Chordata
The Chordates are animals that make up the phylum Chordata. The common characteristics of the Chordata include having, for at least some period of their life cycles, a notochord, a hollow dorsal nerve cord, pharyngeal slits, an endostyle, and a post-anal tail.
Ascaris
Ascaris is a genus of parasitic nematode worms known as the "giant intestinal roundworms". One species, A. suum, typically infects pigs. A chordate has an inner skeleton with a backbone. It generally has four appendages that are in the forms of legs, arms, wings or fins. It has muscles in all of it's appendages.
Pristella Maxillaris
The X-ray Tetra or Pristella maxillaris is one of the few chordates with a visible backbone. The spinal cord is housed within its backbone. The X-Ray Tetra is another type of animal in the Chordata phylum. The X-Ray Tetra uses the muscular system because its fins and tail let it swim in the water in which it lives.
Platypus
A Platypus is another type of Chordata. The Platypus uses the muscular system becasue it uses both its tail and its legs to move around and swim. The Platypus also has alot of muscle around his bones and heart which also help him move and do other daily necessities.