Marine Phyla Pages -- Coastal Carolina University
PORIFERA
Porifera
____________________
 |
 |
 |
|
www.seashells.org/ images/sponge.jpg |
Defining Characteristics 1
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 asingle 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 flagellae 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.
Systematics 1
Sponges are a diverse group with about 5000 species known across the world. Sponges have cellular-level organization, meaning that their cells are specialized so that different cells perform different functions, but similar cells are not organized into tissues and bodies are a sort of loose aggregation of different kinds of cells. This is the simplest kind of cellular organization found among parazoans.
Reproduction 1
Reproduction by sponges is by both sexual and asexual means. Asexual reproduction is by means of external buds. Some species also form internal buds, called gemmules, which can survive extremely unfavorable conditions that cause the rest of the sponge to die. Sexual reproduction takes place in the mesohyl. Male gametes are released into the water by a sponge and taken into the pore systems of its neighbors in the same way as food items. Spermatozoa are "captured" by collar cells, which then lose their collars and transform into specialized, amoeba-like cells that carry the spermatozoa to the eggs. Some sponges are monoecious; others are dioecious. In most sponges for which developmental patterns are known, the fertilized egg develops into a blastula, which is released into the water (in some species, release takes place right after fertilization; in others, it is delayed and some development takes place within the parent). The larvae may settle directly and transform into adult sponges, or they may be planktonic for a time. Adult sponges are always sessile.
Defense 1
Many species of sponges 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.
Feeding 2
Sponges are characterized by the possession of a feeding system unique among animals. Poriferans don't have mouths; instead, they have tiny pores in their outer walls through which water is drawn. Cells in the sponge walls filter goodies from the water as the water is pumped through the body and out other larger openings. The flow of water through the sponge is unidirectional, driven by the beating of flagella which line the surface of chambers connected by a series of canals. Sponge cells perform a variety of bodily functions and appear to be more independent of each other than are the cells of other animals. Sponges come in an incredible variety of colors and an amazing array of shapes.
Habitat 2
They are predominantly marine, with the notable exception of the family Spongillidae, an extant group of fresh-water demosponges whose fossil record begins in the Cretaceous. Sponges are ubiquitous benthic creatures, found at all latitudes beneath the world's oceans, and from the intertidal to the deep-sea.
Locomotion 2
Generally, they are sessile, though it has been shown that some are able to move slowly (up to 4 mm per day) within aquaria. It is unknown whether this movement is important for sponge ecology under natural conditions. Some sponges bore into the shells of bivalves gastropods, and the colonial skeletons of corals by slowly etching away chips of calcareous material. Another interesting thing can happen when a sponge settles on a snail shell that is being used by a hermit crab; an unusual association (described and studied by Floyd Sandford) can be formed. This sponge/crab association results in a sponge that gets around.
Porifera Links
1. http://animaldiversity.ummz.umich.edu/porifera.html
2. http://www.ucmp.berkeley.edu/porifera/porifera.html