Porifera (general)

• Porifera are sea sponges
• They are the most primitive of multicellular animals
• No organs or organised tissues
• Cells perform various functions
• Always sessile (fixed in one place) but some can move.
• rely on maintaining constant water flow to obtain oxygen, food and remove waste
• 5000 marine species
• mainly in shallow water, one group in deep sea
• variable in shape and size, often brightly coloured
• they have mesophyl (connective tissue) sandwiched between 2 main layers of cells
• Choanocytes are flagellated cells which line the internal chambers of sponges (used for filter feeding)

  
• Spicules are structural elements found in most sponges, they can be calcareous or siliceous.

  Megascleres are large spicules

  Microscleres are small spicules
• they can reproduce asexually or sexually and fertilisation can be internal or external
• an example of external fertilisation is when sequential hermaphrodites release gametes into the water
• some are viviparous, choanocytes of adjacent individuals recognise or capture sperm without digesting them and transfer them to oocytes (an immature egg cell)

  
• They can bore into rocks or encrust (cover) on substratum (underlying surface/base on which an organism attaches).
• They have different morphology including:

  Asconoid -> simplest body structure, water enters through pores called Ostia.

  Syconoia -> similar to, but wall is more pleated, so more choanocytes.

  Leuconoid -> network of these chambers, so even more choanocytes.
• Archeocytes: large, phagocytic, used in digestion, cantransform into other cell types, can produce eggs but notsperm.

  Collencytes: secrete collagen.

  Sclereocytes: secrete spicules.

  Spongocytes: secrete spongin (thick fibrous material whichstiffens mesophyll).

  Choanocytes: flagellated cells that create currents of waterin the sponge, produces sperm and can produce eggs.
• Their feeding is basic but efficient.

  They feed on very fine plankton including bacteria and dino-flagellates

  The specialised, flagellated cells are called choanocytes and these move flagella to draw in water through pores.

  They don't have a gut, so there is direct ingestion of captured food.