Description

Yohoia is an extinct megacheiran arthropod from the Cambrian period, discovered as fossils in the Burgess Shale formation in British Columbia, Canada. Its type species, Yohoia tenuis, was initially described in 1912 by Walcott, who initially classified it as an anostracan crustacean. Within the Greater Phyllopod bed, 711 specimens of Yohoia have been identified, comprising 1.35% of this community. Fossil specimens of Yohoia range in size from 7 to 23 mm. They feature a head shield, followed by 13 trunk tergites, or plates. Notably, the bottom side of the first 10 plates terminates in backward-pointing, triangular points or projections. The last three plates form complete tubes that encircle the entire trunk. The tail is paddle-like.

Yohoia also displays a pair of prominent extensions at the front of the head shield, each with a noticeable "elbow" and ending in four long spines that resemble fingers. Underneath the head shield, three appendages on each side are believed to have supported the creature while on the sandy or silty sea floor. There are additional single appendages hanging down beneath the body plates. These appendages are flap-like and fringed with setae, likely serving functions related to swimming and respiration. Some bulbous formations at the front of the head shield may have functioned as eyes.

Debate on feeding habits

It is presumed that Yohoia primarily dwelled on the seafloor, swimming just above the muddy ocean bottom and utilizing its appendages to scavenge or capture prey. An interesting feature of Yohoia is a cluster of four large spines at the lower part, which has raised questions about its lifestyle. Some interpretations suggest these spikes were a predatory adaptation, used to grasp smaller creatures for consumption. However, an alternative theory proposes that these spiky appendages were pushed through the soft sediment of the seafloor, filtering and trapping concealed organic matter.

Supporting the notion of Yohoia being a predator is the presence of eyes at the front of the head, indicating forward-facing eyes, a common feature among animals with predatory lifestyles. This arrangement grants improved visual abilities for hunting, such as the ability to judge distances. Nevertheless, the exact interpretation of Yohoia's lifestyle remains uncertain.