The First Animals:
Level Of Organization
Sponges have cellular-level organization, meaning that that their cells are specialized so that different cells perform different functions, but similar cells are not organized into tissues and bodies are a sort of loose aggregation of different kinds of cells. This is the simplest kind of cellular organization found among parazoans. There are no distinct tissues or organs.
Only have 1 germ layer
A sponge has either radial symmetry or is asymmetrical.
Sponges do not undergo cephalization because they do not have a brain.
Sponges have a large body cavity that is open to the outside world. It helps them consume food.
Sponges capture food (detritus particles, plankton, bacteria) that is brought close by water currents created by the choanocytes. The water is filtered through pores in the sponge. Food items are taken into individual cells by phagocytosis, and digestion occurs within individual cells.
A sponge has water flow in through the pores. The water contains the food and oxygen the sponge needs.
A sponge takes in water through its pores and in more advanced forms, with canals that move the water to all throughout the sponge. Then the oxygen from the water is used.
A sponge has carbon dioxide and other wastes removed as the water moves in and out through the pores.
A sponge has a very low level reaction to the world around it and does not have a brain or nervous system.
A sponge reproduces by budding and also sexually. Male gametes are released into the water by a sponge and taken into the pore systems of its neighbors in the same way as food items.
Sponges are supported by a skeleton made up of the protein collagen and spicules, which may be calcareous or siliceous, depending on the group of sponges examined
Sources for Info
Sponge Body Cavity and Skeletal System