Anatomy & Physiology
The body structure of a sponge is divided into three categories; asconoid, syconoid and leuconoid (Hill & Hill 2009). The most commonly found body structure in demospongiae sponges is leuconoid which is a specialised structure to support larger body sizes (Ruppert, Fox & Barnes 2004). The aquiferous system is more complex with more choanocyte chambers and excurrent and incurrent canals (Ruppert, Fox & Barnes 2004). The water flows system is as follow:
ostia → prosopyles → choanocytechambers → apopyle → excurrent → osculum
Drawing of a leuconoid body structure adapted from Ruppert, Fox & Barnes 2004.
Demospongiae sponges body are made up of cells composed into two types of tissues (epithelia and connective) and are arranged into three sections; pinacoderm, mesohyl, choanoderm (Ruppert, Fox & Barnes 2004).
Pinacoderm is the outermost epithelial layer and covers the surface of the body (exopinacoderm) and lines the choanocyte chambers and the excurrent and incurrent canals (Ruppert, Fox & Barnes 2004). It consists of two cells;
1. Platter cell (pinacocyte)
2. Porocyte
Mesohyl in the middle layer made up of connective tissues and contains a majority of the cells in a sponge (Ruppert, Fox & Barnes 2004). The totipotent archeocytes are located in the mesohyl and are capable of differentiating into any other type of sponge cell (Ruppert, Fox & Barnes 2004). Unique to demospongiae are the spongocytes which secrete collagen that polymerises into spogin (Ruppert, Fox & Barnes 2004). There are seven cells located in the mesohyl;
1. Progenitorcells (archeocytes)
2. Crestcells (lophocytes)
3. Hard cells (sclerocytes)
4. Spongocytes
5. Muscle cells (myocytes)
6. Oocytes
7. Spermatocytes
Choanoderm is the innermost epithelial layer and contains the flagellated collar cells (choanocytes) that generate water flow inside the choanocyte chambers (Ruppert, Fox & Barnes 2004).
Drawing of a leuconoid body wall cross section adapted from Ruppert, Fox & Barnes 2004.
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