Lecture - Phylum Porifera

Types of canal systems in sponges: Asconoid, syconoid, and leuconoid

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Today we discussed the different canal systems in sponges, and how they allow them to  filter water in a more efficient way the more complex the canal system is. In increasing order of complexity such systems are

• Asconoid - the spongocoel is lined with choanocytes
• Syconoid - choanocytes are organized in radial canals and not exposed to the spongocoel
• Leuconoid - choanocytes are organized in interconnected chambers and the individual sponge may have multiple oscula

We also discussed what skeletal elements observed (spicules, collagen fibers, including spongin) and how they are used to classify sponges in three different groups:

• Calcarea - Sponges with calcareous spicules and no spongin (but they do have collagen fibers)
• Hexactinellida - Sponges with six-rayed siliceous spicules and no spongin (they do have collagen fibers)
• Demospongiae - Sponges with spongin and/or siliceous spicules.  Most common of all; they include the carnivorous deep sea sponges (Cladorhizidae, which lack spongin, ostia, and oscula, but have distinctive hooked siliceous spicules)

Representatives of Porifera
from left to right: Sycon quadrangulatum (Calcarea), Xestopongia sp. (Demospongiae),
and Euplectella aspergillum (Hexactinellida)

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