Demosponge

Demospongiae is a class of freshwater and marine sponges that belongs to the phylum Porifera. More than 90% of the 5,000 species of sponges are demosponges, making this class of sponge by far the biggest. These sponges are soft but tough and brightly colored, coming in different shapes, sizes, and textures, this group is the most varied class.

Body Design
Most demosponges are shaped like a rock. While one end will be attached to a stone or hard surface, the other end of the sponge will be open to the water, thus making the demosponge's body type a leuconoid. Leuconoid is the most complex body form of a sponge, it is irregular, asymmetrical and has secondary folds. Tiny pores in the spongocoel (inside of the sponge) allow water to enter in place of the mouth that they lack. Demosponges come in sizes ranging from two millimeters to over two meters. The demosponge's skeleton consists of spongin fibers or siliceous spicules and in some cases both. Spongin fibers are a scleroprotein that forms the skeleton of some sponges. Unlike the sponges of the Hexactinellida class, demonsponges do not have six-rayed spicules, they instead have one to four-rayed spicules that have axial canals throughout the sponges body ,though one genus (Oscarella) has no skeleton at all. Demosponges can vary in shape, they can be reticulate, confused, radial, plumose or axially compressed.

Life Cycle
Sexual Reproduction

Demosponges have male and female reproductive systems, as well as the ability to reproduce sexually or asexually. Some demosponges release their eggs and sperm into the water where they are fertilized and when they hatch, the larvae float until they attach themselves onto a stable surface. Only a few sponges reproduce this way. Most sponges are viviparous, keeping their eggs inside fertilizing the eggs internally. When the sperm is released it floats until it reaches another sponge of the same species. Once the eggs hatch the larvae swim out of the spicules and into the water where they will float freely until they reach a solid ground to attach themselves to. After the larva attaches itself to a stable surface, most adult sponges will remain sessile for the rest of their lives though very few may move at times. Average life span of a demosponge is 5-30 years.

Asexual Reproduction

One form of asexual reproduction happens when a adult sponge is faced with a hostile environment and it forms gemmules (internal bud) that are resistant to harsh conditions and when those conditions cease a new sponge grows from that gemmule. Another form of asexual reproduction takes places after an external bud becomes to big and breaks off, this results in a mini "clone" of the adult sponge.

Ecology
Habitat

Most demosponges occur in all depths in the water and can be found world wide, while some orders of this class are confined to certain areas. Classes Astrophorida, Chondrosida, Hadromerida, Halichondrida, Haplosclerida, Homoscleromorpha, Poecilosclerida and most Spirophorida are found in all regions while Agelasida, Dictyoceratida, and sclerosponges are mostly in the tropics. Other classes like Verticillitida, Spirasigmidae, Pseudoceratinidae and Aplysinellidae, are only encountered in the Pacific and Indian Oceans. Either way sponges need to be in the water to survive because they can not receive the oxygen or food they need without it.

Feeding

Most demosponges filter water through their spicules to pick up tiny particles of food from the water. This is what classifies them as filter-feeders. But Chondrocladia is a genus of deep-sea sponge in the order Poecilosclerida and is unlike other sponges, which obtain food by filter-feeding. Chondrocladia sponges eat small shrimp and other crustaceans that stick to the sponge's translucent globes, thus making them carnivorous by nature.

Importance
Demosponges are of economic value to humans because they can be harvested and grown commercially as bath sponges. Scientists think that sponges may hold the key to helping cure cancer and other diseases because of their ability to clean, filter, and eat substances that are put into the water. It is also important to know that while there may be good benefits to these animals there is also a down side, some species release a toxic substance when competing for space against other animals, thus polluting our waters.