Scientists have discovered a half a million years old three eyed “sea moth” from a cache of museum fossils in Canada. These finger-sized feisty predators are speculated to lurk in the primordial seas, hooking prey into its mouth while breathing through long gills on its butt. This species is named Mosura fentoni because of its resemblance to the fictional Japanese monster Mothra. This species, belonging to the group of ancestral arthropods called radiodonts, gives valuable insight towards the surprising diversity and adaptations in the ancient arthropods.

About the species

According to a study by Paleontologists Joseph Moysiuk and Jean-Bernard Caron, earliest-diverging arthropods, the radiodonts, exhibited comparatively limited variability in tagmosis. Unlike them, the newly found species M. fentoni exhibits up to 26 trunk segments, the highest number reported for any radiodont, despite being among the smallest known.

The species also had the longest gills relative to body length of all known radiodonts. the back-end gills were most likely a specialized system for respiration; horseshoe crabs, wood lice and some other living arthropods have subsequently evolved a similar system. Researchers aren’t certain why M. fentoni needed the long butt gills, but they speculated it was an adaptation to low-oxygen environments or an active lifestyle.

While paleontologists are still learning why Mosura fentoni had a third eye, researchers believe the eye may have been used to detect light and the seascape it moved through. Perhaps Mosura fentoni’s median eye was used to orient themselves during high-speed hunts, according to the U.K. Natural History Museum.

Key Insights

Arthropods are a large group of invertebrates with hard exoskeletons, segmented bodies and jointed legs. Today, they make up around three-quarters of all living animals, including insects, arachnids and crustaceans. One of the reasons for their evolutionary success is their specialized body segments. Radiodonts are probably the first group of arthropods to branch out in the evolutionary tree, so they provide key insight into ancestral traits for the entire group. The new species emphasizes that these early arthropods were already surprisingly diverse and were adapting in a comparable way to their distant modern relatives.