Sponges have only four types of cells:
It is thought that the earliest animal life on Earth resembled sponges. The earliest known multicelled animal fossils are sponges from China that are roughly 600,000,000 years old. Sponges have not been as extensively studied as some other phyla and there may be some suprises still to be found. For example, it has recently been shown that some sponges are not sessile and can move to more favorable locations as rapidly as few cm a day.
Sponges are divided into Demosponges[?], Hexactinellid sponges, and Calcaerous sponges[?] based on the type of spicules in their skeleton. Similar fossil animals known as Chancelloria[?] are no longer regarded as sponges. 90% of modern sponges are demosponges[?]. Demosponges[?] are less common than other sponges, but that is probably because many demosponges[?] have skelatons made only of relatively soft spongin that does not fossilize well. The fossil Archaeocyantha may also belong here, though their skeletons are solid rather than separated into spicules. It has been suggested that the sponges are paraphyletic to the other animals. Otherwise they are sometimes treated as their own subkingdom, the Parazoa.
In common usage, the term sponge is usually applied to the skeletons of these creatures alone, from which the animal matter has been removed by maceration and washing. The material of which these sponges are composed is spongin. Calcareous and siliceous sponges are too harsh for similar use. Commercial sponges are derived from various species and come in many grades, from fine soft "lamb's wool" sponges to the coarse grades used for washing cars. They come from the fisheries in the Mediterranean and West Indies. The manufacture of rubber, plastic and cellulose based synthetic sponges has significantly reduced the commercial sponge fishing industry over recent years.
Sponge is also the name of a Indie rock band; see: Sponge (band)
Search Encyclopedia
|
Featured Article
|