General Characters and Classification of Sponges

General characters and classification of sponges explains about general characters and classification of sponges.

1. Characters of Sponges

2. Classification of Sponges

Characters of Sponges

General characters of sponges, some of the general characters of sponges are listed below: habitat, body form, symmetry, germ layers, level of organization, body wall, canal system, skeleton, digestioncirculation, respiration, excretion, reproduction, development.

1. Habitat

All sponges are aquatic, mostly marine, rarely fresh water (e.g., Spongilla), solitary or colonial, sessile (attached to the substratum). Sponges like warmer water. They are not usually found in cold water.

2. Body Form

general characters and classification of sponges

Longitudinal section of simple sponge

Their body is porous, viz., provided with pores. The pores are of two types: inhalant pores are called Ostia (sing, ostium) and exhalent pores are known as oscula.

3. Symmetry

Symmetry characteristic of Sponges, most of the sponges are asymmetrical. Some of the sponges radially symmetrical.

4. Germ Layers

The sponges are the first multicellular diploblastic animals, i.e. derived only from two embryonic germ layers, viz., ecto­derm and endoderm.

5. Organization

The sponges have cellular level of organization.

6. Body wall

The body wall of a common sponge consists of three layers.

(a) Pinacoderm: It is outer cellular layer which consists of: (i) Flattened pinacocytes and (ii) Oporocytes.

(b) Choanoderm: It is inner cellular layer which consists of highly specialized flagel­lated cells called choanocytes or collar cells. Both pinacoderm and choanoderm do not have basement membrane.

(c) Mesohyl layer: Basically, it is a non-cellular layer found in between pinacoderm and choanoderm. It has fine dispersed spongin fibres and numerous spicules. It also contains amoebocytes (amoeba-like cells) of both pinacoderm and choanoderm.

7. Canal System

This system consists of pores and canals. Three types of canal systems are found in sponges:

(a) Asconoid canal system: It is the simplest type which is found in Leucosolenia and a few other sponges,

(b) Syconoid canal system: It is more complex than the ascon type. It is found in Sycon and some other sponges,

(c) Leuconoid canal system: It is most complex canal system which is found in Spongilla and some other sponges. In class Demospongiae the leuconoid condition is derived from a larval stage, called the rhagon. The canal system of rhagon larva does not occur in any adult sponge. Because of its derivation from rhagon stage in Demospongiae, the leucon type of canal system is also called the rhagon type.

general characters and classification of sponges

Types of Sponge cells

The central body cavity of a sponge is called spongocoel or Para gastric cavity. The continuous water current flowing through the canal system is very important for the life of a sponge. It brings in food and oxygen and carries away carbon dioxide, excretory matter and reproductive bodies. Thus the canal system helps the sponge in nutrition, respi­ration, excretion and reproduction.

8. Skeleton

Almost all sponges possess an internal skeleton. It may consist of calcareous or siliceous spicules or of fine spongin fibres or of both, located in the mesohyl layer.

9. Digestion

It is intracellular and takes place inside food vacuoles as in protozoans.

10. Circulation

Distribution of food from the ingesting cells to others is brought about by wandering amoebocytes of mesohyl layer.

11. Respiration

Exchange of gases occurs by diffusion through the plasma membranes of the cells as in protozoans.

12. Excretion

Removal of excretory matter also occurs by dif­fusion through the plasma membranes of the cells as in protozoans. Ammonia is chief excretory waste.

13. Reproduction

Both asexual and sexual reproductions occur in sponges. Asexual reproduction occurs by budding and gem mules. In fresh water and a few marine sponges, gem mules or internal buds are formed. Sponges are hermaphrodite. Fertiliza­tion is internal.

14. Development

Zygote undergoes holoblastic cleavage (com­plete division of the zygote). The development includes a free swimming larva, the amphiblastula (in Sycon) or parenchymula (in Leucosolenia) for dispersal of the species.

Classification of Sponge

Sponge kingdom classification chiefly on the basis of skeleton, phylum Porifera (Sponge) is divided into three classes. Class 1. Calcarea, Class 2. Hexactinellida, and Class 3. Demospongiae.

Class 1. Calcarea

The skeleton is of calcareous spicules. Examples: Leucosolenia, Sycon, (Scypha) Grantia.

Leucosolenia: It is a simplest colonial sponge consisting of number of horizontal and vertical tubes. The development is with a larva, the parenchymula. Sycon (Scypha): The development is with a larva, the amphiblastula.

Class 2. Hexactinellida

The skeleton is of siliceous spicules which have six rays. Examples: Euplectella, Hyalonema.

Euplectella:  It is found in deep sea water. They are abundant near the Philippine Island and West Indies. Its skeleton is costly marriage gift in Japan as it is thought to be a symbol of union of wife and husband.

Hyalonema: Hyalonema is fixed in the mud by a root tuft of long, twisted spicules. The upper surface has the gastral cone which bears opening of the ex-current canals. The middle part of the root tuft commonly bears several polyps of symbiotic anemones of the genus Epizoanthus or Polythoa which show symbiotic relation­ship.

Class 3. Demospongiae

The skeleton is of spongin fibres or of spongin fibres with siliceous spicules or may be absent. Examples: Euspongia, Spongilla, Cliona, Chalina.

Euspongia:  The surface is raised into small projections, called the connules. Depressions between the connules bear small pores, the dermal ostea.The oscula are numerous: Its skeleton is used for bathing, washing automobiles, cleaning furniture and window panes. It is used for applying cosmetics, mopping, etc.

Spongilla: Spongilla is a common, widely distributed fresh water sponge shows various shades of green colour because of the symbiotic algae present inside.

Cliona: The sponge can penetrate the rocks and break them into pieces. The sponge can also bore through the oyster shell and, therefore, harmful for pearl oyster industry.

Chalina: The sponge is popu­larly known as “the dead man’s fingers” or “the mermaid’s gloves”, because it is shaped like a hand with several fingers perforated with oscula.

Sponges kingdom some examples

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