Question

Explain filter feeding of porifera and passage of water in sponges

Answer 1

Answer: Sponges belong to the phylum: porifera, as the name suggests they have pores all over the body. The pores are known as ostia. The body cavity of sponges is known as spongocoel, they are diplobastic animals with a very primitive multicellular structure with a cell aggregate body plan(no tissue system). They are sedentary in nature. Mostly found in marine environment, some members can be found in fresh water.

Ostia are inhalents and there is one large pore known as osculum.(some sponges like Euspongia show several large pores known as oscula). The osculum serves as the exhalant.

Sponges are filter feeders.Mainly feeding on bacteria and other food particles in water. The food is filtered through the water which enters through the ostia. The food is digested by special cells known as choanocytes or collar cells which are phagocytic.Amoebocytes,another important cells in sponges transfer the digested food or the nutrients to the other cells of the body. Besides this the choanocytes create the water current with the help of flagella for circulation of water.

The water enters the body of the sponges through ostia and passes through the interconnected canal system constituting a circulatory system. This canal system maintains a current of water throughout the body and provides food particles and oxygen to the cells and takes away carbon dioxide and the excretory products. The water is expelled through the osculum.

There are three types of canal systems observed in sponges

1. Ascon type: It is the simplest where ostia direcltly opens into the spongocoel and then water passes out through osculum.

2. Sycon type: In this the sponge wall is complicated with various types of canals and pores which ultimately opens into spongocoel.

Eg. Water enters through dermal ostia(porocyte) goes to incurrent canal then to radial canal then to excurrent canal then to the spongocoel and then outside through osculum.

3. Leucon type: In this the wall is thick and complicated. There are flagellated chambers formed by radial canals. Incurrent canals are branched. Eg.Water enters through dermal ostia(porocyte) goes to incurrent canal then to flagellated chambers then to excurrent canal then to the spongocoel and then outside through osculum