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Notes - Phylum-Platyhelminthes

  Phylum-Platyhelminthes     Phylum Platyhelminthes.   (i) Introduction : Bilateral and protostominal ?organ grade? eumetazoans without a body cavity (acoelomates). ?Platyhelminthes? means flatworms (Gr., platys = flat; helmins = worms); their body is dorsoventrally flattened. About 10,000 species known.   (ii) Brief History : Aristotle mentioned tapeworms, but scientific studies of flatworms began only in the 18th century. It was Gegenbaur (1859) who placed these in a separate group and suggested the present name of the phylum.           (iii) Salient feature             (1) They are dorso ventrally flattened like a leaf             (2) They show organ grade of organization             (3) They are acoelomate animals. The cavity in platyhelminthes is filled with mesenchyme or parenchyma (4) They are triploblastic animals. The cells of the body wall are arranged in three layers.They are the ectoderm, the mesoderm and the endoderm (5) They are bilaterally symmetrical animals. The body of the animal can be divided into two equal similar halves through only one plane. Animals with this symmetry have definite polarity of anterior and posterior ends. (6) Some members have segmented body. The segmentation in platyhelminthes is called pseudometamerism (7) Many of the parenchyma cells give rise to muscle fibres.The muscle fibres are arranged in circular, longitudinal and vertical layers. (8) The digestive system is completely absent from Cestoda and Acoela. The alimentary canal is branched more...
Catgeory: NEET

Notes - Phylum-Nemathelminthes

  Phylum-Nemathelminthes    Phylum Nematoda (= Nemathelminthes).   (i) Introduction : Bilateral and protostomial ?organ grade? eumetazoans in which the space between body wall and alimentary canal is a false body cavity, or pseudocoel, derived from embryonic blastocoel. The term ?Nematoda? literally means ?threadworms? or ?roundworms? (Gr., nema = thread + eidos = form). About 12,000 species known. (ii) Brief History : Ancient people were familiar with certain large-sized nematode parasites of domestic animals. Minute nematodes were discovered only after the invention of microscope. Linnaeus (1758) included these in ?Vermes? Rudophi (1793, 1819) included these under ?Nematoidea? Gegenbaur (1859) ultimately proposed ?Nemathelminthes? for these.             (iii) Salient features (1) Many endoparasites of various animals and plants; others free?living and widely distributed in all sorts of water and damp soil.             (2) Mostly minute or small; some large (1 mm to 25 cm); some upto several metres long.             (3) Slender, cylindrical, elongated body usually tapering towards both ends, and unsegmented. (4) Body wall formed of a thick, tough and shiny cuticle, a syncytial hypodermis beneath cuticle, and innermost layer of peculiar, large and longitudinally extended muscle cells arranged in four quadrants.             (5) The false body cavity, or pseudocoel is spacious, with a fluid but no free cells             (6) Straight alimentary tract with terminal mouth and anus (7) Circulatory system and respiratory organs absent. A simple excretory system, comparatively simpler or complicated sensory organs, and a well?developed nervous system present more...
Catgeory: NEET

Notes - Phylum-Annelida

  Phylum-Annelida   Phylum Annelida.   (i) Introduction : Bilateral and protostomial eucoelomate eumetazoans whose long, narrow and worm like body is divided into ring-like, true or metameric segments (Gr., annelus = little ring), and the skin usually bears unjointed, chitinous appendages, termed setae. Commonly known as ?segmented worms?. About 9,000 species known.   (ii) Brief History : Linnaeus (1758) included all soft?bodied worms in ?Vermes?. Lamarck (1801) established phylum annelida for higher types of worms.                   (iii) Salient features            (1) Annelids are bilaterally symmetrical animals          (2) They have organ-system grade of organization          (3) They are coelomate animals          (4) They have triploblastic body wall          (5) The muscle layers are thick in the body wall. Hence the body wall is said to be dermomuscular (6) The body is divided into a numerous segments called the metameres. The segmentation is known as metamerism          (7) The body is covered with a thin cuticle.          (8) Locomotory organs are setae.          (9) Digestive system is well developed          (10) Blood vascular system is a closed type          (11) Excretory system is formed of segmentally arranged nephridia. more...
Catgeory: NEET

Notes - Phylum- Arthropoda

Phylum-Arthopoda   Phylum Arthropoda.   (i) Introduction : Bilateral and protostomial eucoelomate eumetazoa with metamerically segmented body and each segment bearing a pair of jointed locomotory appendages. ?Arthopoda? literally means animals bearing jointed feet (Gr., arthron = jointed + podos = foot). These are extremely successful animals due to a protective exoskeleton and jointed appendages. That is why, more than  lac arthropod species are known as against about  lac species of the remaining animals.  
 
 
                                     (ii) Brief History : Aristotle described a few crabs and other arthropods. Linnaeus included all such animals in his group ?Insecta?. Lamarck divided this group into there classes ? Crustacea, Hexapoda and Archnida. Finally, Vonsaibold (1845) established the phylum Arthropoda for these animals.   (iii) Salient features (1) Occur widely on land, in air, and in all sorts of water, form snowy tops of high mountains to the depths of ocean. Many are parasites of other animals and plants. Hence, the phylum is of great economic importance. (2) Bilateral, triploblastic body segmented and also divided into head, thorax more...
Catgeory: NEET

Notes - Phylum Mollusca

  Phylum-Mollusca     Phylum Mollusca.   (i) Introduction : Basically bilateral and protostomial eucoelomate eumetazoans whose soft body (L., mollis or molluscum = soft) is unsegmented and enclosed within a skin?fold (mantle) which usually secretes a calcareous shell. About 80,000 existing and 35,000 extinct species known. Aquatic or terrestrial. Snails and mussels found along banks of freshwater bodies and the oysters, shanks (shose conch?shell is commonly blown in religious ceremonies) and cowries of the sea are common molluscs. Malacology or Conchology is the branch of study of molluscs and their shells. Molluscs are of some economic importance; man uses some as food; shells of some are used for making buttons, beads, etc.   (ii) Brief History: Aristotle described a number of molluscs. Johnston (1650) proposed the name of the phylum.           (iii) Salient Features             (1) Molluscs are multicellular organisms             (2) They have a bilateral symmetry, but snails are asymmetrical             (3) They are triploblastic animals.             (4) They are coelomate animals. True coelom is reduced the haemocoel is well developed in them.             (5) They have organ system grade of organization.             (6) The body is soft and unsegmented.             (7) The soft body is covered by a fleshy fold of the body wall. It is called mantle.             (8) The molluscs are provided with one or two calcareous shells. The shells may be external or internal.             (9) Respiration more...
Catgeory: NEET

Notes - Phylum Echinodermata

  Phylum-Echinodermata    Phylum Echinodermata.   (i) Introduction : Bilateral and deuterostomial eucoelomate eumetazoa with rough, tough and leathery skin due to dermal skeleton of usually spiny, calcareous ossicles; and the basic bilateral symmetry of larva modified, in the adult, to a pentamerous radial symmetry. The term ?Echinodermata? means spiny skin (Gr., echinos = spiny + dermatos = skin). About 6,000 living and 20,00 extinct species known.   (ii) Brief History : Although Jacob Klein (1738) had earlier coined the name ?Echinodermata?, yet Linnaeus included these animals under ?Mollusca?, and Lamarck under his class ?Radiata? as ?Echinodermes?. Finally, Leuckart (1847) raised the group to the status of a separate phylum.               (iii) Salient features             (1) Echinoderms are exclusively marine beings.             (2) They are triplobalstic and coelomate animals. (3) They have radially symmetrical body. The radial symmetry is due to sedentary or sessile mode of life and it is a secondary character in echinoderms.             (4) They have organ system grade of organization.             (5) They have well developed endoskeleton formed of calcareous ossicles and spines. (6) They have a water?vascular system with tube?feet for locomotion, feeding and respiration.             (7) Circulatory system is of the open?type.             (8) The sensory organs are poorly developed.             (9) The excretory organs are absent.             (10) They have pedicellariae. more...
Catgeory: NEET

Notes - Phylum Chordata

  Chordata    Chordata.               (i) General Characters of Phylum Chordata             (1) Aquatic, aerial or terrestrial. All free-living with no fully parasitic forms.             (2) Body small to large, bilaterally symmetrical and metamerically segmented. (3) A post anal tail usually projects beyond the anus at some stage and may or may not persist in the adult.             (4) Exoskeleton often present; well developed in most vertebrates.             (5) Body wall triploblastic with 3 germinal layers: ectoderm, mesoderm and endoderm.             (6) Coelomate animals having a true coelom, enterocoelic or schizocoelic in origin.             (7) A skeletal rod, the notochord, present at some stage in life cycle. (8) A cartilaginous or bony, living and jointed endoskeleton present in the majority of members (vertebrates).             (9) Pharyngeal gill slits present at some stage; may or may not be functional.             (10) Digestive system complete with digestive glands. (11) Blood vascular system closed. Heart ventral with dorsal and ventral blood vessels. Hepatic portal system well developed.             (12) Excretory system comprising proto-or meso- or meta-nephric kidneys.             (13) Nerve cord dorsal and tubular. Anterior end usually enlarged to form brain.             (14) Sexes separate with rare exceptions.   Outline Classification of Phylum Chordata more...
Catgeory: NEET

Notes - Class-Pisces

  Superclass Pisces                                                                     Superclass Pisces.                                         Class 1. Chondrichthyes (Cartilaginous Fishes)          (i) General characters.             (1) Mostly marine and predaceous.             (2) Body fusiform or spindle shaped. (3) Fins both median and paired, all supported by fin rays. Pelvic fins bear claspers in male. Tail heterocercal.             (4) Skin tough containing minute placoid scales and mucous glands. (5) Endoskeleton entirely cartilaginous, without true bones (Gr. chondros, cartilage + ichthys, fish). Notochord persistent. Vertebrae complete and separate. Pectoral and pelvic girdles present. (6) Mouth ventral. Jaws present. Teeth are modified placoid scales. Stomach J-shaped. Intestine with spiral valve. (7) Respiration by 5 to 7 pairs of gills. Gill-slits separate and uncovered. Operculum absent. No air bladder and lungs. (8) Heart 2?chambered (1 auricle and 1 ventricle). Sinus venosus and conus arteriosus present. Both renal and portal systems present. Temperature variable (poikilothermous). more...
Catgeory: NEET

Notes - Class Amphibia

  Class-Amphibia      Class Amphibia.             (i) General characters (1) Aquatic or semi aquatic (freshwater), air and water breathing, carnivorous, cold?blooded, oviparous, tetrapod vertebrates.             (2) Head distinct, trunk elongated. Neck and tail may be present or absent. (3) Limbs usually 2 pairs (tetrapod), some limb less Toes 4-5 (pentadactyle) or less. Paired fins absent. Median fins, if present, without fin rays.             (4) Skin soft, moist and glandular. Pigment cells (chromatophores) present.             (5) Exoskeleton absent. Digits claw less. Some with concealed dermal scales.             (6) Endoskeleton mostly bony. Notochord does not persist. Skull with 2 occipital condyles. (7) Mouth large. Upper or both jaws with small homodont teeth. Tongue often protrusible. Alimentary canal terminates into cloaca. 8) Respiration by lungs, skin and mouth lining. Larvae with external gills which may persist in some aquatic adults. (9) Heart 3?chambered (2 auricles + 1 ventricle). Sinus venosus present. Aortic arches 1-3 pairs. Renal and hepatic portal systems well developed Erythrocytes large, oval and nucleated. Body temperature variable (poikilothermous).             (10) Kidneys mesonephric. Urinary bladder large. Urinary ducts open into cloaca. Excretion ureotelic.             (11) Brain poorly developed. Cranial nerves 10 pairs. (12) Nostrils connected to buccal cavity. Middle ear with a single rod-like ossicle, columella. Larval forms and some aquatic adults with lateral line system. (13) Sexes separate. Male without copulatory organ Gonoducts open into cloaca. Fertilization mostly external. Females mostly oviparous. (14) Development indirect. Cleavage holoblastic but unequal. No extra?embryonic membranes. Larva more...
Catgeory: NEET

Notes - Class-Reptilia

  Class-Reptilia   Class Reptilia.   (i) General Characters: Reptiles represent the first class of vertebrates fully adapted for life in dry places on land. They have no obvious diagnostic characteristics of their own that immediately separate them for other classes of vertebrates. The characters of reptiles are in fact a combination of characters that are found in fish and amphibians on one hand and in birds and mammals on the other. The class name refers to the mode of locomotion (L., repere or reptum, to creep or crawl), and the study of reptiles is called Herpetology (Gr., herpeton, reptiles). (1) Predominantly terrestrial, creeping or burrowing, mostly carnivorous, air?breathing, cold?blooded, oviparous and tetrapodal vertebrates.             (2) Body bilaterally symmetrical and divisible into 4 regions-head, neck, trunk and tail. (3) Limbs 2 pairs, pentadactyle. Digits provided with horny claws. However, limbs absent in a few lizards and all snakes.             (4) Exoskeleton of horny epidermal scales, shields, plates and scutes.             (5) Skin dry, cornified and devoid of glands.             (6) Mouth terminal. Jaws bear simple conical teeth. In turtles teeth replaced by horny breaks.             (7) Alimentary canal terminates into a cloacal aperture. (8) Endoskeleton bony. Skull with one occipital condyle (monocondylar). A characteristic T?shaped inter clavicle present. (9) Heart usually 3?chambered, 4?chambered in crocodiles. Sinus venosus reduced. 2 systemic arches present. Red blood corpuscles oval and nucleated. Cold?blooded.             (10) Respiration by lungs throughout life.             (11) Kidney metanephric. Excretion uricotelic.             (12) Brain with better development of cerebrum than in Amphibia. Cranial nerves 12 pairs. more...
Catgeory: NEET

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