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The Basics of Sponges
The sponges are some of the most primitive multicellular organisms that have been found to date. It is said that these organism would be one of the first multicellular organisms to form on the plant earth due to there lack of complexity yet efficient use of cells division of labor. They are primarily marine organisms however some species may live within freshwater. Zoologists have found roughly 9,000 species of sponges that vary in structure, size, mass, reproduction, and much more.
The Cells, Structure, and Skeleton Associated with the Sponge
- Pinacocytes are thin, flat cells that line the outside of the sponge. They are partially contractile cells that play a major role in the shape of the sponge.
- Porocytes are specialized pinacocytes that mainly regulate water flow and serve as the primary passage for movement of water through the body wall.
- Mesohyl is a jelly like layer located between the pinacocytes that line the outside and the choanocytes that line the inside.
- Mesenchyme (also known as amoeboid cells) are cells located in the mesohyl that specialize in the following:
- Reproduction
- Secreting skeletal elements
- Transporting and storing food
- Formation of contractile rings around openings in the sponge wall
- Choanocytes are specialized flagellated cells that line the inner portion of the sponge. They are primarily used to form a netlike structure that creates a water current throughout the sponge and filters it accordingly.
- Spicules (spongin) are primarily referred to as the skeleton of the sponge. They are formed by amoeboid cells and contain calcium carbonate or silica depending on the species.
Body Types
Reproduction
Sexual Reproduction
Most sponges are monoecious, which means that they produce both sperm and eggs that are needed in fertilization. Although self-fertilization is possible, it is frequently circumvented through different time intervals at which each reproductive gametes is produced. These gametes are produced through choanocytes that undergo meiosis to either form eggs or sperm. The sperm are then released through the osculum to the surrounding environment, which is taken in by incurrent water of other sponges. The sperm is then captured by foreign sponge and placed within a vacuole that is located inside the sponge. The choanocytes that preceded to transport them to the vacuole undergo a chemical change that allows them to become mesenchyme cells, and transport the sperm to the egg. A zygote is finally formed and once developed enough, precedes to break off of the parent sponge and commence its trek to become a full fledged adult.
Asexual Reproduction
To start asexual reproduction gemmules must be produced by the parent sponge, which are composed of a mass of amoeboid cells. These gemmules are extremely hardy and resistant to extreme environmental changes, thus gemmules are usually released from the parent sponge when an environmental change is approaching that will ultimately lead to the parent sponges death. The gemmules hardy nature allows them to survive these harsh conditions and began to organize as a sponge when favorable conditions return.
The Three Major Classes
Calcarea
Composition of Spicules: Calcium Carbonate (CaCO3)
Number of Rays: 3-4 or needle shaped Location: Marine Environment Image from: http://www.cactus-art.biz/schede/TITANOPSIS/Titanopsis_calcarea/Titanopsis_calcarea_bizzare/Titanopsis_calcarea_bizarre.htm |
Hexactinellida
Composition of Spicules: Siliceous
Number of Rays: 6 Location: Marine Environment Image from: http://commons.wikimedia.org/wiki/File:Hexactinellida-uncertain-0126.JPG |
Demospongiae
Composition of Spicules: Siliceous
Number of Rays: 4 or needle shaped Location: Marine and Freshwater Environment Other Important Characteristics: Located in mesohyl of the sponge, brilliantly colored Image from: http://commons.wikimedia.org/wiki/File:Monanchora_unguifera_(Pink_Lumpy_sponge).jpg |