Fonte: www. Elas abundam em todos os mares, onde quer que as rochas, conchas, madeiras submersas ou corais providenciem um substrato adequado. Revestem a cavidade atrial e constituem a camada gastral. Entre as papilas aparecem os poros. Distinguimos dois tipos de canais: inalantes e exalantes. A esta classe pertence a maioria das esponjas.

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They are primarily marine animals. There are nine thousand species of sponges. There are following characteristics of the phylum Porifera: Their bodies consist of loosely organized cells.

They vary in size from less than a centimeter to a mass that can fill your arm. They are asymmetrical or radially symmetrical. They have three cell types: pinacocytes, mesenchyma cells, and choanocytes. They have central cavity or spongocoel. This cavity may be divided into series of branching chambers. Water circulates through these chambers for feeding. Numerous pores are present in the body wall. Skeleton is composed of spicules.

Nervous system is absent but neurosensory cells are present. Asexual reproduction takes place by budding. They are hermaphrodites and larvae are produced during development. But still sponges are more than colonies of independent cells. The sponges also have specialized cells. Therefore, division of labour is present in them. Following types of cells are present in phylum porifera. Pinacocytes: Pinacocytes are thin walled and flat cells. They line the outer surface of a sponge.

Pinacocytes are slightly contractile. Their contraction can change the shape of some sponges. Some pinacocytes forms tube like contractile porocytes. Porocytes regulate water circulation. The openings of the porocytes are pathways tiw water movement of water through the body wall. Mesohyl: Mesohyl is a jelly like layer present below the pinacocytes. Amoeboid cells are present in it.

These cells are called mesenchyma cells. The meseuchyma cells freely move in the mesohyl. These cells are specialized for reproduction, secreting, skeletal elements, transporting and storing food and forming contractile rings around openings in the sponge wall. Choanocytes: Choanocytes or collar cells are present below the mesohyl. They form the lining of the inner chamber. Choanocytes are flagellated cells. They have a collar like ring of microvilli surrounding a flagellum. Microfilaments connect the microvilli.

It forms a netlike structure within the collar. The flagellum creates water currents through the sponge. The collar filters microscopic lbod particles from the water. Collar cells arc also present in a group of protists called choanollagellates. Choanocytes are present in sponges and choantlagellaes.

It suggests an evolutionary link between these groups. Skeleton: The nature of the skeleton is an important characteristic in sponge taxonomy. There are two types of skeleton in sponges: a Spit lest The spicules consist of microscopic needlelike spikes Spic les are formed by amoeboid cells.

They are made of calcium carbonate or silica. They have different shapes. I Spongin fibers: The spongin fibers are made up of. Spongin is a fibrous protein made of collagen. It is dried, beaten and washed and all cells are removed. This washed and dried spongin produce a commercial sponge. Thechoanocytes organized to form water canal system. Water currents bring food and oxygen for a sponge.

It also carries away metabolic and digestive wastes. Water canal system is used for circulation and filtration of food. There are three principal types of water canal systems: 1. Ascon type It is simplest and least common sponge body form. Ascon sponges are vase like. Ostia are the outer openings of porocytes.

The porocytes open directly into spongocoel. Choanocytes line the spongocoel. The movements of flagella of choanocytes draw water into the spongocoel through the ostia. Water leaves the sponge through the osculum. Osculum is a single large opening at the top of the sponge.

Sycon type The sponge wall is folded in the sycon body form. Following canals are formed by the folding of its wall: a Incurrent canal: The invaginations of the body wall of sycon form incurrent canals.

Water enters into incurrent canal through dermal pores. Choanoeytes line the radial canals. The beating of flagella of choanocytes moves water through incurrent radial canals and spongocoel. It finally moves out the osculum.

Water path through sycon type: Dermal pore — incurrent canal — pore — radial canal — spongocoel — osculum. Leucon type Leucon sponges have an extensively branched canal system. There are following chambers in leucon type: a Branched incurrent canal: Water enters the branched incurrent canals through ostia b Choanocytes chamber: Incurrent canal lead into choanocytes-lined chambers. Therefore, spongocoel is absent in them. They have many oseulums for water leaving the sponge. Luecon type canal system is formed by the evolution of simple canal system.

Advantages of complex canal system Complex sponges have an increased surface area for choanocytes. Therefore, a large amount of water through the sponge.

It increases the filtering capability of sponges. Nutrition Food: Sponges feed on particles with size from 0. Their food consists of bacteria, microscopic algae, protists and other suspended organic matter. The preys are slowly drawn into the sponge and digested. Large populations of sponges play an important role in reducing the turbidity of coastal waters. A single leucon with size 1 cm in diameter and 10cm high can fitter 20 liters of water everyday.

A few species of sponges are carnivores. The deep-water sponges like Asbestopduma have spicules covered filaments. It captures small crustaceans with the help of these spiculces. Mechanism of feeding: Choanocytes filter small suspended food particles. Water passes through their collar near the base of the cell.

It then moves out of choanocytes into the sponge chamber through the open end of the collar. Suspended food is trapped on the collar.

It passes through microvilli and reaches at the base of the collar. It forms a food vacuole in collar. The pH of food is changed. Digestion in food vacuole takes place by lysosomal enzymes. Partially digested food is passed into amoeboid cells. Amoeboid cells distribute it to other cells. Pinacocyts lines the incurrent canal. Large food particles up to 50 pm can enter into pinacocytcs byphagocytosis. Sponges also absorb nutrients dissolved in seawater by active transport.

Excretion and respiration There is an extensive canal system in sponges.


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