Naedyceras Group

Naedyceras Group Temporal range: M Devonian
Scientific classification
Kingdom:	Animalia
Phylum:	Mollusca
Class:	Cephalopoda
Subclass:	Nautiloidea
Order:	Oncocerida
Family:	Brevicoceratidae
Genera
Naedyceras, Gonionaedyceras, Gyronaedyceras

The Naedyceras group is made up of three similar and closely related genera, Naedyceras, Gonionaedyceras, and Gyronaedyceras; three gyroconic members of the Brevicoceratidae, within the nautiloid order Oncocerida.

Naedyceras was named by Hyatt in 1884; Gonionaedyceras, and Gyronaedyceras by Flower in 1945. All three have open, gyroconic coiling, a subtriangular whorl section with a flattened dorsum. The siphuncle in each is ventral with flared out, cyrochoanitic septal necks and inwardly radial, blade-like actinosiphonate developments. All three come from the Middle Devonian of N Am, specifically New York, Ohio, and Wisconsin. Differences lie primarily in the symmetry of the whorl section and in the suture.

Genera

Naedyceras

Naedyceras is a brevicoceratid described as low-spired, loosely coiled dextral torticones with flattned dorsum and subtriangular whorl section. The body chamber bulges slightly. The aperture in mature specimens is somewhat contracted. Sutures form slight lateral lobes, dorsal lobed, and broad ventral and umbilical saddles. Whorl section is symmetric

Gonionaedyceras

Gonionaedyceras: strongly curved cyrtoconic brevicoceratids with an asymmetric subtriangular transverse section; obliquely flattened inside, dorsal, curvature and narrowed outside, ventral, curvature with a rounded to angular ridge not in the plane of the siphuncle. Sutures have dorsal and lateral lobes and umbilical and ventral saddles. Umbilical saddles are sharper on the left than on the right. Ventral saddles are rounded.

Gyronaedyceras

Gyronaedyceras; Compressed gyroconic brevicoceratids of about 2 volutions with an assymmnetrical, subtraingular whorl section having a broadly rounded to subangular venter and flat dorsum. Sutures are essentially straight and transverse. Actinosphonate structures are discretely developed.

Comparison

Naedyceras, especially, resembles Stereotoceras outwardly. Stereotoceras has a depressed, wider than high, cross section and a nummuloidal, beaded, siphuncle. Oxygonioceras is another loosely coiled brevicoceratid but with the dorsum rounded rather than flat.

References

• Sweet W.C. 1964. Nautiloidea -Oncocerida;Treatise on Invertebrate Paleontology Part K,Mollusca 3, K277-K317