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Basic Anatomy
Sponges contain no organs or even tissue. Instead, they consist of three cell sized layers. Compressed polygonal cells called pinacocytes make up the pinacoderm, the external sac layer. The cells in the outer layers can move inward and change function. The middle layer is all mesohyl, an extra cellular gelatinous protein/carbohydrate matrix containing mobile amoeboid cells (essentially the invertebrate equivalent of white blood cells), as well as skeletal functions served by spicules or spongin fibers. Although sponges contain no real tissue, the mesohyl serves similar functions as connective tissue, and it is debated whether it and the pinacoderm should be considered tissue. The innermost layer is called the choanoderm, made up of choanocytes, which are flagelled cells.
Sponge pores are called ostia, leading to inhalant canals, which in turn lead to feeding chambers. These chambers are called oscules, made up of choanocytes, whose flagella create a current for the water to flow through.
Sponges contain no organs or even tissue. Instead, they consist of three cell sized layers. Compressed polygonal cells called pinacocytes make up the pinacoderm, the external sac layer. The cells in the outer layers can move inward and change function. The middle layer is all mesohyl, an extra cellular gelatinous protein/carbohydrate matrix containing mobile amoeboid cells (essentially the invertebrate equivalent of white blood cells), as well as skeletal functions served by spicules or spongin fibers. Although sponges contain no real tissue, the mesohyl serves similar functions as connective tissue, and it is debated whether it and the pinacoderm should be considered tissue. The innermost layer is called the choanoderm, made up of choanocytes, which are flagelled cells.
Sponge pores are called ostia, leading to inhalant canals, which in turn lead to feeding chambers. These chambers are called oscules, made up of choanocytes, whose flagella create a current for the water to flow through.