A Paleozoic stem hagfish Myxinikela siroka—revised anatomy and implications for evolution of the living jawless vertebrate lineages

Myxinikela siroka holotype FMNH PF15373 and paratype FMNH PF8472 from the Moscovian Francis Creek Shale, approximately 310–307 Ma, preserve a cyclostome–hagfish anatomical mosaic and support a stem or putative total-group hagfish interpretation; they do not set the crown-Myxini range or demonstrate modern hagfish habitat, slime production or ecology.

Myxinikela siroka is represented by holotype FMNH PF15373 and paratype FMNH PF8472 and is interpreted as a stem or putative total-group hagfish, not a crown-Myxini member.

Both represented Myxinikela specimens come from the Moscovian Francis Creek Shale at the former Pit 11 locality in Illinois; no broader distribution is inferred.

The fossils preserve body outlines and soft-tissue traces but do not directly establish diet, slime production, habitat preference or feeding guild.

The two specimens preserve a cyclostome–hagfish anatomical mosaic, with body lengths of 73.3 and 62.5 mm and multiple structures whose interpretation depends on preservation.

The displayed 310–307 Ma interval bounds the represented Francis Creek Shale specimens and is not the duration or global first appearance of hagfishes.

The Cyclostome fossil evidence route navigation entity is source-linked only to the named specimen, dataset and analysis dossiers already cited by its range ledger. Its displayed span is a study-bounded route or sample envelope, not a biological taxon, ancestor sequence, global FAD/LAD or exact origin interval.