Phylum : Arthropoda
Class : Megacheira
Family : Yohoiidae
Genus : Yohoia
Species : T. tenuis
Burgess shale, Canada (map)
Yohoia is a tiny, extinct animal from the Cambrian period that has been found as fossils in the Burgess Shale formation of British Columbia, Canada. It has been placed among the arachnomorphs, a group of arthropods that includes the chelicerates and trilobites. Their sizes range from 7 to 23 mm. 711 specimens of Yohoia are known from the Greater Phyllopod bed, where they comprise 1.35% of the community.
Specimens of Yohoia have a head shield which is followed by 13 trunk tergites, or plates. On both sides, the bottom side of the first 10 of these ended in backward-pointing, triangular points or projections. The last three plates were complete tubes, circling the entire trunk. At the end of the trunk was a paddle-like tail. There were also a pair of large extensions at the front of the head shield. They had a pronounced "elbow" and ended in four long spines, looking rather like fingers. There were three appendages on the bottom of the head shield on each side, and these are assumed to have supported the creature on the sandy or silty sea bottom. There were also single appendages hanging down under the body plates which were flap-like and fringed with setae, probably used for swimming and respiration. Specimens also show some bulbous formations at the front of the head shield that may have served as eyes.
Yohoia is assumed to been a mainly benthic (bottom-dwelling) creature that swam just above the muddy ocean floor and using its appendages to scavenge or capture prey.
