Monday, December 10, 2007

Porifera (Sponges)

kingdom Animalia - animals
Porifera - sponges

Porifera translates to "Pore-bearer". They are the simplest multi cellular animals. They are sessile, mostly marine, water dwelling, filter feeders that pump water through their bodies to filter out particles of food matter. With no true tissues (parazoa), they lack muscles, nerves, and internal organs.

There are three (4?) classes of porifera.

1. Calcarea (calcareous or boney sponges) are the only sponges that possess spicules composed of calcium carbonate. Typically, the Calcarea are very small, measuring about 3-4 inches in height. Of the 15,000 or so species of Porifera that exist, only 400 of those are Calcareans

2. Hexactinellid (glass sponges) are sponges with a skeleton made of four and/or six-pointed silaceous spicules.
Hexactinellids are relatively uncommon and are mostly found at substantial depths.

3. Demosponge:
The Demospongiae are the largest class in the phylum Porifera. Their "skeletons" are made of spicules consisting of fibers of the protein spongin, the mineral silica, or both. They contain 90% of all species of sponges and are predominantly leuconid structural grade.

Subclass Homoscleromorpha
order Homosclerophorida

Subclass Tetractinomorpha
o Astrophorida
o Chondrosida
o Hadromerida
o Lithistida
o Spirophorida

Subclass Ceractinomorpha
o Agelasida
o Dendroceratida
o Dictyoceratida
o Halichondrida
o Halisarcida
o Haplosclerida
o Poecilosclerida
o Verongida
o Verticillitida

4(?). Sclerospongiae (coralline or tropical reef sponges)


Glossary of 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.
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.
Mesohyl (mesenchyme) - the gelatinous layer between the outer body of the sponge and the spongocoel (the inner cavity).
Oscula (pl. osculum) - a large opening in a sponge through which water flows out of the sponge. Sponges may have more than one oscula.
Ostium (pl. ostia) - a pore on the body of a sponge that lets water into the sponge.
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.
Spicule - spicules are sharp spikes 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.

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