Animal Kingdom-General Characters-Bsc Complementary Zoology Notes

• Features
• Include entire fauna of living world
• Chlorophyl:absent
• Mostly motile
• Nutrition:holozoic or parasitic some are detritivore(earth worm)
• Respiration:aerbic or anaerobic in parasitic
Levels of Organisation
1. Cellular Level: In unicellular animals and some multicellular animals like sponges , the cell is responsible for all the
metabolic activities in the animal body. This type of organization of function is termed as cellular level of
organization.
2. Tissue Level: In certain animals like Coelenterates. cells performing the same function are arranged in a group.
3. Organ Level: Some animals like flatworms form specialized organs for specific functions.
4. Organ System Level: In higher and complex animals various organs group to form a complex organ system to
perform specific function.
Symmetry
• Assymetric animals like Sponges cannot be divided in to two equal halves.
• Radial Symmetric animals: When any plane passing through the central axis of the body divides the
organism into two identical halves, it is called radial symmetry. Coelenterates, ctenophores and
echinoderms have this kind of body plan.
• Bilateral Symmetry: Animals like annelids, arthropods, etc., where the body can be divided into
identical left and right halves in only one plane, exhibit bilateral symmetry.
Diploblastic and triploblastic animals
• Animals in which the cells are arranged in two egerm layers, an external ectoderm and an internal
endoderm, are called diploblastic animals, e.g., coelenterates. An undifferentiated layer, mesoglea, is
present in between the ectoderm and the endoderm.
• Triploblastic animals:Animals in which the developing embryo has a third germinal layer, mesoderm, in
between the ectoderm and endoderm, are called triploblastic animals .Eg all animals from platyhelminthes
to chordates.
• In cnidaria between ectoderm and endoderm there is jelly like mesogloea.In sponges mesenchyme is
present between ectoderm and endoderm.
Metamerism
In some animals, the body is externally and internally divided into segments with a serial repetition of at least some
organs. For example, in annelids, the body shows this pattern called metameric segmentation and the phenomenon
is known as metamerism.
Notochord
Notochord is a mesodermally derived rod-like structure formed on the dorsal side during embryonic development
in some animals. Animals with notochord are called chordates and those animals which do not form this structure
are called non-chordates, e.g., porifera to echinoderms.
Coelom
The body cavity present in between gut and body wall, which is lined by mesoderm is called coelom.
Acoelomates: The animals in which the body cavity is absent are called acoelomates, e.g., platyhelminthes.
Pseudoceolomates: In some animals, the body cavity is not lined by mesoderm, instead, the mesoderm is
present as scattered pouches in between the ectoderm and endoderm. Such a body cavity is called
pseudocoelom and the animals possessing them are called pseudocoelomates, e.g., aschelminthes.
Coelomates:Animals possessing coelom are called coelomates, e.g., annelids, molluscs, arthropods,
echinoderms, hemichordates and chordates.
Schizocoelom:It develops as a split in the mesoderm sheet.eg.Annelids,arthropods and mollusca.
Enterocoelom:Coelom arises from the wall of gut or enteron as hollow outgrowth.eg.Echinodermata and
chordata.
In arthropoda and mollusca coelom is reduced .the space in between viscera grow in size and produce large
cavity.The cavity contains blood and is known as haemocoel.
Pseudometamerism:False segmentation.Found in tapeworms