Sea sponges are one of the most bizarre living organisms on the planet. They are found in both fresh and sea water and can live at incredible depths eating bacteria and other minerals flowing through the sea. In the past, sea sponges were collected, dried out and sold as sponges for use by humans in bathrooms, although modern sponges are made from synthetic materials.
Sea sponges do not have any kind of mineral skeleton like most animals, but instead use mesohyl, a jellylike substance made up of mainly collagen, sandwiched between two cellular layers to help it keep its structure.
The central structure of the sponge is constrained by two layers of cells which can change into other types of cell depending on what they are needed for. Many of these cells produce collagen to top up the mesohyl, while others produce spermatocytes for reproduction and spicules for help defend the sponge from predators. These nonspecific cells are called archaeocytes.
Sponges do not reproduce sexually or asexually, but instead chart a middle ground which is not dissimilar from plant reproduction. Some sponge cells produce sperm which collect as cysts in the mesohyl. The cells then change to produce eggs which latch onto the sperm deposits. The eggs and sperm combine, spawn, and are excreted by the sponge to grow in another part of the sea.
Feeding, Breathing and Excreting
A water-flow system goes through the middle of the sponge. At one end, essentially the mouth, the sponge collects water and filters out larger particles which cannot pass through it. The smaller food and mineral particles are then ingested, and the remainder of the water is excreted at the opposite end of the sponge.
Nervous and Circulatory System
Sponges have no nervous or circulatory system at all. The changing cells transfer nutrients around the body, and there is no evidence to suggest sponges feel any kind of pain.
Types of Sponge
Although there are hundreds of different species of sponge, some are more common than others. The tube sponge is commonly found on coral reefs around the world. It is made up of several long thin tubes which filter the water. The vase sponge is found around the Caribbean and Florida. This sponge can grow up to 3 feet high and 2 feet wide and looks like a large bowl. Yellow sponges are found in the Pacific and grow in small colonies with each sponge made up of a single small dome. Red tree sponges look more like coral than sponges and are found in the Caribbean Sea.
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