Subgroups and Classifications
Small worm-like organisms that crawled along the seabed feeding on detritus and getting additional energy from photosynthesis, these include the oldest members of the superphylum.
The earliest group to branch off, these organisms have a pair of jointed appendages that have been adapted for a wide range of tasks. This group contains the vast majority of faunal species within the whole superphylum.
This particular branch has changed relatively little from their ancestors in overall niche, being small burrowing organisms that primarily live beneath the seafloor. A defining feature of this group is the fleshy parapodia between each of their chitin segments.
Members of this group cling to larger organisms for both food and transportation, either clinging around the waste vent or living within a host's guts. Defining features of this branch include a thinner exoskeleton, the ability to use asexual reproduction, and a suction cup at their rear end used to maintain their grip.
While all the other phyla lost their photosynthetic capabilities, this branch capitalized on that adaptation. Most members of their group have sessile adult stages that rely on photosynthesis for energy, though members of this group have reverted to fauna-like niches on several different occasions.
This monotypic phylum is distinguished from other groups by turning their exoskeleton into a sort of carapace, with a fleshy underside that has hydrostatic legs for locomotion. This branch also possessed a large feeding arm and sharp blade-like projections of their carapace.