General Information

Sea Sponges a.k.a. Poriferans, are the simplest of animals. They don't have any real tissues, nerves, muscles, or internal organs. There are currently 5,000 known speices of Poriferans. They are also generally asymmetrical in body shape, sessile, and marine dwelling. They generally live in the intertidal zone, which at low tide is exposed to the air and at high tide is submerged underwater. However, some sponges may live at depths as deep as 8,500m. The sponge creates hard structures within itself called Spicules form the skeleton. Other sponges use Spongin instead of Spicules, spongin is stronger and softer than spicules.

DID YOU KNOW? They can grow to be 4 feet long that is the biggest sponge ever recorded.

Basic Structure

The sponges have a simple body plan. Its body, the central cavity is surrounded by a wall that has thousands of openings, or pores. A current of water that enters these pores are powered by the flagella of cells called collar cells. The water exits through a large hole called osculum.

The skeletal system of the sponges are composed of spicules. These spicules are made of calcium carbonate and are secreted by special cells called amoebocytes.

Other kinds of sponges have skeletal system made of spongin. Cells of the body grow around these fibers and are thus supported by the protein matrix.

For commercial harvest, the sponges are dried and washed to remove the cells and the protein meshwork. Then, they are sold as natural sponges for bathing or washing cars.

Deep ocean sponges, called glass sponges, have elaborate skeletons made from silica that support the cells of the body. The elaborate structure of glass sponges are shown below. For a detailed explanation, go to http://www.promotega.org/ksu00019/glass_sponges.htm

Habitat and Adaptations

Sponges spend their lives anchored to a solid surface underwater. Most sponges are marine, although some live in fresh water. Sponges can be found on ocean floors in most places around the world. Most of them live along the coast in shallow water. But, some sponges, such as the fragile glass sponge, are found very deep in the ocean, where water currents are slow and do not disturb them.

As marine environments grow, sponges find that they have more competition around them. Therefore, sponges will emit toxic substances into the water to scare off other organisms, to ensure a place to grow. In some cases, sponges do not frighten off other marine animals. They will be involved in symbiotic relationships with bacteria and algae where the sponge provides support and protection and the symbionts provide food for the sponge.

DID YOU KNOW? If the sponge breaks a peace or damages it the sponge will grow back the part of there body that broke off this is called regeneration.

Feeding & Respiration

Sponges are filter feeders. This means that water flows through the porous body of sponge, and any food/nutrient will get filtered out from the water. The food particles, such as tiny plants or animals will be absorbed into the central cavity. As the water moves through the sponge, food particles stick to the collar cells. The trapped particles are then engulfed by the collar cells or they are passed on to the amebocytes.

Sponges have no respiratory or excretory glands/organs. All of these processes occur through diffusion within individual cells. The water also serves as sponges' respiratory system. As water passes through the body cell, sponge cells remove oxygen and give off carbon dioxide into the water. The wastes that are produced by cellular respiration are also released into the water. The water then carries the wastes away.

Sponges have flagellated cells called choanocytes which line the interior. The flagellum are surrounded by microvilli, and the movement of the flagella (of the Collar Cells) pump water through the body of the sponge. The collar of the choanocyte is also where most of the diffusion of nutrients into the sponge takes place.

Digestion

Archaeocytes are amoeboid and can change into all other types of sponge cells. In addition, they also ingest and digest food which are caught by the choanocytes. They transport the nutrients to other sponge cells. Tiny food particles stick to the collar cell, where they may be digested. If the collar cell doesn't digest the food, they pass it on to the amebocytes. When food particles are digested, amebocytes deliver digested food to other parts of the sponge. Digestion of sponges is intracellular, takig place inside cells.

Circulatory System / Excretion

Sponges do not have a true circulatory system, however, flowing water is used instead. Gasses are brought to the cells by the current and enters the cells through diffusion. Archaeocytes deliver the nutrients. Sponges do not have any excretory organs and excretion occurs on the cellular level with each individual cell diffusing their wastes into the water. The water that flows in through the pores of the sponge exit through the Osculum.

DID YOU KNOW? There are sponge fossils that actually date back to one billion years ago.

Reproduction

Sponges are capable of reproducing sexually and asexually. Sponges reproduce asexually by Budding; when the mature sponge grows a new sponge off of itself, and the sponge pops off when it matures. The offspring sponge has exactly the same genetic material as the parent. In sexual reproduction, sponges create eggs and sperms which fertilize those of other sponges. Although sponges are hermaphrodites, they do not fertilize their own eggs with their own sperm (this would be asexual reproduction). All sponges in an area generally release their eggs and sperm on the same night, producing new sponges with different DNA. The zygote can swim and get carried by the current for long distances before settling down and becoming a new sponge. Some sponges also form Gemmules which are structures which hold amoebocytes (aka Archaeocytes) within a thick shell of spicules. These can withstand harsh winters which would kill adult sponges. When favourable conditions return, gemmules grow into sponges again.