Characteristics and structure of phylum porifera

Characteristics of phylum porifera: The porifera are sponges. They are primarily marine animals and there are nine thousand species of sponges. Their body consist of loosely organized cells and they vary in size less than a centimeter to a mass that can fill your arm. They have simple body structure no tissues no organs. They are asymmetrical. They have three cell types : pinacocytes, mesenchymal cells and choanocytes. They have central cavity. This cavity consist of series of branching chambers and water circulates through there chambers. Numerous pores are present in body wall. These pores are called ostia and osculum. Their skeleton is composed of spicules. They have no nervous system but neurosensory cells are present in them. Asexual reproduction in porifera are takes place by budding. They are hermaphrodites (both sexes in one individual) and larvae are produced during development. They capture food particles from water and use choanocytes to capture suspended particles. Oxygen diffuses through body wall. They have external fertilization and release gametes into water column. They attached to substrates and ability to regenerate lost parts. Show symbiotic relationships with host algae, bacteria or other organisms. Sponges can recognize foreign particles. sponges filter vast amounts of water. Their food source are various marine animals. Some species have eyes. Some sponges live up to 2300 years. They can survive in extreme conditions.                                                                                                                                                      Structure of phylum porifera: They have simple body. Sponges are consist of specialized cells. Three types of cells are present in them. Pinacocytes: These are thin walled and flat cells and line the outer surface. Pinacocytes are slightly contractile. Their contraction can change the shape of some sponges. Some pinacocytes forms tube like contractile porocytes and this tube like porocytes regulate water circulation. The openings of porocytes are pathways for water movement of water through body wall. Mesenchymal cells: Mesohyl is jelly like layer present below the pinacocytes contain amoeboid cells in it and these cells are called mesenchymal cells. They freely move in mesohyl. These cells are specialized for reproduction, secreting skeletal elements, transporting and storing food and forming contractile rings around the openings in sponge wall. Choanocytes: They are present below the mesohyl and form the lining of the inner chamber. Choanocytes are flagellated cells. They have a collar like ring of microvilli surrounding a flagellum and microfilaments connect the microvilli. It forms a netlike structure within collar. The flagellum creates water currents through the sponge. The collar filters microscopic food particles from water. Skeleton of sponges: There are two types skeleton in sponges. Spicules: These are consist of microscopic needlelike spikes. spicules are formed by amoeboid cells. They are made up of calcium carbonate or silica. They have different shapes. They provide structural support and protection. Spongin fibers: The spongin fibers are made up of spongin. Spongin is fibrous protein made up of collagen. They provide flexibility and elasticity. They also provide defense against predators.