| Mosura fentoni | |
|---|---|
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| Holotype of and fourMosura referred specimens | |
Scientific classification | |
| Kingdom: | Animalia |
| Stem group: | Arthropoda |
| Class: | †Dinocaridida |
| Order: | †Radiodonta |
| Family: | †Hurdiidae |
| Genus: | †Mosura Moysiuk & Caron,2025 |
| Species: | †M. fentoni |
| Binomial name | |
| †Mosura fentoni Moysiuk & Caron, 2025 | |
Mosura fentoni (IPA:[ˈmɒsuɾɑ]) is an extinct species ofhurdiidradiodont from theCambrianBurgess Shale inBritish Columbia, Canada.M. fentoni is theonly species in the genusMosura, and is known from sixty specimens collected between 1990 and 2022.
Mosura fentoni is known from sixty specimens. Theholotype, ROMIP 67995 preserves a complete individual in dorsal view. Other notable specimens are ROMIP 66108, ROMIP 67998, ROMIP 68004, ROMIP 67999, and ROMIP 67979, which all preserve internal organs. The specimens were discovered in the Raymond Quarry andMarble Canyon localities within theBurgess Shale from 1990 to 2022, with the majority being placed in the invertebrate paleontology collection of theRoyal Ontario Museum (ROMIP).[1]
In 2025, Moysiuk & CarondescribedMosura fentoni as a new genus and species of radiodont based on these fossil remains. Thegeneric name,Mosura (IPA:[ˈmɒsuɾɑ]), is named afterMothra (モスラ,Mosura) a moth-likekaiju monster featured in films by the Japanese companyToho. The name was chosen forM. fentoni in reference to the animal's moth-like appearance. The name was romanized according toHepburn style. Thespecific name,fentoni (IPA:[ˈfɛntənaɪ]), honours Peter E. Fenton and his work as a technician in the Royal Ontario Museum Invertebrate Palaeontology section, and for his unwavering friendship to both authors.[1]
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Mosura is known from specimens ranging in length from 1.5 to 6.1 centimetres (0.59 to 2.40 in), making this taxon one of the smallest radiodonts known. The head has three eyes: a pair of eyes on short stalks and amedian (midline of the head) eye. The body is divided into 26 segments, the highest number found in any radiodont. The primary body sections are the head, the four-segmented neck, and the trunk. The trunk is divided into theanterior (toward the front) six-segmented mesotrunk, andposterior (toward the back) posterotrunk, which has at most 16 segments. Like other radiodonts, the body bears pairs of swimming flaps, which are considerably larger on the mesotrunk than on the posterotrunk. The gills are very large compared to body size.[1]
Mosura is one of four radiodont taxa with known juvenile fossils (the other three beingLyrarapax unguispinus,[2]Amplectobelua symbrachiata,[3] andStanleycaris hirpex[4]). The juveniles inMosura are distinguished by fewer segments in the posterotrunk, and possibly mesotrunk. An increase in total segment number during ontogeny (hemianamorphosis) is consistent with previous observations inStanleycaris.[4] Moysiuk and Caron (2025) noted that an increase in mesotrunk segment number implies that some posterotrunk segments would have differentiated during ontogeny, incorporating with the mesotrunk. They note that this is uncommon, but not unprecedented, as this has been observed in otherarthropod groups, such as thefuxianhuiidFuxianhuia.[1][5]
Mosura has a mixture of traits known from otherbasal hurdiids and non-hurdiids (elongate and multisegmented body, short head, distinct and constricted neck region, and small roundedH-element), traitsapomorphic to Hurdiidae (single row of six elongate and mesially/toward the body midline curvingendites on the frontal appendages), traits shared by other hurdiids (inner plates in theoral cone, tetraradial arrangement of the oral plates, absence of posteriorauxiliary spines on the frontal appendage endites), andderived traits (median eye, specialised respiratorytagma). It is not known whether the median eye in this taxon wascompound or if it had a single lens, however Moysiuk and Caron (2025) favor the single lens theory, pointing to similarities between it, and the potentially homologous median eyes seen incrown-group euarthropods. Similar toStanleycaris, this taxon seemingly lacks lateral sclerites (formally known asP-elements), a trait only seen within hurdiidae between the two genera.[1][6]
In theirphylogenetic analysis, Moysiuk and Caron (2025) recoveredMosura as a basal (early-diverging)radiodont in the familyHurdiidae, finding it to besister to all other hurdiids. Radiodonts are a diverse and long-lasting order of lowerPaleozoic marinepanarthropods. The results reproduced in thecladogram below are based on their prunedmaximum clade credibility tree, they also produced a majority rule consensus tree whereMosura was found to be in apolytomy withStanleycaris,Schinderhannes,Peytoia and the clade formed byAegirocassis and Hurdiinae.[1]
Mosura is one of three basal hurdiidgenera that show a mixture of traits expected from hurdiids and non-hurdiids, the others beingStanleycaris (the only other radiodont taxon currently known with a median eye[6]) andSchinderhannes.[7] Regarding the specialised respiratory tagma, the authors speculate that they were—in conjunction with the reduced size—an adaptation for the oxygen-stressed environments that were proximal to the site of burial. However, while they find it unlikely, they could have been an adaptation to distinct behavioural traits such as the proposed nektobenthic sediment-sifting macropredatory ecology proposed for most hurdiids.[1]
Mosura is interpreted as an actively swimming (nektonic) predator of prey relatively large compared to its body size. Its large gills despite its small body size suggests it may have inhabited low oxygen environments such as theouter continental shelf. This taxon was most likely a highly maneuverable swimmer, with Moysiuk and Caron (2025) suggesting the median eye in this hurdiid functioned similarly to those seen in modernodonates (specificallydragonflies), and would have helped the radiodont maintain its orientation when chasing fast moving prey.[1][8]
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