Phylum Porifera

• name means “sponges”
• general characteristics: aquatic, sac like bodies, many pores, sessile (don’t move), filter feeders, multicellular, cellular level of organization, have all 5 types of cell except nerve cell
• 3 layers: outer flatten epidermal cells, middle semi-fluid with wandering amoeboid cells, inner flagellated collar cells
• Choanocytes: flagellated “collar cells” used in feeding
• epidermal cells: the cells forming the outer layer of the animal
• Spicules: rods of silica, spongin (protein) or carbonate that are used for support
• Amoebocytes: amoeba-like cells that transport food, make ‘skeletal’ elements
• Spicules can be made from different materials like Siliceous, Calcareous, and Spongin
• Water flows in through the pore cells into the central cavity and out through the upper opening of the body (osculum)
• Water flow is generated by the beating of the flagella in the chaonocytes
• Feeding process: food particles trapped on collar, food particles transported down the collar, food particles absorbed by cell, food particles transferred to amoebocyte.
• Water movement allows for filter feeding - the pores of the walls and microvilli of the collar cells strain food particles
• Microscopic food particles that pass by the microvilli are engulfed by the collar cells and digested by the collar cells in food vacuoles or passed onto amoeboid cells for digestion
• The only animals where digestion occurs only with cells.
• Amoeboid cells circulate nutrients throughout the sponge (internal transport), produce sex cells, and produce the spicules
• In unfavourable conditions: gemmules are formed (sphere shaped collection of amoebocytes surrounded by a tough layer of spicules), can exist for long periods of time.
• asexual reproduction: fragmentation, budding
• sexual reproduction: release of sperm and eggs in central cavity, zygote develops into a flagellated larvae that can swim to a new location
• Ecological roles: serve as a shelter for other organisms, symbiotic relationships (e.g., photosynthetic symbionts), ”cleans up” the ocean floor, amoebocytes release chemicals that help break down shells and corals, protection: make toxins that discourage animals from chewing on sponges (powerful antibiotics to fight bacteria and some viruses)