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	Drepanaspis gemuendenensis Drepanaspis gemuendenensis (image: Nat.Mus.Nat.Sci. Tokyo )
	Drepanaspis was a jawless (agnathid), armored fish from the Early Devonian period (419-380 mya). The  name is derived from aspis, "shield." It belonged to the phylum Chordata, the subphylum Vertebrata, the superclass Agnatha, the class Heterostraci, the order Pteraspidomorphes, and the family Psammosteidae.    The type fossil Drepanaspis Gemuendenensis was found in 1887 by Schlüter in the Early Devonian Hunsrück lagerstätte (fine-grained shales with exceptional preservation) along the Rhine River in Germany. Other fossils of Drepanaspis have come from Early  to Late Devonian deposits of North America, Russia, and Europe.         Drepanaspis was a bottom feeder with a flattened; heavily armored body, presenting a ray-like appearance. The head shield is broad and flattened, indicating a shift to a benthic (bottom-living) existence. Drepanaspis also had small, widely spaced eyes.  Its mouth faced upwards, unlike most other Heterostracans which had downward-facing mouths. Various finger-like plates, called oral plates, were attached to the mouth, acting either as a filter or a scoop.  Depanaspis also had a lateral-line sensing system. It may have been an ancestor of the giant, meter-long, Psammosteid heterostracans of the late Devonian period.           Heterostraci ("Different scales") lived in both marine and estuarine environments. First appearing in the Ordovician period (495-445 mya), they lasted into the late Devonian period (380-370 mya), when all taxa, except the family called Psammosteids, became extinct. The scales of heterostracans are distinct from those of other vertebrates, having three layers composed of dentine and aspidin, the latter being a cellular bony tissue unique to this class. The middle layer of the scales was honeycombed with tiny spaces called cancella.                References Elliott & Mark-Kurik; 2005. A review of the lateral line sensory system in psammosteid heterostracans.      .
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