Porifera, Coelenterata, Ctenophora

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2 Porifera, Coelenterata, Ctenophora Contents Animal Classification - Flow Chart... 3 Phylum Porifera... 4 Phylum Cnidaria Phylum Ctenophora

3 Animal Classification - Flow Chart Kingdom Level of Organisation Symmetry Cellular Level Asymmetrical Porifera Animalia Radial Cnidaria Ctenophora Tissue/Organ System Acoelomates Pseudocoelomates Platyhelminthes Aschelminthes Bilateral Annelida Arthropoda Coelomates Mollusca Echinodermata Hemichordata Chordata 3

4 Phylum Porifera Phylum Porifera includes pore-bearing animals. They are also called sponges. There are about 10,000 living species of sponges. The animal nature of sponges was studied and explained by Ellis. The term Porifera was coined by Robert Grant. 1. Habitat Found in water from low-tide areas to a depth of 5,000 metres. Sponges are sessile. 2. Shape Cylindrical, vase-like, globular, flat, irregular 3. Symmetry Radially symmetrical or asymmetrical 4. Germ Layers Diploblastic 5. Level of Cellular level of organisation Organisation 6. Body Surface Body has a number pores called ostia. 7. Body Wall Body wall is made of three layers: 4

5 Pinacoderm Outermost dermal layer made of pinacocytes and porocytes. Choanoderm Inner gastral layer made of choanocytes or collar cells. Mesohyal It is a non-cellular layer between the pinacoderm and choanoderm. It contains spicules, spongin fibres and amoebocytes modifed into various forms to perform different functions. 8. Spongocoel The central cavity called spongocoel open outside through the osculum. 9. Canal System In the canal system, the water current enters through ostia, passes through the spongocoel and exits the body through the osculum. In sponges, the canal system is meant for food gathering, respiration and removal of waste. Four types of canal systems are in sponges: 5

6 Asconoid Canal System Syconoid Canal System Leuconoid Canal System Rhagon Canal System 10. Nutrition Nutrition in sponges is holozoic, and food particles are collected by the choanocytes by the water current. 11. Excretion and Occurs by diffusion. Respiration 12. Skeleton It is made of calcareous spicules or spongin fibres. 13. Reproduction Sponges are hermaphrodites. Reproduce asexually by fragmentation and sexually by the formation of gametes. Fertilisation is internal. Development includes the larval stage called amphiblastula. 14. Regeneration Sponges have a great ability of regeneration. Fragments or even isolated individuals can give rise to a complete sponge. 6

7 Sponges are the only animals without sensory cells and nerve cells. Choanocytes are specialised cells. Presence of choanocytes is an exclusive feature of Phylum Porifera. They are flagellated cells and line the spongocoel. The incessant beating of flagella maintains the continuous flow of the water current in the spongocoel. Classification of Phylum Porifera Calcarea Hexactinellida Desmospongia o They are deep sea sponges with a cup-shaped or vaselike body. o Marine sponges with a simple structure. o Skeleton is made of calcareous spicules. o Examples: Leucosolenia o Skeleton is made of 6-rayed siliceous spicules. o Examples: Euplectella (Venus flower basket) o Marine sponges with a cup or vase-like body. o Exception is Spongilla which is a freshwater sponge. o Skeleton is made of oneor four-rayed siliceous spicules. o Examples: Euspongia (Common bath sponge) 7

8 o Scypha o Hyalonema (Glass-rope sponge) o Spongilla (Freshwater sponge) Economic Importance of Sponges: Sponge skeleton is used as a packing material. Sponges are used for cleaning glass in the glass industry. Sponges are used for washing floors and walls. They provide refuge to various small animals such as coelenterates, worms and small crustaceans. They are also used as padding for sound absorption. 8

9 Luffa sponge is not a sponge but a gourd. When the gourd is dried, its skeleton made of its fibrous material resembles the sponge. The Luffa sponge is used for scrubbing. 9

10 Phylum Cnidaria Phylum Cnidaria includes 10,000 species. The old name of this phylum is Coelenterata. Peyssonnel and Trembley reported the animal nature of coelenterates. The term Coelenterata was coined by Leuckart. Hatschek coined the term Cnidaria. 1. Habitat Aquatic mostly marine. Only hydra is a freshwater form. Coelenterates are either sessile (Example: Hydra) or free-swimming (Example: Sea anemone). 2. Symmetry Radial symmetry. 3. Germ Layers Coelenterates are diploblastic. They show the outer epidermis (ectoderm) and inner gastrodermis (endoderm). 4. Level of Coelenterates show tissue-level organisation. Organisation 5. Body Wall Outer epidermis consists of various kinds of cells such as cnidoblasts, nematocysts, nerve cells and sensory cells. Inner gastrodermis consists of digestive cells, gland cells, nerve cells and sensory cells. 6. Gastrovascular Endodermis encloses a cavity called the gastrovascular cavity. Cavity The opening of the gastrovascular cavity is called mouth or hypostome which is terminal and surrounded by many tentacles. This cavity helps in extracellular digestion. 7. Digestion Cnidarians are carnivorous animals. Digestion is extracellular and intracellular. Extracellular digestion occurs in the gastrovascular cavity. Intracellular digestion occurs in the digestive cells of the gastrodermis. 8. Excretion and Excretion and respiration are through the body surface by diffusion. Respiration 9. Nervous System Consists of a network of cells. Statocyst, an organ responsible for balance, was first developed in cnidarians. 10. Skeleton Some cnidarians show the presence of calcareous exoskeleton or endoskeleton. Example: Corals show an exoskeleton made of calcium carbonate. 11. Body Forms There are two basic body forms in cnidarians. 10

11 Polyp Sedentary, cylindrical forms. Mouth and tentacles are at the free end. Sense organs are absent. Asexual phase of the life cycle. Medusa Free-swimming, umbrella-shaped. They bear gonads. Sense organs are present. Sexual phase of the life cycle. 12. Reproduction Asexual reproduction is by budding. Sexual reproduction is by the fusion of male and female gametes. 13. Development In sexual reproduction, the development is indirect through the planula larva. 14. Metagenesis Cnidarians such as Obelia show metagenesis or alternation of generation. Polyps reproduce medusa asexually, and medusa produce polyps sexually. Both polyps and medusae are the diploid phases. 11

12 15. Polymorphism In colonial cnidarians, polyp and medusae occur in different forms to carry out special functions. This phenomenon is called polymorphism. Such forms are call zooids. There are three kinds of zooids: Gastrozooids (For feeding) Blastozooids (For reproduction) Dactylozooids (For defence) Hydra possesses the ability of regeneration if its fragment contains a part of epidermis and gastrodermis. It was discovered by Abraham Trembley. 12

13 Cnidoblasts are the stinging cells of cnidarians found around the mouth and on the tentacles. Each cnidoblast has a nematocyst filled with hypotoxin. Hypotoxin is a poisonous fluid which paralyses the prey. The anterior end of the nematocyst has a shaft which contains a long threadlike structure. When stimulated, the nematocyst is ejected and the long thread injects hypotoxin into the body of the prey. Classification of Phylum Cnidaria It includes three classes: Hydrozoa Scyphozoa Anthozoa o Marine but a few species are found in freshwater. o Exclusively marine animals. o Exclusively marine animals. o Both polyp and medusa occur in the life cycle. o Only medusae are the body forms. o Only polyps are the body forms. Polyps are the dominant phase of the life cycle. o Mesoglea is non-cellular. o Mesoglea is cellular. o Mesoglea contains cells and fibres. o Examples: Hydra o Examples: Aurelia (Jelly fish) o Examples: Sea anemone 13

14 o Obelia o Rhizostoma o Corals o Physalia o Gorgonia (Sea Fan) Economic Importance of Cnidarians: Calcareous material of corals can be used for building purposes. Red corals are used for making jewellery and ornaments. Corals are also used as decorative pieces. 14

15 The Great Barrier Reef, Australia, has coral reefs of about 900 miles long. It is a stable marine ecosystem which supports a variety of animal and plant life. 15

16 Phylum Ctenophora Phylum Ctenophora includes 50 species. These animals were earlier placed in the phylum Cnidaria but later separated in different phylum because of lack of cnidoblasts. Phylum Ctenophora was first recognised by Escscholtz. 1. Habitat Exclusively marine. Solitary, free-swimming or pelagic. Ctenophores are highly active animals. 2. Symmetry Biradial symmetry. 3. Germ Layers Diploblastic animals having outer ectoderm and inner endoderm. 4. Level of Ctenophores show tissue-level organisation. Organisation 5. Body Wall Outer epidermis of tentacles consists of colloblasts which help to capture food. Nematocysts are absent. Mesoglea does not contain amoebocytes but fibres and smooth muscle cells. 6. Coelom Ctenophores are acoelomates. 7. Locomotion Ctenophores bear cilia which are arranged in eight external rows called comb plates. These cob plates help in locomotion. 16

17 8. Digestive Tract Digestive tract is complete. It consists of mouth, stomodaeum, stomach, anal canals and anal pores. Digestion is both extracellular and intracellular. 9. Nervous System Consists of diffused network of cells. 10. Sense Organs Statocyst for equilibrium is present at the aboral end. 11. Excretion and Occur through the general body surface. Respiration 12. Skeleton System Absent 13. Reproduction Asexual reproduction is absent. Ctenophores are hermaphrodites. Fertilisation is external. 14. Development Development is direct without any larval stage. In some forms, immature ciliated cydippid larva is found. 15. Bioluminescence It is the property of living organisms to emit light. It is commonly seen in ctenophores. Classification of Phylum Ctenophora Phylum Ctenophora consists of two classes. Tentaculata o Tentacles are present o Example: Pleurobrachia Nuda o Tentacles are absent. o Example: Beroe 17