Sarcopodia (lit. "flesh feet") is a branch of Polypodia, notable for its unique form of locomotion and serving as the ancestor of the Osteopods.
The Sarcopods first emerged around 4034ma, beginning as benthic detritivores along the seabed.
Sarcopods have two tagmas: an anterior feeding tagma and a posterior tagma used for locomotion. The tagmosis of the ancestral Polypodia body plan can be summarized as follows:
- Segments 1-3: used for handling food
- Segment 4: used either for digging or for locomotion
- Segment 5: used in increasing respiratory uptake. In Coelopods and Metaxypods, this takes the form of specialized fins on their underside, which beat water over the gill surface to increase oxygen uptake. In the Osteopods, this has evolved into spiracles.
- Segments 6-8: primary locomotive limbs
- Segment 9: Gonopods, used in reproduction
The unique trait of early Sarcopods was their hydraulic locomotion: an offshoot of the haemocoel extends into the limb, with a muscular valve at the base, allowing for the limbs to be inflated and deflated with blood, granting greater support and increased oxygen uptake. This form of locomotion has survived in three of the four lineages of Sarcopodia, and served as the ancestor of the Osteopods' internal skeleton.
- Coelopoda: All modern benthic Sarcopods, largely identical in lifestyle to early Sarcopods.
- Neopoda: Descend from the land-invading Sarcopods, and include the Osteopods.