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INTRODUCTION Phylum Porifera is the simplest and is considered the most primitive of the multicellular animals NAME The word Porifera is derived from LatinPorus means pore and ferra means to bearSothe Poriferas are pore-bearing animalscommonly called the sponges HABITAT All Poriferas are aquaticOut of total 5000 species150 species live in fresh water while all others are marine SIZE The Poriferas range in size from few millimeter wide to more than one meter tallThey are macroscopic ie can be seen with naked eyeScolymastra joubini-a barrel like glass sponge of Antarctica is more than a metre tall COMPOSITION These animals are composed of many cellshoweverthere is no tissue organization and have no organsSponges lack symmetry In most spongesthe body wall is formed of 1an outer layerpinacodermmade up of cells called pinacocytes and 2an inner layerchoanodermmade of flagellated collar cells called choanocytes Between these two layers is present gelatinous mesenchyme which may contain amoeboid cells and spicules or sponginfibres Penetrating the pinacoderm are cylinderical cells called sporocytes BODY CAVITY There is a single cavity inside the bodythe spongocoelIn most sponges this spongocoel may be divided into flagellated chambers or canalslined by flagellated choanocytes CIRCULATION AND RESPIRATION Numerous pores are present in the body wallThe pores through which water enters the body are called ostia and pore through which the water leaves the body is known as osculummain openingThere are no respiratory or circulatory organs NUTRITION Since the sponges are sessilethereforethese depend upon the food coming to them along with water currents brought about by movement of flagella of choanocytesThe food includes small animals called zooplankton and plants called phytoplankton which constitute about 20 of thier food 80of thier food consists of detrital organic particlesThe food enters the spongocoel cavity through ostiaThe food is ingested by the flagellated cellsthe choanocytesThe waste products either diffuse out of the sponge directly through the body wall or flow out through osculum LOCOMOTION The adult sponges are stationaryspending their lives attached to
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