A brief study and characteristic features of Phylum Porifera

Introduction

Porifers are the first multicellular animals present in nature. The word Porifera is derived from two Greek words Pori-pores; feran- bearing; means pore bearing organisms. The Phylum name Porifera was introduced by Robert E. Grant. The Phylum Porifera exclusively include multicellular primitive organisms called Sponges. The study of Sponges is known as Parazoology.Sponges are exclusively aquatic in their habitat and prefer to live in warm water rather than cold water. Phylum Porifera include 5,000 different species of sponges.

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Characteristic features of the animals of Phylum Porifera

1. Sponges are the only animals found in Phylum Porifera. Most of the Sponges are marine in habitat but a few species of fresh water sponges are also found in this Phylum. Family members of Spongilladae are fresh water in nature. Ex: Euspongia and Spongilla. Sponges are sedentary animals attached to some objects but their larval stages are active and free swimming. Sponges live singly or in colonies. Sponges are found attached to under water rocks, aquatic plants and aquatic animals like crabs and molluscs.

2. Phylum Porifera represents the first multicellular organisms in animal kingdom. Even though Porifers are multicellular organisms, these organisms don't show tissue grade level of organization as well as division of labor. Sponges shows cellular level of organization.

3. The most striking feature of the animals of this Phylum is the entire outer surface of the body of Sponges is covered by minute pores called Oostia or inhalent or incurrent pores. Towards the anterior end of a Sponge's body is provided with big opening called Osculum. Water along with food particles enters into the body through Oostia and the water exit to outside through Osculum.

4. Most of the Sponges exhibit asymmetrical body or but some radially symmetrical. The body wall of Sponges show an outer ectoderm and inner endoderm. A non-cellular gelatinous layer is present in between these two layers called mesenchyme. The body wall of Sponges is described as diploblastic as it consists of only two layers. The outer ectoderm layer include pinacocyte cells and the inner endoderm layer is made of choanocyte cells.

5. Porifers include a peculiar canal system in their body. The pathway entering and outgoing of water current in sponges is referred to as canal system. Water along with food particles enters through Oostia into the cavity of the Sponge's body and leaves through Osculum present at the anterior end of its body. Canal system in Sponges help in respiration, nutrition and excretion. It also helps to carry out reproductive elements.

6. The body of Sponges is provided with a hard outer exoskeleton. The skeleton is formed of calcareous or silicious spicules. Sometimes spongin fibres are present in between the cells of the body wall of Sponges which act as a skeleton. Spongin is a scleroprotein and which contain large quantity of iodine. Spicules are produced by amoeboid cells of Sponges body wall called scleroblasts. Spongin is produced by spongoblast cells of its body. Skeleton is absent in Sponges like Halisarca and Oscarella.

7. Digestive, respiratory, circulatory and nervous systems are absent in Sponges. Digestion of food occurs inside choanocyte cells of the body cavity of Sponges. Respiration occurs by exchange of gases through the general surface of Sponge's body.

8. Food particles along water current enters into the body cavity of Sponges through Oostia. The body cavity of Sponges is known as spongocoel or paragastric cavity. The food particles are digested inside the choanocyte cells which line the inner surface of body cavity and hence the digestion is known as intracellular digestion.

9. Sponges exhibit both asexual and sexual mode of reproduction. Asexual reproduction in Sponges takes place by budding, or fission or by gemmule formation. Fresh water Sponges reproduce by gemmule formation.

10. Sexual reproduction in Sponges occur through gamete formation. All Sponges are hermaphrodite in nature i.e. both male and female reproductive organs are present in the same individual. Sperms and ova are produced in Sponges by archaeocytes. Fertilization is cross and internal in Sponges. Development is indirect with metamorphosis. Amphiblastula and Parenchymula are the two type of larvae found in Sponges.

11. Replacement of injured or lost parts is known as regeneration. Regeneration power is very high in Sponges. A sponge any part of its body is lost accidentally it can regenerate very easily.

12. Most valuable Sponge is 'Turky cup'. The Sponge that is given as gift in Japan is Euplectella. The Sponge that cause harm to pearl industry is 'Cliona'.

A brief study and characteristic features of Phylum Porifera

Introduction

Characteristic features of the animals of Phylum Porifera

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