One more phylum of meiofauna, microscopic critters living in interstitial spaces! At most a few millimeters but often much smaller, hairybellies are named after the many cilia on their flat ventral surface!
These cilia work in tandem with adhesive tubes - especially on their characteristic forked tail, with which they crawl and slide inbetween sediments to eat, well, the kind of food a tiny guy would eat. Diatoms, bacteria and various kinds of organic matter are on the menu!
As often with these tiny critters, the rest of the body is quite simple - no circulatory or respiratory system, although a roughly differentiated head is visible. The latter often bears sensory cilia - microscopic whiskers! And they have scales covering their back - which is pretty unexpected for an animal that tiny!
Living gastrotrichs are divided in two groups. The chaetonotids have successfully reached both marine and freshwater environments, while macrodasyids stayed mostly marine, but developed two pores on either side of the neck, through which they shoot out water while eating. While extremely commonplace in today's sediments, they unfortunately lack a fossil record, making their relationship with other phyla yet more mysterious!