Previously unidentified tiny (about 0.5 mm in length), hollow, gently curved, serrated spines probably originally composed of horny, organic fibers from the Upper Mississippian (Middle Chesterian = Namurian A equivalent or lower Serpukhovian) of Arkansas (USA) are described, and their probable chaetognath affinities are discussed. The specimens are preserved in an oval accumulation (about 15 mm long and 6 mm wide) of approximately 200 specimens within a small (about 25 mm in length) phosphatic concretion. For comparison, the grasping spines of the Recent chaetognath Eukrohnia hamata were examined. The Arkansas specimens are named Eoserratosagitta serrata gen. et sp. nov., and this genus is assigned to the Phylum Chaetognatha. The Upper Mississippian spines are also compared with protoconodonts. This comparison supports the hypothesis that the chaetognaths may have existed in the Cambrian.

Key words: Chaetognatha, organic spines, protoconodonts, phosphatized fossils, Mississippian.

Larisa A. Doguzhaeva, [planetbond@mail.ru], Paleontological Institute of the Russian Academy of Sciences, Moscow, 123868, Russia; Harry Mutvei [harry.mutvei@nrm.se], Department of Palaeozoology, Swedish Museum of Natural History, SE−104 05, Stockholm, Sweden; Royal H. Mapes [mapes@ohiou.edu], Department of Geological Sciences, Ohio University, Athens 54701, USA.