Sponges fall into three main groups according to how their bodies are organized. The simplest sponges are the asconoid sponges. These are shaped like a simple tube perforated by pores. The open internal part of the tube is called the spongocoel; it contains the collar cells. There is a single opening to the outside, the osculum. The next-most complicated group is the syconoids. These tend to be larger than asconoids. They also have a tubular body with a single osculum, but their body wall is thicker and the pores that penetrate it are longer, forming a system of simple canals. These canals are lined by collar cells, the flagella of which move water from the outside, into the spongocoel and out the osculum. The third category of body organization is leuconoid. These are the largest and most complex sponges. These sponges are made up of masses of tissue penetrated by numerous canals. Canals lead to numerous small chambers lined with flagellated cells. Water moves through the canals, into these chambers, and out via a central canal and osculum.
Sponges are found in virtually all aquatic habitats, although they are most common and diverse in the marine environments. Many species contain toxic substances, probably to discourage predators. Certain other marine animals take advantage of this characteristic of sponges by placing adult sponges on their bodies, where the sponges attach and grow. The chemicals also probably play a role in competition among sponges and other organisms, as they are released by sponges to insure themselves space in the marine ecosystem. Some of these chemicals have been found to have beneficial pharmaceutical effects for humans, including compounds with respiratory, cardiovascular, gastrointestinal, anti-inflammatory, antitumor, and antibiotic activities. Sponges also provide a home for a number of small marine plants, which live in and around their pore systems. Symbiotic relationships with bacteria and algae have also been reported, in which the sponge provides its symbiont with support and protection and the symbiont provides the sponge with food. Some sponges (boring sponges) excavate the surface of corals and molluscs, sometimes causing significant degradation of reefs and death of the mollusc. The corals or molluscs are not eaten; rather, the sponge is probably seeking protection for itself by sinking into the hard structures it erodes. Even this process has some beneficial effects, however, in that it is an important part of the process by which calcium is recycled.
1-Ascon: the body is composed of a single chamber lined with choanocytes.
2-Sycon: the body is composed of a number of grouped ascon-like
chambers with a central opening.
3-Leucon: the body is composed of a number of sycon-like chambers
which open into the central cavity (paragaster).
No comments:
Post a Comment