The First Animal
Level of Organization
Cellular, tissue, or organ/organ-system
Sponges have none, two, or three germ layers
Sponges have radial, bilateral, or even in some cases they don't have any symmetry.
Sponges are not cephalized because they do not have defined head region nor do they have a central location for their nervous system.
The body cavity is a fluid-filled space that separates the gut and internal organs from the rest of the body.
It isolates the internal organs from body-wall movements.
It also bathes the internal organs in a liquid through which nutrients and wastes can diffuse.
There is no segmentation at all in a sponge.
The Digestive System
Sponges are sessile so they cannot pursue their food. Their bodies are covered with pores and canals all over and which water passes. The water moves in and out by the beating of flagella which are parts of choanocytes or collar cells. Cells in the sponges wall capture food that is brought in by the movement of the collar cells. The food is taken in by the process of phagocytosis and each individual cell digests the food.
Sponges have no true circulatory system. But instead, water is circulated by the collar cells, the rate of which can be controlled. Dissolved gases enter and leave cells by diffusion.
A sponge has carbon dioxide and other wastes removed as the water moves in and out through the pores.
A sponge reproduces by budding and also sexually.
A sponge is a hollow tube with many pores or openings. The skeleton is made of lime or silicon