Animals - Phylum Porifera

Porifera = Sponges

  • General Characteristics of Sponges (Porifera):

    • Aquatic, multicellular organisms with a sac-like body.

    • Sessile (non-motile) filter feeders.

    • Cellular level of organization.

    • Lack nerve cells.

  • Sponge Structure:

    • Three layers: outer epidermal cells, middle semi-fluid with amoeboid cells, and inner flagellated collar cells (choanocytes).

    • Many pores ("porifera").

  • Cell Types:

    • Choanocytes: Flagellated collar cells for feeding; generate water flow.

    • Epidermal cells: Form the outer layer.

    • Spicules: Rods of silica, spongin (protein), or carbonate for support.

    • Amoebocytes: Transport food and make skeletal elements.

  • Support:

    • Spicules are embedded in the mesohyl.

    • Spicule composition: siliceous (Silica) →SO2; Calcareous (Calcium) →CaCO3, Spongin (protein)

    • Branches needles of calcium carbonate or silica which support the body

    • Spicule arrangement: haphazard or precise, used for classification.

  • Water Flow and Feeding:

    • Water enters through pore cells into the central cavity and exits through the osculum.

    • Water flow generated by the beating of flagella in choanocytes.

  • Feeding Mechanism:

    • Filter feeding: food particles strained by pores and microvilli of collar cells.

    • Food particles are engulfed by collar cells and digested in food vacuoles or transferred to amoeboid cells.

    • Digestion occurs only within cells.

  • Amoeboid Cells Function:

    • Circulate nutrients.

    • Produce sex cells and spicules.

  • Reproduction:

    • Asexual: fragmentation and budding.

    • Sexual: release of eggs and sperm into the central cavity; zygote develops into flagellated larvae.

  • Gemmules:

    • Sphere-shaped collections of amebocytes surrounded by spicules, allowing survival in unfavorable conditions.

  • Ecological Role:

    • Shelter for other organisms.

    • Symbiotic relationships (e.g., photosynthetic symbionts).

    • Cleaning up the ocean floor by breaking down shells and corals via chemicals released by amebocytes.

    • Protection through toxins that discourage predation; these chemicals can act as antibiotics.