''Myxinikela'' is an extinct genus of

stem Stem or STEM most commonly refers to: * Plant stem, a structural axis of a vascular plant * Stem group * Science, technology, engineering, and mathematics Stem or STEM can also refer to: Language and writing * Word stem, part of a word respon ...

hagfish Hagfish, of the Class (biology), class Myxini (also known as Hyperotreti) and Order (biology), order Myxiniformes , are eel-shaped Agnatha, jawless fish (occasionally called slime eels). Hagfish are the only known living Animal, animals that h ...

known from the

Late Carboniferous Late or LATE may refer to: Everyday usage * Tardy, or late, not being on time * Late (or the late) may refer to a person who is dead Music * Late (The 77s album), ''Late'' (The 77s album), 2000 * Late (Alvin Batiste album), 1993 * Late!, a pseudo ...

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

, USA. It is the earliest definitive hagfish known from fossil remains, and one of only two alongside the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

crown-group In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...

hagfish '' Tethymyxine''. ''Myxinikela'''s anatomy displays basal features of cyclostomes (cartilaginous branchial baskets, separation between esophageal and branchial passages, and a well-differentiated midline finfold), giving it a somewhat

lamprey Lampreys (sometimes inaccurately called lamprey eels) are a group of Agnatha, jawless fish comprising the order (biology), order Petromyzontiformes , sole order in the Class (biology), class Petromyzontida. The adult lamprey is characterize ...

-like appearance, but it also has numerous derived traits of hagfishes such as a nasohypophyseal aperture, large velar cavity, and a cardinal heart; due to this, ''Myxinikela'' can be considered a transitional form between basal cyclostomes and modern hagfishes. ''Myxinikela'' is known from two specimens from the Mazon Creek fossil beds; such fossilized cyclostome specimens are rare due to their soft bodies, requiring very specific methods of preservation. ''Myxinikela'' fossils are known from Francis Creek Shale, fossil layers which are thought to represent a shallow-water environment of fluctuating salinity and turbidity; this contrasts with modern hagfishes, which inhabit deep-water environments. As ''Myxinikela'' fossils are rare in the well-studied formation, this indicates it was likely either an overall rare species, a seasonal migrant through the area, or that the fossils represented transient members from nearby habitats.

References

{{Taxonbar, from=Q20859372 † Carboniferous jawless fish Carboniferous Illinois Paleontology in Illinois Pennsylvanian fish of North America Fossil taxa described in 1991