Phylum Mesozoa

Today's animal phylum is a rather obscure one, so obscure that I wasn't able to find a properly licensed image to use. If it helps, here is an image of a member of Class Rhombozoa. 

Mesozoa comes from the Greek for "middle animal" and is a phylum that contains creatures having traits of both protists and flatworms. Though some include this on the list of animal phyla, others do not. This is mainly due to very fuzzy relationships to other animal groups. Studies have shown relationships to both the flat- and roundworms, along with some mesozoans being closer to segmented worms, molluscs, and other invertebrates. Despite similarities, these differences have lead some to split Mesozoa into several phyla based on closest relation. Others maintain their status as a single phylum.

Mesozoans are parasites and show many of the characteristics that are seen in other parasitic creatures. The body form of these animals is very simple, lacking a number of basic systems. They have no nervous system or digestive tract. This simplified body form is likely derived from more complex ancestors, with extra parts being lost when they had become parasitic. Their method of reproduction is quite unusual, with development occurring inside of other cells. No other animal group has shown this sort of method.

Phylum Mesozoa includes two classes: Class Orthonectida and Class Rhombozoa. Orthonectida members can parasitize a variety of invertebrate, marine hosts, while the Rhombozoa members are only found in the kidney-like nephridia of cephalopods.

Source is Biology of the Invertebrates.