pseudocoelomate is an organism with body cavity that is not derived from the MESODERM, as in a true coelom, or body cavity. A pseudocoelomate is also KNOWN as a blastocoelomate, as the body cavity is derived from the blastocoel, or cavity within the embryo. A true coelom is lined with a PERITONEUM which serves to SEPARATE the fluid from the body cavity. In a pseudocoelomate, the body fluids bath the organs, and receive their nutrients and oxygen from the fluid in the cavity.