What term describes a triploblastic animal with a body cavity partially lined with mesoderm?

In developmental biology, a triploblastic animal is characterized by having three germ layers: ectoderm, mesoderm, and endoderm. The term that accurately describes a triploblastic organism with a body cavity that is only partially lined by mesoderm is "pseudocoelomate."

Pseudocoelomates possess a body cavity known as a pseudocoel, which is derived from the blastocoel of the embryo and is located between the endoderm and mesoderm. This cavity is not completely surrounded by mesodermal tissue, differing from true coelomates, where the body cavity is fully lined by mesoderm. The presence of this type of body cavity allows for greater flexibility and movement of internal organs, and is a characteristic feature of many animal phyla, such as Nematoda (roundworms).

In contrast, deuterostomes and protostomes refer to classifications based on the developmental fate of the blastopore and other embryonic development characteristics, not specifically regarding the structure of the body cavity. An acoelomate, on the other hand, describes an organism that lacks a body cavity entirely, which does not fit the criteria outlined in the question