A polypod is an animal of the phylum Polypodia (lit. "many feet"), one of two phyla (body plans) on TIRA 292b. The phylum constitutes animals that have several limbs and are bilaterally symmetrical.
The polypods have a significant amount of diversity, but do have some shared traits:
- A bilaterally symmetrical body plan;
- Six eyes;
- A separate mouth and anus;
- Developed cephalization, with the mouth and central nervous system being located at the anterior of the body
Ancestral polypods had a body comprised of nine-segments, each of which possessed fins and gills. All of the descending lineages have undergone tagmosis of these segments in varying forms.
Aquatic polypods (with the exception of Thalattotheria, which evolved from terrestrial species) have an open-circulatory system with a series of "hearts" appearing at the intersection of each segment, supported by pure muscle. Terrestrial polypods, on the other hand, have developed a closed circulatory system.
Phylogeny EditThe two earliest branches of Polypodia are Tetrabrachia (which includes the planktonic Tachypodia and nektonic Acanthopodia) and the widely diverse Sarcopodia, the latter of which has representatives in virtually every niche of large-bodied animals in TIRA 292b's biosphere. The most notable clade is Osteopoda, which has come to dominate both the terrestrial and pelagic ecosystems.