జంతుశాస్త్రం

జంతుశాస్త్రం

 Points to Remember during Preparation
 *    The changes which considered as the first, second and the third key transitions in the animal organi- zation are evolution of tissues, development of bilateral symm- etry and origin of the body cavity respectively.
 Porifera
 *    The first metazoan phylum is Porifera which belongs to sub- kingdom Parazoa. It remains an evolutionary blind offshoot.
 *    It shows cellular level of orga-nization.
 *    Poriferans are generally known as sponges as they have porous body.
 *    Sponges have  water transport system or canal system which helps in gathering food (filter feeders), respiratory exchange of gases and removal of wastes.
 *    Nutrition in sponges is holozoic and digestion is intracellular in choanocytes.
 *    Body of sponges is supported by skeleton made up of calcareous or siliceous spicules or spongin fibres or both.
 *    Classification of Porifera is based on the nature of skeleton and divided into three classes like Calcarea, Hexactinellida and Demospongiae.
 *    Larval stages are parenchymula, trichimella and amphiblastula.
 Cnidaria
 *    It belongs to grade Radiata and diploblastica.
 *    They consist cnidocytes or cnidoblasts or stinging cells.
 *    Radial symmetrical animals.Sea anemones are biradially sym-metrical.
 *    First metazoans with tissue level of organization.
 *    They have coelenteron or gastro-vascular cavity for both digestive and circulatory functions.
 *    Digestion is both extracellular in coelenteron and intracellular in nutritive muscular cells of endoderm.
 *    Two basic body forms are polyp and medusa.
 *    Some show metagenesis or alternation of generations with polypoid forms which produce medusa asexually and medusa which produce polypoid forms sexually. E.g.,Obelia.
 *    Planula is the free swimming ciliated larva.
 *    Based on the nature of zooids or basic body forms, this phylum has three classes like Hydrozoa, Scyphozoa and Anthozoa. Students should prepare the characters of Anthozoa.
 Ctenophora
 *    These are sea walnuts or comb jellies or sea gooseberries.
 *    Cnidocytes are absent in them.
 *    Eight external rows of ciliated comb plates are present.
 *    Glue cells in the form of  lasso cells or colloblasts are present for capturing of food.
 *    They show bioluminescence.
 *    Larva is cydippid.
 *    It includes two classes namely Tentaculata and Nuda.
 Platyhelminthes
 *    It is the first bilaterally symme-trical triploblastic phylum.
 *    It is the first group of animals with organ-system level of organization.
 *    It is acoelomate phylum with solid bauplan.
 *    Flame cells or proto nephridia help in osmoregulation and excre-tion.
 *    Development includes stages like miracidium, sporocyst, redia, cercaria etc.,
 *    Some show polyembryony and others show regeneration capa-city.
 *    It includes three classes like Tur bellaria, Trematoda and Cestoda.
 *    Cestodans show  pseudometa-merism.
 Nematoda
 *    It is pseudocoelomate phylum.
 *    The first tube-within-a-tube body organization appears in this phylum.
 *    Collagenous cuticle is unique feature as the collagen is the fundamental feature of plants.
 *    Sense organs are amphids and phasmids.
 *    Four moultings occur during life history.
 *    They show eutely with constant number of body cells except the cells in gonads as the cell division ceases after the completion of development of embryo.
 *    Growth occurs due to the increasing of size of cells rather than the number of cells.
 *    It includes two classes like Aphasmidia and Phasmidia.
 Annelida
 *    It is the first phylum with metamerically segmented body and true coelom (schizocoelom)
 *    Coelomic fluid acts as hydrostatic skeleton.
 *    Direct dissolved state of respiratory pigments like haemo- globin and chlorocruorin in plasma is the unique feature of invertebrates.
 *    Nerve ring is formed around pharynx and nerve cord is ganglionated double ventral type.
 *    Ectodermal originated nephridia help in osmoregulation and excretion.
 *    Trochophore larva appears in life history.
 *    It includes three classes like Polychaeta, Oligochaeta and Hirudinea.
 *    Polychaetes are bristle worms. They have parapodia with many setae. Polychaetes are without clitellum and gonoducts. Develop ment includes trochophore larva. Polychaetes are unisexual.
 *    Oligochaetes include earthworms with clitellum. Oligochaetes are bisexual.
 *    Ectoparasitic leeches belong to the class Hirudinea. They have definite number of segments without internal segmentation.
 *    Leeches have botryoidal tissue in coelomic cavity.
 *    Leeches are bisexual. Leeches have copulatory organ, cirrus in male reproductive system. It causes internal fertilization.
 Note:
 i)    Students should prepare comparative table to study  various characters of  Hirudinea and remaining classes Polychaeta and Oligochaeta. It helps them both in  IPE and EAMCET.
 ii)    Type study of earthworm, Pheretima is also given in this topic. Students should practice diagrams of alimentary canal, nephridial system  and reproductive system thoroughly.
 
 IPE Weightage:
 l        6 marks weightage is present for this unit in IPE.
 Important questions for IPE:
 1.        Characters of Anthozoans?
 2.        Characters of Polychaetes?
 3.        Comparison of hiurdineans with polychaetes and oligochaetes?
 4.        Comparison of centipede and millipede?
 5.        Characters of crustaceans?
 6.        Advanced features of cephalopods?
 7.        Characters of echinoids?
 
 EAMCET Weightage:
 *          2-3 questions are possible to ask from this unit in EAMCET.
 *        Students should concentrate over comparative study of various systems of all the phyla.
 *        They should practice the names of animals given as examples under all the phyla.
 *        Preparation from basic level, regular practice, revision of contents frequently and practicing of question banks to analyze their preparation level are some of the techniques to improve the marks in this unit.