of jointed appendages covered by a jointed exoskeleton.
  • Exoskeleton of dead chitinous cuticle is shed in intervals called ecdysis/moulting for growth and development.
  • The body is divided into head, thorax and abdomen. In some cases the head and thorax are fused to form cephalothorax. In some cases thorax and abdomen are fused to form trunk.
  • In insects the thoracic segments have legs and wings, the abdoman has no legs in insects.
  • Digestive system is complete mouth parts are adapted for various modes of feeding.
  • Respiratory organs are gills, book gills or tracheal system. Book gills → Limulus, Book lungs → Spider and scorpion.
  • Excretory organs are green glands / malpighian tubules.
  • Sensory organs like eyes are compound in nature in honey bees, butterflies and moths gustatory receptors are present on their feet. Statocysts / balance organs are present.
  • Circulatory system is open with dorsal often many chambered heart, arteries and blood sinuses of haemocoel.
  • Sexes are separate (dioecious). Reproductive organs and ducts are paired. In land arthropods fertilization is always internal, and in aquatic arthropods fertilization is usually external.
  • Arthropods are oviparous. In some like the scorpions, the eggs hatch within the female body. They bring forth the young ones alive. They are viviparous.
  • Life cycle is generally involves metamorphosis. Larvae and adults may shows a different feeding habit and occupy different habitats.
    (i) Vectors - Mosquito Anopheles, Culex, Aedes, Tse Tse fly; sand fly.
    (ii) Gregarious pest - Locusta (Locust)
    (iii) Economically important - Apis (Honey bee), Bombyx (Silkworm), Laccifer (Lac insect)
    (iv) Living fossil : Limulus (King crab)
    (v) Wingless insect : Lepisma (Silver fish/Book worm)
    (vi) Phylum : Mollusca
  • It is the second largest phylum in Animal kingdom. They are triploblastic, bilaterally symmetrical schizocoelic and unsegmented animals. The segmented mollusca is neopilina.
  • It includes soft bodied invertebrate animals such as snails, slugs, mussels, clams, oysters tusk-shells, squids, octopods and nautili etc.
  • Most mollusca secrete a shell of calcium carbonate that protects and support their soft tissues.
  • The body is organsied into three general region: head, foot and visceral hump. The visceral hump contains digestive tract and other visceral organs.
  • The body is covered by a skin fold called mantle which secrete the shell.
  • Molluscs are typically containing a file like rasping organ called radula which is armed with rows of chitinous teeth. It protrudes out from mouth and catches the food, then wrapped back.
  • Circulatory system is mainly open type / some reduced sinuses are present.
  • Blood often has a "Cu" containing blue respiratory pigment called haemocyanin. Respiration is by gills / pulmonary sac/both. Also may occur through bodies surface.
  • Excretory organ includes kidney which opens into mantle cavity excretion is by paired organ of Bojanus. Another excretory organ called keber's organ (pericardial gland) present in Unio.
  • Sense organs include eyes, statocysts and osphradia (a chemoreceptor to rest chemical nature of water)
  • Sexes are generally separate but some are hermaphrodite. Reproduction is sexual.
  • Fertilization may be external / internal oviparous. The development is either direct or indirect (metamorphosis). In direct take place in trochophore, veliger, glochid.
  • Examples:
    (i) Pila (apple snail)
    (ii) Pinchada (Pearl oyster)
    (iii) Sepia (cuttle fish)
    (iv) Latigo (squid)
    (v) Dentalium (Tusk shell)
    (vi) Chaetopleura (chiton)
    (vii) Octopus (devil fish)
    (viii) Aplysia (sea hare)

Phylum : Echinodermata (spine body)

  • Mostly marine animals. There are no parasitic forms. Generally live at sea bottom, some are pelagic and few are sessile.
  • Three characters make the echinoderms closer to chordates:
    (i) They have tube within tube type of body plan which has evolved along deuterostomic evolutionary line.
    (ii) They posses a true cedom called enterocoelom.
    (iii) They have mesodermal endoskeleton made of calcareous planes / ossicles.
  • Symmetry is bilateral during larval stage and pentamerous radial in adults.
  • Ambulacral system (water vascular system) is characteristic feature of phylum echinodermata. A performed plane, madreporite is present in this system. The pones of madreporite allow water into the system.
  • Tubefeet of this system help in locomotion. coelom is enterocoelom. Body bears spines and pincer like pedicellariae. Spines are for production of body pedicellariae keep the body surface clear of debris and minute organisms.
  • Digestive tract is complete. Vascular system is open and includes haemal and perihaemal system. The blood is often without a respiratory pigment. There is no heart.
  • Respirator organs include dermal branchiae, tube feet, respiratory tree and bursae. No excretory organ (excretory product : Ammonia)
  • Nervous system doesn't contain brain. They have radial and circumoral ring nerves. Poorly developed sense organ is present.
  • Usually diecious, fertilisation is usually external. Development is indirect through free swimming larval forms. Phenomenon of autotomy and regeneration is present.
  • Bipinnaria and brachiolaria larvae are present in the development of star fish.
    (i) Asterias (star fish)
    (ii) Echinus (sea urchin)
    (iii) Antedon (sea lily)
    (iv) Cucumaria (sea cucumber)
    (v) Ophiura (Brittle star)

Phylum Hemichordata (Stomochordata)

  • Earlier they are considered as a sub-phylum under chordata. But it is separate phytum under non chordata.
  • This animals have gills slits bulb they are dorsal in position. Noso cord is absent.
  • Small group of animals mostly present in marine with organ / organ system level of organization. They are coelomate, bilaterally symmetrical and triploblastic.
  • Body is cylindrical and composed of an anterior proboscis, a collar and a long trunk.
  • Circulatory system is open type excretory organ is proboscis gland. Respiration takes place through gills.
  • Sexes are separate and fertilization is external. Development is mostly indirect through a free swimming tornaria larva.
    Balanoglossus (acorn / tongue worm)

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