Porifera

Porifera (sponges) are very simple animals found in all parts of the marine environment and especially in coral reefs. They can be many different colours from pale green to bright orange. Some species form a thin layer over stones and dead coral. Others have raised soft and spongy bodies which form lumpy masses or fan-like shapes.

External Features

Any member of some 5,000 species of primitive multicellular aquatic animals that constitute the phylum Porifera. Sponges are characterized by the presence of a porous skeleton of interlocking spicules (bony, needlelike structures), glasslike rods, or horny fibres; they live in colonies or as solitary animals attached to the sea bottom or to other solid objects. Commercial natural sponges are the skeletons that support the sponge animal.

A brief treatment of sponges follows. For full treatment, see Sponges.

All of the 5,000 species of sponge are marine except for about 20 freshwater species ( Spongilla). They occur in all seas, from the intertidal zone to depths of 8,500 m (more than 28,000 feet), and are most common in warm waters. They range in length from a few centimetres to several metres (an inch to several yards). Some rounded forms may be several metres in diameter. The body shape is variable; it may be fingerlike, treelike, or bushy. Some sponges are tubular; others are flat or shapeless masses.

The body of the living sponge is covered by a thin, slimy, usually dark epidermal layer consisting of flat cells called pinacocytes. Numerous perforations lead through the skin into a central cavity, the spongocoel, which is lined with choanocytes--flagellum-bearing cells. These whiplike structures create currents that draw water into the spongocoel through the perforations; the water passes out through one or several large openings, the oscula (singular osculum). Between the outer and inner cell layers is the mesoglea, a jellylike substance containing free-moving cells known as amoebocytes.

The life of a Sponge

The choanocytes ingest food particles--bacteria, other microorganisms, and organic debris--and absorb oxygen from the water current. The amoebocytes produce spherical eggs. After fertilization the larvae swim by means of hairs, or cilia, until they find a suitable site for permanent attachment; they then quickly develop into mature animals. Some species also reproduce by budding, an asexual process in which a section of the adult animal separates and becomes established as a distinct individual.

Reproduction

Sponges reproduce both asexually and sexually.

Asexual reproduction occurs and budding and other processes that produce fragments which develop into new sponges. In fact, sponges have a remarkable ability to regenerate: if a piece is broken off, or a cell suspension is made, the sponge is able to clump, reorganize, attach itself and again become a functional individual.

Both eggs and sperms are produced by the same individual for most species of sexually reproducing sponges. Sperms are carried from one individual to another by water currents. Male and female gametes fuse on contact.