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DISCOVER

ANIMAL KINGDOM

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Published in: Science
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WILL PROVIDE BRIEF INSIGHT ABOUT ANIMALS

Pathikrit B / Bharuch

10 years of teaching experience

Qualification: Ph.D in Chemistry

Teaches: Biology, Chemistry, Mathematics, Zoology, Microbiology, AIPMT, Botany

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  1. ANIMAL KINGDOM Levels of organization: Cellular level, Tissue level, Organ level and Organ system level Circulatory System: Open type: Blood pumped out through heart. Cells and tissues are directly bathed in it. Closed type: Blood is circulated through vessels. Symmetry: Asymmetrical: Cannot be divided into equal halves through median plane. e.g., Sponges. Radial symmetry: Any plane passing through central axis can divide organism into equal halves. e.g., Hydra. Bilateral symmetry: Only one plane can divide the organism into equal halves. e.g., Annelids and Arthropods. CLASSIFICATION ON BASIS OF GERMINAL LAYERS: Diploblastic: Cells arranged in two embryonic layers i.e. external ectoderm and internal endoderm. (Mesoglea may be present in between ectoderm and endoderm) e.g., Coelenterates. (Cnidarians) Triploblastic: Three layers present in developing embryo i.e., ectoderm, endoderm and mesoderm. e.g., Chordates. Coelom (Body cavity which is lined by mesoderm) Coelomates: Have coelom e.g., Annelids, Chordates etc. Pseudo coelomates: No true coelom as mesoderm is present in scattered pouches between ectoderm and endoderm. e.g., Aschelminthes. Acoelomates: Body cavity is absent. E.g. Platyhelminthes.
  2. Metamerism: If body is externally and internally divided into segments with serial repetition of at least some organs then phenomenon is called Metamerism. e.g., Earthworm. Notochord: Rod-like structure of mesodermal origin, formed during embryonic development on the dorsal side. e.g., Chordates. INVERTEBRATE PHYLA PHYLUM PORIFERA: Also called sponges, usually marine and asymmetrical with cellular level of organization. Diploblastic (outer pinacoderm, inner chaonoderm with mesoglea in between), acoelomate with cell aggregate body plan. Different cell types are present in the body wall of sponges--- pinococytes, porocytes, amoebocytes thesocytes, choanocytes (ingestion of food) etc. Food gathering, respiratory exchange and removal of wastes occur through water canal system. Digestion intracellular occurring partly in choanocytes and partly in trophocytes. Ostia (minute pores all over the body), spongocoel (body cavity) and osculum (large pore, single or numerous) help in water transport. They are lined by choanocytes (collar cells). Body wall has calcareous spicules and proteinaceous spongin fibers. Spicules are branched and can be monaxonic, triaxonic, tetraxonic and polyaxonic. Asexual Reproduction occurs by fragmentation, external budding, gemmules and reduction bodies (Under extreme unfavorable conditions). Sexual reproduction --- Animals are hermaphrodite. Fertilization internal. Development is indirect, with larval stage which metamorphoses to adult. Two common larval types are amphiblastula and parenchymula. E.g. Sycon sp, Euspongia sp PHYLUM COELENTERATA:
  3. Also called Cnidarians. Are usually marine and exhibits polymorphism--- existence of same individual in two morphologically distinct forms cup-shaped polyp and umbrella- shaped medusa. Exception Obelia with three distinct forms --- polyp, medusa and blastostyles. Radially symmetrical, tissue level of organization, and diploblastic—presence of two germ layers, ectoderm and endoderm Sessile or free-swimming. Appendages absent except tentacles. Have tissue level of organization Diploblastic. Presence of cnidoblast, for anchorage, defense and capture of prey. Central body cavity called gastro-vascular cavity or coelenterone. Digestion extracellular and intracellular. Blind sac type body plan, with one opening called hypostome. Body wall composed of calcium carbonate. Exhibit two body forms: polyp and medusa e.g., Hydra, Aurelia. Alternation of generation between body forms called Metagenesis occurs in Obelia where Medusa sexually reproduced and polyp asexually reproduced. •e.g., Physalia, Adamsia. PHYLUM CTENOPHORA: Also called as sea walnuts or comb jellies, are exclusively marine, radially symmetrical. Have tissue level organization, are diploblastic. Most ctenophores emit light and have special light producing cells called photocytes. Digestion both extra and intracellular. Body has eight external rows of ciliated comb plates for locomotion. Independent muscle network also present. Special adhesive cells called lasso cells or colloblasts are present over the tentacles.
  4. Presence of aboral sense organ called statocyst for maintaining balance Sexes are not separate i.e. hermaphrodite. Reproduce only by sexual methods. External fertilization. Indirect development e.g., Ctenoplana PHYLUM PLATYHELMINTHES Body dorsiventrally flattened, ribbon-like, with organ level of organization. Triploblastic animals with single aperture for both mouth and anus, pseudo segmentation present due to repeated budding. Syncytial epidermis with three types of muscles--- outer circular, middle oblique and inner longitudinal. Digestive tract incomplete with both the types of digestion, Gaseous exchange through body surface. Flame cells act as excretory organs, ammonia and fatty acids are common excretory products. Free living forms have different types of receptors for perceiving sensations, parasitic forms are devoid of any receptor. Nervous system is polarized--- cerebral ganglia, nerve cords and commissures. Reproductive system well developed, moneocious, development mostly indirect with free living larval stages. E. g. Taenia solium PHYLUM ARTHROPODA: Largest animal phylum consisting of 82% of all animal and 63% of all organisms. Are found in almost all types of habitat and are cosmopolitan in distribution
  5. Bilaterally symmetrical, triploblastic, externally segmented with organ system level of organization showing tube within —tube plan True coelom with haemocoel present. True coelom reduced and found around reproductive and excretory organs. Cephalization distinct with head and compound eyes present, eyes with similar units called ommatidia. Jointed appendages present in paired form. The paired jointed appendages are modified to form antennae, mouth parts etc. Chitinous segmented exoskeleton present which undergoes periodic shedding called moulting or ecdysis. Digestive system complete with all types of nutrition. Gaseous exchange occurs through body surface. Other organs of respiration include book gills, gills, trachea, siphon etc. Excretory system composed of green glands or malphigian tubules. Excretory products are ammonia or urea. Open type of circulatory system with heart present. Blood colourless and called haemolymph. Endocrine system occurs in most species. An endocrine hormone called pheromone is secreted which controls moulting and other reproductive behavior. Asexual reproduction absent though sexual reproduction is pronounced in all the species. Sexual dimorphism is present with external or internal fertilization. Development direct or indirect with one to many larval stages. E. g. Apis indica PHYLUM ASCHELMINTHES Body Form ---- Cylindrical, elongated body with bilateral symmetry with organ triploblastic condition and organ system level of organization. Pseudocoelom condition present. Body Wall--- The body wall consists of an elastic cuticle, an epidermis and a muscular layer. Longitudinal muscles present.
  6. Segmentation and Cephalisation --- Absent, internal cephalisation is present but externally there is little differentiation between the anterior and posterior regions. Digestive system ---Well developed with mouth, muscular pharynx, intestine and anus present. The digestive tract is devoid of muscles. Respiratory system --- Absent. Mode of respiration aerobic in free living forms and anaerobic in parasites. Blood vascular system absent. Transportation takes place with the help of pseudocoelomic fluid. Excretion occurs with the help of protonephridia. Excretory products include ammonia and urea. Sensory system consists of different types of receptors namely ciliated spots, eye spots etc. Reproduction — Asexual reproduction absent, fertilization internal, animals are oviparous and ovoviviparous. Cleavage is spiral with direct development. Eutely --- In this the number and nuclei of cells do not change after maturity. It is a characteristic feature of roundworms that has been discovered recently. PHYLUM ANNELIDA Body form --- Elongated, cylindrical or flattened with bilateral symmetry, organ system level of organization and triploblastic condition. Segmentation and Cephalisation — Body has metameric segmentation. A definite head with feeding, sensory and nervous centres are present. Digestive system --- complete with extracellular digestion. Respiratory system — Cutaneous respiration occurs through skin surface in most of the members, other show branchial respiration. Circulatory system --- closed circulatory system present in annelids. Blood reddish in colour due to the presence of respiratory pigment, haemoglobin and erythrocruorin dissolved in plasma. Blood corpuscles absent. Excretory system ---- Nephridia are the chief excretory organs. Other excretory organs include parapodia and botryoidal tissue. Excretory products are ammonia and urea in aquatic and terrestrial forms respectively.
  7. Nervous system --- Nervous system involves the presence of many ganglia. The two ganglia of a segment are connected to the double ventral nerve cord by lateral nerves. Reproduction - Asexual reproduction through fission, budding and regeneration. Sexual reproduction occurs with external fertilization. Females are oviparous. Development - Is direct or indirect through the involvement of trochophore larva. Cleavage holoblastic and spiral. E.g. Pheretima posthuma PHYLUM MOLLUSCA: Unsegmented, bilaterally symmetrical, triploblastic animals with organ system level of organization showing tube-with-in-a-tube body plan. Body of a typical mollusc is divided into three parts - -- head, foot and visceral hump. Presence of mantle or pallial cavity is evident. Body wall composed of ciliated epidermis and unstriated muscles present in bundles. External shell is present secreted by mantle and mostly composed of calcium carbonate. Schizocoel usually present, hence molluscs are truly coelomates. Cephalization distinct. However in cephalopods, head is fused with foot. Digestive system with alimentary canal and digestive glands present. Radula present in many members which act as rasping organ. Respiration takes place with the help of feathery gills or ctenidia, pulmonary sac, mantle and even epidermis. Open type of circulatory system present. Blood with a copper containing respiratory pigment called haemocyanin. Excretion with the help of sac-like kidneys called metanephridia. Other types of excretory organs include Organ of Bojanus, Keber's organ, nephridia and gills. Nervous system with ganglia which are joined by connectives and commissures. Sexes are separate with internal or external fertilization. Females are oviparous and ovoviviparous. Development direct or indirect with several larval stages.
  8. Pila globosa PHYLUM ECHINIDERMATA: Exclusively marine members exhibiting a variety of body shapes --- star-like, cylindrical etc. Larva with bilateral symmetry while adults possess radial symmetry and of pentamerous type. Presence of triploblastic condition with tube-within —a tube plan is a characteristic feature. True coelom occurs in echinoderms with coelomic fluid which helps in transport. Cephalization absent. Presence of microscopic tube feet on the under surface of the body is an important feature. Tube feet take part in locomotion and respiration. Echinoderms possess both exoskeleton and endoskeleton. Endoskeleton consists of calcareous plates or ossicles while exoskeleton consists of spines. Spines provide animals from predators. Complete digestive system with carnivorous mode of feeding. Respiration occurs with the help of respiratory tree, tube feet or peristomal gills. Open type of circulatory system with absence of heart and respiratory pigment. Blood vessels do not have a definite wall. Excretion occurs partly by diffusion through body surface and partly through dermal branchiae. Amoebocytes also take part in excretion in some species. Ammonotelic animals. Reduced nervous system with absence of brain. Sensory system is poorly developed and include photoreceptors, tentacles and statocysts. Nervous system reduced with absence of brain and presence of radial nerve cords. Asexual reproduction through autotomy and regeneration. In sea cucumbers body viscera and part of respiratory tree are vomited in order to ward off the predators. This process is known as evisceration. Lost body parts are slowly regenerated. Sexual reproduction involves external fertilization with indirect development. E. g. Asterias rubens

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