NEET Biology Notes Animal Kingdom Phylum-Porifera
Phylum-Porifera has primitive multicellular animals with cellular grade of organisation. Study of sponges is known as Parazoology. Free-living mostly marine either solitary or colonial. Body with a large number of incurrent pores called ostia leading into a spongocoel through a system of canals. Spongocoel opens out side by one or two large excurrent pores called oscula. Canals and spongocoel are lined by flagellated cells called choanocytes or collar cells. Proterospongia is a connecting link between Protozoa and Porifera. Sensory and nerve cells are absent in sponges.
Body wall with two layers of loosely arranged cell and a mesenchyme is present between them. Body has an endoskeleton made up of spicules, composed of calcareous or siliceous spicules or spongin fibres. Digestion is intracellular and holozoic. Respiration and excretion occur by simple diffusion. Reproduction is by asexual (external or internal buds) or sexual methods. Gemmules are the mass of archeocytes.
Body is cylindrical and radially symmetrical. Porocytes are special cells for passage of incoming water. Outer layer of cells is called pinacoderm made of pinacocytes.
A mesenchyma is found in between the two layers containing free amoebocytes and skeletal elements. Different types of amoebocytes are as follows :
Choanocytes or collar cells maintain water current and ingest the food particles. Leucosolenia has asconoid type of canal system. Nutrition is holozoic and digestion is intracellular. Food vacuole is transferred to amoebocytes and digestion is completed there. The chief nitrogenous waste of the sponge is ammonia.
Leucosolenia reproduces asexually by external budding and sexually by syngamy. No special gonads, sperms and ova are developed from archaeocytes.Fertilisation is internal. Cleavage is equal and holoblastic. Parenchymula larva swims freely and get attached to substratum.
It has radially symmetrical, diploblastic multicellular animals with a tissue grade of organisation. The members of this phylum are freshwater or marine, solitary or colonial forms, which may be free-swimming or sedentary. Body has a mouth at the oral end, which leads into a spacious cavity called gastrovascular cavity or coelenteron. The presence of long, hollow structures called tentacles used for locomotion and food capturing.
The epidermis consists of epitheliomuscular cells (provide musculature), cnidoblasts, interstitial cells (totipotent cells), nerve cells and sensory cells. The presence of peculiar type of cells is called cnidoblasts, nematocysts or stinging cells, in the ectoderm, especially in the tentacles, is used for offence and defence. Digestion is both intracellular and extracellular. Respiration and excretion by simple diffusion. The presence of a network of nerves spread all over the body.
Many forms exhibit polymorphism. Different types of individuals are present in a colony for different functions. These individuals are called zooids. Reproduction are either asexual (by external budding) or sexual (formation of gametes). Metagenesis is the alternation of two phases, i.e. polypoid and medusoid phases, e.g. in life cycle of Obelia.
It was discovered by Trembley in 1744. Linnaeus (1758) gave the name Hydra. It is diploblastic and radially symmetrical. Separate coelom is absent in Hydra, so can be called acoelomate. It has tissue grade of organisation with division of labour. ‘
Body cavity of Hydra is called coelenteron or gastrovascular cavity. Nematocyst plays an important role in locomotion, food capture, for offence and defence. It is carnivorous. It has no anus. Digestion in Hydra is first extracellular and then intracellular. It has nerve cells but no nerves. Reproduction is both asexual and sexual. No free larval stage (only a planula-like stage) occurs in Hydra. In the development of Hydra, there is no moulting or ecdysis.
It is bilaterally symmetrical, triploblastic true multicellular animals with organ grade of organisation. Free living (aquatic or terrestrial) but mostly parasitic (ecto or endoparasites). Body is dorso-ventrally compressed and leaf-like. A body cavity is absent. Space between body wall and alimentary canal is filled with mesenchyme (connective tissue).
Digestive system is incomplete and anus is absent. Respiration occurs by simple diffusion. Excretion with the help of specialised cells called flame cells or solenocytes. Nervous system is ladder-like consisting of a brain and a pair of longitudinal nerves connected by many transverse nerves.
Reproduction is usually by sexual methods. Majority of the forms are bisexual. Development is direct or indirect. Body is triploblastic. They have blind sac body plan.
The Fasciola hepatica (liver flukes) inhabit in the liver and bile ducts of different vertebrates like cattle, goat, rabbit, pig, dog and human.
It is an endoparasite and completes its life history in two hosts. The vertebrate sheep act as its primary host and mostly gastropod snail limnaea tranculata, as intermediate host. The broad anterior portion of animal bears a distinct triangular projection called the head lobe or oral cone. This structure bears mouth at its anterior tip, which is some what surrounded by the muscular oral sucker.
On the ventral side, at some distance from oral sucker, one more sucker is present called ventral sucker or posterior sucker of acetabulum. Both the suckers are the structures containing radial muscles.
In between the acetabulum and the oral sucker (i.e. mid ventrally), an opening is present called gonopore or genital opening. This opening is nearer to the acetabulum as compared to oral sucker. During breeding season, a temporary opening called opening of Laurer’s canal is seen on the dorsal surface, a little upwards to the middle of body.
Due to its parasitic mode of life, liver fluke is practically anaerobic or anoxybiotic in nature.
The animal is hermaphrodite or monoecious and male as well as female genital ducts open into a common chamber called genital atrium. The male reproductive system consist of two testes, one pair of vas deferens, seminal vesicle, an ejaculatory duct on a penis. The female reproductive system contains an ovary with its oviduct, vitelline glands with their ducts and yolk reservoir, shell glands, ootype, vitelline duct, uterus and the female genital pore.
The fertilisation is internal and takes place at the distal end of oviduct.
The life cycle of liver fluke passes through the following developmental stages :
The parasite attains sexual maturity and starts laying eggs in about 11-13 weeks after is its entry into the body of vertebrate host. The symptoms of liver rot (acute fascioliasis) caused by the fluke are more acute in lambs than in sheeps and appear about one month after the infection.
Animals which are mostly parasitic (in animals and plants) and few free-living forms present. Body is long, cylindrical, fusiform (pointed at both the ends). Body wall is composed of cuticle, epidermis and musculature. The presence of a false body pseudocoelom not lined by mesodermal epithelium. Digestive system is complete and respiration by simple diffusion.
Nervous system consists of a nerve ring and many longitudinal nerve cords. Only sexual reproduction is present. Males are usually shorter than females, e.g. Ascaris (roundworm, a parasite, faculatative aerobic), Rhabditis (free-living), Dracunculus (guinea worm), Enterobium (pinworm), Trichiuris (whip worm), Wuchereria (filarial worm), Loa loa (eye worm).
Ascaris, roundworm present in the most common endoparasite in the small intestine of childern. Male is smaller than female with curved tail, two pineal setae (copulatory organs) and cloaca. The epidermis of Ascaris is syncytial. The body cavity of Ascaris is pseudocoel.
Excretory system consists of a single excretory cell or renette cell. Ascaris is monogenetic, only one host is required for the development. The larva is called rhabditiform. Ascaris causes the disease ascariasis.
Wuchereria bancrofti (filarial worm) is the cause of elephantiasis and widely distributed in tropical countries. The diseases is characterised by the symptoms like headache, anaemia, fever, lymphatic tumours, swelling in limb, etc.
It is free-living, terrestrial or aquatic form animal (freshwater or marine). Body is long, cylindrical and metamerically segmented. Body wall consists of cuticle, epidermis and musculature. Body cavity is a true coelom, lined by mesoderm. Digestive system is complete. Respiration is either through skin or through gills. Excretion with the help of characteristic nephridia. Chloragogen cells or yellow cells of earthworm are analogous to vertebrate liver cells. The presence of a circulatory system (closed type). Haemoglobin dissolves directly in tb’ dasma.
Nervous system consists of a nerve ring and a double ventral nerve cord with segmental ganglia. Locomotion with the help of setae or parapodia. Reproduction by sexual methods. Either unisexual or bisexual. Development may be direct or indirect. Body has a true coelom.