Comprehensive Description
Like all sponges they are simple cell aggregates, with multicellular bodies uniquely specialised to filter feeding (Djerassi & Silva 1991). Characteristic dynamic tissues and totipotent (adoptive) cells allow them to change and adopt new positions, and may suggest why they are of the earliest branching metazoans (Degnan et al. 2008). They are sessile, mainly marine acquire food via external pores connected to a flowthrough system of channels and chambers that pump water through. This pumping is usually mediated b y flagellated collar cells known as choanocytes (Degnan et al. 2010). Three forms of porifera occur in ascending order of complexity, characterised by the number of chambers or canals where the waterflow occurs (Ruppert, Fox & Barnes 2004).
Forms of Complexity (composed from information, Hickman et al. 2008)
Compexities in acending order; asconoid, syconoid, lueconoid (Adapted from Hickman et al. 2008; Ruppert, Fox & Barnes 2004)
Demospongiae are silicious, all of the most complex leuconoid design. In this design the choanocytes lie in distinct chambers, compared to being in one large chamber, or canals allowed by the simpler forms. The lueconoid form allows for an increase in complexity and hence an increase in size. The skeleton consists of siliceous spicules that may be bound together by sponging (Hickman et al. 2008).
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