Page 9 - 11-Bio-10 Kingdom plantae

10. Kingdom Animalia eLearn.Punjab

The Porifera are pore-bearing animals, commonly called the sponges. All are aquatic. Out of total
5000 species 150 species live in fresh water while all others are marine.

General Characteristics

These animals are composed of many cells however there is no tissue organization and have
no organs. Sponges lack symmetry. In most sponges the body wall is formed of an outer layer,
pinacoderm, made up of cells called pinacocytes: and an inner layer choanoderm made of flagellated
collar cells called choanocytes. Between these two

Scolymastra joubini- a barrel like glass sponge of

layers is present gelatinous mesenchyme which may Antarctica is more than a metre tall.
contain amoeboid cells and spicules or sponging fibres.

The poriferans range in size from few millimeter wide to more than one metre tall. They are
macroscopic i.e., can be seen with naked eye. There is a single cavity inside the body, the spongocoel.
In most sponges the spongocoel may be divided into flagellated chambers or canals, lined by
flagellated choanocytes.

Numerous pores are present in the body wall. The pores through which water enters the body are
called ostia, and pore by which the water leaves the body is known as osculum (main opening).
There are no respiratory or circulatory organs.

Since the sponges are sessile, therefore these depend upon the food coming to them along with
water currents brought about by movement of flagella of choanocytes. This includes small animals,
(zooplankton) and plants, (phytoplankton) which constitute about 20% of their food. 80% of their
food consists of detrital organic particles. The food enters the spongocoel cavity through Ostia. The
food is ingested by the flagellated cells, the choanocytes. The waste products either diffuse out of
the sponge directly through the body wall or flow out through osculum.

The adult sponges are stationary, spending their lives attached to the rocks at the bottom or other
solid objects. However, their larvae are able to move (swim).

There is no definite nervous system, however neurosensory and neuron cells are probably present
which seem to coordinate the flow of water.

The skeleton is in the form of variously shaped needle-like structures called spicules. These may be
calcareous or siliceous. The bath sponge has a skeleton of spongin fibres. The skeleton is present
among pinacocytes and provides support. Spicules are also present around osculum and ostia.

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