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Porifera

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Information about Porifera
Science-Technology

Published on October 25, 2010

Author: rkpillai

Source: authorstream.com

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Phylum Porifera : Phylum Porifera Dr. R. K Pillai, Dept of Zoology, Hindu College, Moradabad mail.rkpillai@gmail.com Pre-Medical Presentation Diversity in Living World Slide 2: 1. Number of living species about 5,500. 2. The phylum ‘Porifera’ (L., porus, pore, ferre, to bear) contains those animals commonly called sponges. 3. Sponges are the metazoa lacking true embryological germ layering (so the term diploblastic is improper for sponges). 4. Porifera is the only phylum in the subkingdom of animals named Parazoa. 5. Sponges exhibit cellular level of construction without true tissues. 6. Sponges are “multicellular grade” organisms with cell aggregate body plan. 7. Adult sponges are asymmetrical or superficially radially symmetrical in form. 8. Sponges were mistaken for plants, as sponges are sessile and immobile. Some freshwater species are green as they contain photosynthetic algae. Slide 3: 9. An English naturalist John Ellis (1765) established the animal nature of sponges. 10. The phylum name ‘Porifera’ was coined by Scottish naturalist Robert E. Grant, (1836). 11. All sponges are aquatic, mostly marine and few freshwater forms. 12. Sponges may be solitary (e.g., Sycon) or colonial (e.g., Leucosolenia). 13. All adult sponges are sessile attached to submerged rocks or other hard substratum. 14. Though tissues are absent there is some physiological division of labour among the cells of sponges. 15. Body wall is with outer pinacoderm, inner choanoderm and gelatinous matrix called mesenchyme (mesohyl) in between. 16. Mesenchyme is the “connective tissue” of sponges consists of skeletal elements, fibrils and free amoeboid cells. 17. The cavity common to all sponges is spongocoel or paragastric cavity lined with, flagellated choanocytes. 18. Choanocytes or collar cells are present only in sponges. Slide 4: Sponge anatomy Slide 5: 19. Sponges have numerous mouthlets (ostia) and one exit (osculum). 20. If carmine particles are placed close to osculum of a living sponge, these will be carried away. 21. Sponges have a canal system also called aquiferous system and they need a continuous current of water flowing through their bodies for respiration, excretion, nutrition and reproduction. 22. Most sponges fall into one of three types of canal systems: asconoid, syconoid or leuconoid. 23. Rhagon type is found in few sponges during larval stage. This will be transformed to leuconoid type during adulthood. 24. The simplest type of canal system in Porifera is asconoid type. 25. Sponges usually have a skeleton consisting of spicules or spongin fibres. 26. Spicules of sponges may be either calcareous or silicious. 27. Skeleton of sponges is secreted by scleroblasts. Three types of scleroblasts are: calcoblasts, silicoblasts and spongioblasts. (Collencytes and lophocytes secrete large quantities of collagen). 28. Adult sponges are sessile suspension feeders; larval stages are motile. Canal Systems in Sponges : Canal Systems in Sponges Slide 8: 29. Food coming through the incoming water is ingested by choanocytes. 30. Digestion in sponges is intracellular like protozoans. 31. Digestion of food takes place partially in choanocytes and partially in wandering amoebocytes. 32. Excretion (primarily ammonia) and gas exchange are by simple diffusion occurs across the choanoderm. 33. Most sponges are hermaphroditic. Reproduction is asexual or sexual. 34. Asexual reproduction is either by fragmentation or through the production of gemmules or buds. 35. Gemmules are internal buds containing archaeocytes, mostly produced by freshwater sponges of the family Spongillidae, concerned with asexual reproduction. 36. Sex cells (sperm and ova) arise from undifferentiated archaeocytes at different times, protogyny or protandry. 37. Fertilization and early development are typically internal. 38. Three larval stages have been found in sponges: "coeloblastula" larvae (="blastula" larvae), parenchymula larvae (= parenchymella larvae) and amphiblastula larvae. Slide 10: Sponge spicules Slide 11: 39. Sponges have great regenerating power due to archaeocytes which are highly totipotent cells. 40. Olynthus is a name for a solitary hypothetical ancestral sponge. 41. Recently a number of important bioactive compounds has been discovered in sponges, many having potential pharmacological significance (e.g., antimicrobial, anti- inflammatory, antitumor, and cytotoxic compounds). 42. The discovery of these natural products has led to a renewed interest in sponges. Classification : Classification The living Poriferans are divided into three classes on the basis of their skeletal structures. Class I Demospongiae (Gr., demos, people; spongos, sponge) Class II Calcarea (L., calcis, lime) or Calcispongiae (Limy sponges) Class III Hexactinellida (Gr., hex, six; aktis, ray; -ellus, dim) or Hyalospongiae (Glass sponges) Class I Demospongiae : Class I Demospongiae The largest class of sponge, comprising about 95 per cent of the living species. Mostly marine, few freshwater forms, skeleton mostly spongin fibres, leuconoid canal system, Rhagon larva. e.g., Spongilla, a freshwater sponge Cliona, boring sponge, harmful to oyster industry Euspongia, bath sponge Best commercial sponges belonging to the genera Hippospongia and Spongia are found in warm shallow water of Mediterranean and Florida. Slide 14: Spongilla Cliona Euspongia Class II Calcarea : Class II Calcarea All marine, inhabits shallow water. Skeleton calcareous spicules. Canal system asconoid (ascon) or syconoid (sycon) type. e.g., Leucosolenia, Sycon, Clathrina and Grantia Slide 16: Leucosolenia Sycon Grantia Clathrina Class III Hexactinellida : Class III Hexactinellida Exclusively marine, inhabits deep water. Skeleton siliceous six-rayed spicules. External pinacoderm absent and replaced by a noncellular dermal membrane. Choanocyte layer may be syncytial. e.g., Euplectella (Venus’ flower-basket). Famous for beauty of skeleton, a traditional wedding gift in Japan, shows commensalism with shrimps of the genus Spongicola, The male female pair of shrimp spend their lives as “prisoners of love". Slide 18: Euplectella Pheronema Hyalonema Slide 19: It is a symbol of the lifetime bond between two partners. Hyalonema (Glass-rope sponge), Pheronema (Bowl sponge) Ephydatia is the best-studied sponge genus in the world. The first experiments on sponge regeneration were performed on Microciona prolifera during the early 1900s. Corticium, Plakina and Plakortis are unusual sponges. These have no supporting skeleton, lacking both spicules and spongin fibres. Cladorhiza is a deep sea sponge which lack choanocytes and canal system. It feeds as carnivore passively entrapping small crustaceans. LEUCOSOLENIA : LEUCOSOLENIA 1. Leucosolenia belongs to the class Calcarea of the phylum Porifera. 2. Leucosolenia is sessile, colonial and marine. 3. Leucosolenia is found in shallow water. 4. It is an asconoid sponge with simplest and most primitive structural plan. 5. Body of Leucosolenia is cylindrical and radially symmetrical. 6. The body cavity of Leucosolenia is called spongocoel or paragastric cavity. 7. Single large upper opening is called osculum (exit). 8. The body wall has numerous minute pores called ostia, correspond to mouthlets. 9. Porocytes are special cells for passage of incoming water. 10. Outer layer of cells is called pinacoderm made of pinacocytes. Leucosolenia: Body wall : Leucosolenia: Body wall Slide 22: 11. Inner layer of cells is choanoderm which lines the spongocoel. 12. A mesenchyme is found in between the two layers containing free amoebocytes and skeletal elements. 13. Different types of amoebocytes are: Archaeocytes – undifferentiated totipotent cells Chromocytes – with pigment granules. Thesocytes – with reserve food granules Myocytes – highly contractile, spindle-shaped cells Trophocytes – supply nutrients to developing cells (nurse cells) Gland cells – secrete slimy substance Sex cells – develop from archaeocytes only during breeding season 14. Myocytes form sphincters around osculum and ostia. 15. Choanocytes are collar cells or flagellated cells. They maintain water current and ingest the food particles. 16. Spicules are embedded in mesenchyme. Three different types of spicules present in Leucosolenia are monaxons, triradiates and tetraradiates. 17. Spicules of Leucosolenia are made up of calcium carbonate, secreted by calcoblasts. Slide 23: 18. Leucosolenia has asconoid type of canal system. 19. The path of water current in Leucosolenia is: Dermal ostia—gastral ostia—spongocoel—osculum. 20. Nutrition is holozoic and digestion is intracellular. 21. The food is constituted by protozoans, diatoms, bacteria, etc., coming in with water current. 22. Choanocytes ingest food particles in the form of food vacuoles, probably by means of pseudopodia. 23. Food is partially digested by means of certain enzymes in choanocytes. 24. Food vacuole is transferred to amoebocytes and digestion is completed there . 25. The chief nitrogenous waste of the sponge is ammonia. 26. Leucosolenia reproduces asexually by external budding and sexually by syngamy. 27. Leucosolenia is monoecious, i.e., male and female reproductive cells or gametes are formed in the same individual. 28. No special gonads, sperms and ova are developed from archaeocytes . Slide 24: 29. Fertilization is internal. 30. Cleavage is equal and holoblastic. 31. Zygote develops into a hollow blastula called coeloblastula. 32. Further development results in the formation of stereogastrula or parenchymula larva. 33. Parenchymula swims freely and get attached to substratum, finally developing into an adult sessile sponge. 34. The corresponding stages in another sponge Scypha (Sycon) are stomoblastula and amphiblastula. 35. Leucosolenia has a free swimming larval stage, but the adult is sedentary. Taxonomic Summary : Taxonomic Summary Phylum Porifera — The Sponges Subphylum Cellularia (all members possess distinct choanocytes) Class Demospongiae Cliona — Boring sponge Chalina —Mermaid gloves (Dead man's fingers) Spongilla —Freshwater sponge Euspongia — Bath sponge Poterion — Neptune's goblet Hippospongia — Horse sponge Hircinia — Horny sponge Slide 26: Class Calcarea — the limy sponges Scypha — Urn sponge Subphylum Symplasma (epithelial and "choanocyte" tissues are syncytial) Class Hexactinellida — the glass sponges Pheronema — Bowl sponge Hyalonema — Glass-rope sponge Euplectella — Venus' flower-basket Slide 28: End Thanks

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