Short answers, pulled from the story.
The oldest known kinorhynch Eokinorhynchus rarus lived during the Fortunian stage of the Cambrian period roughly 540 million years ago. This species predates the rise of complex vertebrates by hundreds of millions of years and dates back to the Fortunian of China.
Modern kinorhynch species rarely exceed two millimeters in length while their ancient ancestors were significantly larger. Some Cambrian forms reached lengths that would have been substantial for their time and juveniles begin life with only eight or nine segments.
A kinorhynch body consists of a head neck and trunk divided into eleven distinct segments. These creatures lack external cilia for movement and rely instead on a series of spines that cover their body and form up to seven concentric circles around the head to push forward and grip the substrate.
As of 2022 more than 300 kinorhynch species have been described distributed across 31 genera and 11 families. The genus Echinoderes holds more than 100 species and is the most diverse abundant and commonly encountered of all kinorhynch genera.
Kinorhynchs share a close evolutionary relationship with two other phyla Loricifera and Priapulida. Together these three groups constitute the Scalidophora clade and represent a unique branch of the animal kingdom.