Phylum II: Porifera (Pore Bearing Animals)
(Latin Porus meaning Pore+fera meaning to bear)
This phylum includes sponges. Their body is perforated by pores.
There are approximately 5,000 species known.
- Multicellular animals, but the cells are not organised into tissues. The presence of collared flagellated cells (choanocytes) is a characteristic feature of sponges.
- Body possesses numerous pores (ostia) which lead into a series of canals. The canals form the canal system through which water flows in and out of the body.
- Sponges have a skeleton which usually consists of calcareous or silicon's silicious or spongin fibres.
- Invariably sessile; body form is vase like, globular or branched: symmetry radial or none.
Leucosolenia, Euspongia (Freshwater sponge), Poterion (Neptunes cup), Sycon, Euplectella (Venus's flower basket), Spongilla (freshwater sponge).
Examples of phylum Porifera: A. Leucosolenia; B. Sycon; C. Poterion; D. Spongilla; E. Euplectella
It is an organic, horny, elastic substance resembling silk in its chemical composition. Tough a protein substance it is resistant to protein-digesting enzymes. The spongin fibres are in the form of fine threads. The fibres are secreted by flask-shaped mesenchyme cells called spongioblasts. Spongin fibres are part of the skeletal structure of sponges.
Economic Importance of Sponges
The ancient Greeks used the dried fibrous skeletons of sponges for washing, bathing, scrubbing the floor and furniture and for padding the shields of armour. Sponges also form food for certain animals. The dried skeletons of a few sponges such as the 'venus flower basket' are used as ornamental articles. Quite a few animals (crustaceans, fishes and molluscs) live in the internal cavities of sponges as commensals or symbionts. The study of sponge regeneration and development help to understand biological facts which help in medical sciences in areas of connective tissue and tissue transplantation.