Diversity in Living Organisms

Phylum 1. Porifera

• Porifera means organisms with holes.
• They are simplest multicellular and diploblastic animals.
• These are non-motile animals that are attached to some solid support. They are commonly called sponges.
• The cells are loosely held together in a gelatinous matrix.
• These are asymmetrical or radially symmetrical.
• Body is perforated with numerous pores. Pores on the bodies create a canal system which helps in circulation of substances.
• Their body is not differentiated into head and tail. They don’t have well-developed organ or organ system.
• Mouth, digestive cavity and anus are absent.
• Examples: Leucosolenia, Sycon

Phylum 2. Coelenterata(Cnidaria)

• The term is derived from the Greek word “koilos” which means hollow-bellied.
• These are Aquatic (living in water), mostly marine. Some live in colonies like corals and others solitary like Sea anemone.
• Coelenterates are multicellular, diploblastic animals.
• Their Body shows radial symmetry.e., these animals have similar parts arranged around a common central axis. Sections of such animals at any radius have similar structure to that of others.
• A central gastrovascular cavity coelenteron is present which lacks anus but has a mouth which is surrounded with short and slender tentacles.
• Respiratory, circulatory and excretory organs are absent.
• Nervous system is primitive, has only network of nerve cells.
• Examples: Hydra, Obelia, Millepora (coral), Physalia

Phylum 3. Platyhelminthes

• Platyhelminthes are commonly known as flatworms.
• They are bilaterally symmetrical (dorsoventrally flattened animals.) i.e. body of these animals is divisible into two equal halves longitudinally. The two halves (right or left) are mirror image of each other.
• These animals have thin, soft, leaf-like or ribbon-like body.
• They are triploblastic animals whose tissues are differentiated from three layers of cell.
• Digestive cavity (when present) with a single opening, the mouth
• Suckers and hooks are generally present.
• Circulatory and respiratory systems and skeleton are not present.
• They are Hermaphrodites, ie, both male and female reproductive organs occur in the same individual.
• They are either free-living (Planaria) or parasitic (Liver flukes).
• Examples: Dugesia, Planaria, tapeworm.

Phylum 4. Nematoda

• Phylum Nematoda consists of nematodes or roundworms.
• These are bilaterally symmetrical, triploblastic, pseudocoelomate and unsegmented animals.
• Their Body is round, slender and tapering at the two ends, cylindrical or flattened.
• Body of these animals is covered with a tough and resistant cuticle.
• Alimentary canal is straight and complete with mouth and anus; pharynx is muscular.
• Sexes are separate in these animals.
• Most forms are parasitic and cause diseases such as elephantiasis, ascariasis, etc. however; some are free-living soil or water.
• Examples: Ascaris (round-worm), Ancylostoma (hook-worm)

Phylum 5. Annelida

• Annelids are commonly known as segmented or ringed worms.
• Their Body is triploblastic, bilaterally symmetrical, soft, elongated, vermiform and cylindrical or dorsoventrally flattened.
• Body is metamerically segmented externally
• Exoskeleton is absent and body is covered by a thin cuticle.
• Locomotory organs are segmentally arranged paired lateral appendage, chitinous setae.
• Alimentary canal is tube-like, complete and extends straight from mouth to anus.
• Habitat: marine, freshwater, and land.
• Ex: Earthworm, Leech.

Phylum 6. Arthropoda

• Arthropod means jointed legs. In other words, animals which have jointed appendages belong to this phylum. This is the largest phylum in the animal kingdom.
• These are Triploblastic, bilaterally symmetrical and metamerically segmented animals
• Their Body has three regions – head, thorax and abdomen.
• Exoskeleton or cuticle is present in these animals.
• Each body segment (somite) usually bears paired lateral and joined legs or appendages.
• Body cavity is filled with blood. This is called Haemocoel
• Alimentary canal is complete, mouth and anus lie at opposite ends of the body.
• Respiration is carried out through general body surface, by gills, air tubes (tracheae) or book-lungs.
• Circulatory system is open with dorsal heart but they have well-defined blood vessels.
• Sexes are usually separate.
• Arthropoda forms the largest phylum of Animal kingdom. About 900,000 species are known.
• Examples: Limulus (king-crab), palamnaeus (scorpion); Aranea (spider), Sarcoptes (itch-mites), Argus (tick)

Phylum 7. Mollusca

• Their Body is soft, bilaterally symmetrical, with little segmentation and without appendages.
• Body of these animals is divisible into an anterior head, a ventral muscular foot, a hard dorsal visceral mass.
• Digestive tract has a simple structure.
• Respiration is carried out through gills (called ctenidia), mantle or a “lung” of the mantle.
• Circulatory system is open.
• Excretion is carried out by a pair of kidneys
• Sexes are usually separate.
• Sensory organs of touch, smell, taste, equilibrium, and vision are present.
• Examples: pila (apple snail), Helix (garden snail), Dentalium, (tusk shell), Unio (fresh water mussel)

Phylum 8. Echinodermata

• The term is derived from the Greek words, echinos meaning hedgehog and derma meaning skin. Thus, echinoderms are spiny-skinned animals.
• They are Simple animals which may be star-like, spherical or elongated.
• Their Body is triploblastic, coelomate, unsegmented (nonmetrameric) and radially symmetrical.
• Body of these animals lacks head, but has oral and aboral surfaces.
• Body wall of these animals is covered with spiny hard calcareous (calcium carbonate) plates
• Digestive system is usually complete.
• Excretory organs absent.
• Free-living marine animals.
• Example: Antedon (father star), Cucumaria (sea cucumber), Echinus (sea urchin), Asterias (star fish or sea star)

Phylum 9. Hemichordata

• Their Body is soft bilaterally symmetrical.
• Body is divided into proboscis, collar (collarette) and trunk.
• These animals resemble chordates only in having pharyngeal gill slits. They lack notochord and true dorsal nerve cord.
• “Notochord” is present in proboscis.

Differences between non-chordates and chordates.