The sponges (Phylum: Porifera) are relatively simple animals, considered primitive within the animal lineage. They are distinguished by having a body full of pores and channels that circulate a steady stream of water, and hence their name derived from the Latin porus, porous and ferre, to bear. Internally, they are composed of loosely organized clusters of cells that maintain a quasi-independent cellular activity and which have a lack of specialized bodies. Their colors are surprisingly diverse and have widely differing sizes, ranging from a few millimeters to more than 2 m in height.
There are three groups (classes) of sponges, calcareous sponges (Class Calcarea) that have a calcium carbonate skeleton; glass sponges (Class Hexactinellida) that have a skeleton of silica; and demosponges (Class Demospongiae), which are the most numerous, and also have a skeleton of silica, but complemented by a network of organic fibers called “spongin”.
Sponges have colonized all aquatic environments, but they are predominantly marine animals and are found at virtually all depths. Unpolluted coastal areas and tropical reefs are particularly rich in species.
These animals are sessile, i.e. they do not move from one place to another. Although some sponges have a cup-shaped form, most have quite irregular shapes, growing in the form of thin or thick crusts on hard surfaces. Sponges that live in soft substrates tend to be elongated and grow vertically, thus avoiding being covered by sediment.