The body of this primitive animal has thousands of pores which let water flow through it continually. Sponges obtain nourishment and oxygen from this flowing water. The flowing water also carries out waste products.

Anatomy: The body of a sponge has two outer layers separated by an acellular (having no cells) gel layer called the mesohyl (also called the mesenchyme). In the gel layer are either spicules (supportive needles made of calcium carbonate) or spongin fibers (a flexible skeletal material made from protein). Sponges have neither tissues nor organs. Different sponges form different shapes, including tubes, fans, cups, cones, blobs, barrels, and crusts. These invertebrates range in size from a few millimeters to 2 meters tall.

Diet: Sponges are filter feeders. Most sponges eat tiny, floating organic particles and plankton that they filter from the water the flows through their body. Food is collected in specialized cells called choanocytes and brought to other cells by amoebocytes.

Reproduction: Most sponges are hermaphrodites (each adult can act as either the female or the male in reproduction). Fertilization is internal in most species; some released sperm randomly float to another sponge with the water current. If a sperm is caught by another sponge's collar cells (choanocytes), fertilization of an egg by the traveling sperm takes place inside the sponge. The resulting tiny larva is released and is free-swimming; it uses tiny cilia (hairs ) to propel itself through the water. The larva eventually settles on the sea floor, becomes sessile and grows into an adult.

Some sponges also reproduce asexually; fragments of their body (buds) are broken off by water currents and carried to another location, where the sponge will grow into a clone of the parent sponge (its DNA is identical to the parent's DNA).

Classification:
Kingdom Animalia (animals)

Phylum Porifera (sponges)

Classes: Calcarea (calcerous sponges - having spicules), Demospongiae (horn sponges, like the bath sponge), Scleropongiae (coralline or tropical reef sponges), and Hexactinellida (glass sponges).

Glossary of Sponge Terms:
archaeocytes (amoebocytes) - Cells with pseudopods, located in the mesohyl. They are used in processing food, distributing it to other cells, and for other functions.
benthic - living at or near the bottom of the seas.
choanocyte - also called collar cells, choanocytes line the inner cavity of the sponge. They have a sticky, funnel-shaped collar (that collects food particles) and a flagellum (which whips around, moving water). The sponge obtains its nutrients and oxygen by processing flowing water using choanocytes. Choanocytes are also involved in sponge reproduction; they catch floating sperm.
epidermis (pinacocyte) - the epidermis is the layer of cells that covers the outer surface of the sponge. The thin, flattened cells of the epidermis are called pinacocytes.
flagellum - the whip-like structure of a choanocyte; the flagellum moves, pushing water (which contains nourishment) through the sponge.
hermaphrodite - an animal in which each adult can act as either the female or the male in reproduction.
holdfast - root-like tendrils that attach the sponge to rocks.
invertebrate - an animal without a backbone.
mesohyl (mesenchyme) - the gelatinous layer between the outer body of the sponge and the spongocoel (the inner cavity).
osculum - a large opening in a sponge through which water flows out of the sponge. Sponges may have more than one oscula.
ostia - a series of tiny pores all over the body of a sponge that let water into the sponge. One of these is called an ostium.
pinacocyte - pinacocytes are the thin, flattened cells of the epidermis, the sponge's outer layer of cells.
porocyte - cells with pores that allow water into the sponge; they are located all over the sponge's body.
sessile - permanently attached to a substrate and unable to move on its own. Adult sponges are sessile.
spicule - spicules are sharp spikes (made of calcium carbonate) located in the mesohyl. Spicules form the "skeleton" of many sponges.
spongin - the flexible, fibrous fibers that form the skeleton of horny sponges; spongin is located within the mesohyl.
spongocoel - the central, open cavity in a sponge through which water flows.
water flows into the sponge - water flows into a sponge through cells with pores (these cells are called porocytes) located all over its body.
water flows out of the sponge - water flows out of a sponge through large openings called oscula (plural). Each of these large openings is called an osculum.

Related Pages:

Sponge Coloring/Information Printout A printable coloring/information page about sponges.

Sponge External Anatomy: Label Me! Printout Label the external anatomy of a sponge and the flow of water through it. Answers

Sponge Internal Anatomy: Label Me! Printout Label the cross-section of a sponge and the flow of water through it. Answers

Invertebrates Invertebrates are animals that lack a backbone.

Coral Reef Animals Coral reefs are warm, clear, shallow ocean habitats that are rich in life.

Ocean Animals The seas and oceans of the world are teeming with life.

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