![]() ![]() Groups of cells in the nerve net form nerve cords that may be essential for more rapid transmission. The function of the nerve cells is to carry signals from sensory cells and to contractile cells. The nervous system is primitive, with nerve cells scattered across the body in a network. However, organs and organ systems are not present in this phylum. There are differentiated cell types in each tissue layer, such as nerve cells, enzyme-secreting cells, and nutrient-absorbing cells, as well as intercellular connections between the cells. Between these two layers is a non-living, jelly-like mesoglea. The outer layer is called the epidermis, whereas the inner layer is called the gastrodermis and lines the digestive cavity. All cnidarians have two tissue layers, with a jelly-like mesoglea between them.Īll cnidarians have two tissue layers. Contractile myocyte cells are present around osculum, a large pore for throwing out water from spongocoel.\): Cnidarians have two distinct body plans, the (a) medusa and the (b) polyp. Then there are spongocytes which secrete skeletal material. Ectodermal or outer layer of sponge body is made up of pinacocyte cells. There are several other cells in Porifera. The pore through which water flows in is called ostium (singular). Each porocyte allows water to flow inside the spongocoel from surrounding aquatic habitat. Porocytes are unique, elongated, tubular cells. Digestion is also intracellular, taking place within choanocyte. These cells capture microcopic food particles. Choanocyte also has a collar made of microvilli. ![]() As mentioned above, sponges are diploblasts and consist of essentially two cell layers. They obtain oxygen by diffusion from the water flowing through their bodies, and waste is expelled by diffusion into the same pool of water. The flagella help in creating a unidirectional flow of water around the body of sponge. Since sponges do not have organ systems they do not posses a respiratory or circulatory system. Moreover choanocytes also give rise to germ cells.Ĭhoanocytes are flagellated cells which line the spongocoel and form the so called 'choanoderm': the layer represents endoderm of a diploblastic poriferan organism. Archaeocytes are totipotent cells which can differentiate into other cell types within the body of sponge. ![]()
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