Orthrozanclus reburrus ("Dawn scythe with bristling hair") is a sea creature known from the Middle Cambrian Burgess shale, about one centimeter long, with long spikes protruding from its armored body The describers of this fossil animal, Simon Conway Morris and Jean-Bernard Caron, say Orthrozanclus may have formed a link between the halkieriid and the wiwaxiid families,[1] uniting them tentatively in a group called "Halwaxiida", characterized by a similar type of body armor; these organisms might have been stem group molluscs, or fall as a stem group to the larger lophotrochozoan clade (containing molluscs, annelids and brachiopods). However, the status of the Halwaxiid grouping is not universally accepted.[2] It small but cannot get eaten by Anomalocaris or a another giant predator like Peytoia.

Description Edit

Orthrozanclus reburrus was 6–10.3 millimetres (0.24–0.41 in) long including its long spines, and had a fairly slim, roughly oval body that tapered towards the rear, was distinctly convex on top but was surrounded by a flatter rim. The underside was soft and unarmored, but the upward-facing surfaces were armored by: a small shell, near the front end; three zones of armor plates called "sclerites", which fitted close to the body and one of which ran all the way round the animal; 16 to 20 long, upwards-curving spines on each side of the body. The sclerites and spines were unmineralized, and had internal cavities that appear to have been circular in cross-section. The shell was convex and shaped like a triangle with rounded corners. It had a bulge at the front, a raised rear edge and a ridge along the middle that flared out towards the rear. It also had finely spaced rings that indicate growth by addition of material round the edges, and coarser ridges which may indicate that the animal was metameric, in other words built out of repeated "modules". The function of the shell at the front is unknown.[1] The animal clearly lived on the sea-floor, and is thought to have had a muscular foot rather like that of a snail.[1]