Top: Demosponge
Middle: Calcareous Sponge Bottom Left: Glass Sponge Bottom Right: Homoscleromorpha |
Sponges make up the entirety of Phylum Porifera. There are close to 9,000 sponge species, divided into four classes.
Demosponges (Demospongiae) The largest class of sponge, including almost 8,000 species, is also the most diverse. They can not be characterized by size, as it is constantly changing. They are characterized, however by their bright colors, which are often associated with sponges. The few freshwater sponges belong to Demospongiae. Calcareous sponges (Calcarea) This class, containing about 500 species, is characterized by spicules, or needle-like structural elements within the sponge, made of calcium carbonate, unlike the silica-based spicules in all other sponges. Calcareous sponges only reach about six inches in height. They usually do not have color, and live near coasts. Glass sponges (Hexactinellida) The third class, also containing about 500 species that appear to be made of glass. That illusion is created by a lattice pattern that forms using number six pointed spicules within the sponge. They live in deep water near the South pole. Homoscleromorpha (Homoscleromorpha) Originally thought to be a part of the demosponges, this group of less than 100 organisms was found recently to be phylogenetically independent. They are characterized by a reduced exoskeleton, and genomic testing has found them to be more closely linked with other animals than the rest of the classes of porifera are. |