Mosura

A colored line drawing of the extinct marine invertebrate Mosura. It has a squarish head with a pair of large round compound eyes and a third oval eye in the middle of its face, almost looking like a "nose". A pair of spiny grasping claw-like appendages extend from the underside of its head. It has a long segmented body lined with pairs of triangular swimming flaps, with six larger pairs in the middle of its length and much smaller flaps along its narrower "tail"-like region. It's depicted colored green, with red eyes and red and blue markings.

Mosura fentoni was a small radiodont living during the mid-Cambrian, about 508 million years ago, in near-equatorial shallow marine waters covering what is now western Canada.

Sixty specimens have been discovered in the Burgess Shale fossil deposits, ranging from 1.5cm long juveniles (~0.6″) to 6cm long adults (~2.4″), giving us a detailed look at Mosura’s anatomy and life history. It had three eyes – two on the sides of its head on short stalks and one in the middle of its face – and a pair of grasping frontal appendages each with six long sickle-shaped spines.

Unusually for a radiodont its body was divided into distinct regions: a four-segment neck, a six-segment mesotrunk with large swimming flaps, and an abdomen-like posterotrunk with up to at least sixteen segments (fewer in juveniles), all bearing gills along their undersides.

Its vaguely moth-like shape led to it being nicknamed “sea-moth” by field collectors, and inspired its genus name – “Mosura” is the Japanese name of the fictional giant kaiju moth-monster Mothra.

With a very high proportion of respiratory surface area for its size, Mosura was probably an active and agile fast-swimming predator, possibly living in low-oxygen waters around the outer continental shelf. Its wide oval central eye may have helped it stay orientated during rapid maneuvers, keeping track of the horizon line similar to the median eyes of modern dragonflies.

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