Phylum Porifera
Phylum Porifera, commonly referred to as sponges, includes simple aquatic animals that are primarily marine. They are known for their cellular level of organization, where cells are loosely aggregated rather than organized into tissues or organs. Most sponges exhibit asymmetry, although some may have radial symmetry.
Key Features:
- Water Transport System: Water enters the sponge through small pores known as ostia, flows into a central cavity called spongocoel, and exits through a larger opening called the osculum. This water flow aids in nutrition (filter feeding), respiration, and waste removal.
- Choanocytes: These specialized cells line the spongocoel and are equipped with flagella that create a water current for feeding and respiration.
- Skeletal Structure: Sponges have a supportive skeleton composed of spicules (tiny, needle-like structures) or spongin fibers, contributing to their strength and flexibility.
- Reproductive Strategies: Sponges are hermaphrodites; they can produce both eggs and sperm. Fertilization occurs internally, followed by the development of a morphologically distinct larval stage.
Examples:
Common examples include Sycon (Scypha), Euspongia (bath sponge), and Spongilla (freshwater sponge).
The study of Porifera is significant in understanding the evolutionary biology of animals, as they represent one of the earliest branches of multicellular life.