Middle Ordovician – Early Silurian
Drepanella is an extinct genus of actively mobile epifaunal suspension feeders.
Identification in Hand Sample:
- Depressed convex.
- Suboblong valves have (more or less) complete, often sickle-shaped and sharply elevated marginal ridge.
- Two or more usually isolated nodes.
- Thick ventral edge.
- Depressed convex, suboblong valves with a more or less complete, often sickle-shaped, sharply elevated marginal ridge, within which the surface exhibits two or more usually isolated nodes; ventral edge thick; brood pouch unknown, probably wanting (Bassler and Kellett, 1934).
Fossils of Ohio (1996):
- Drepanella has a straight hinge and elongate ridges, nodes, and spines. It may be one of the most ornate ostracodes that you will find in the early Paleozoic rocks. It is restricted to Upper Ordovician rocks, such as the Whitewater Formation, in Ohio. Elsewhere this genus ranges from Mid Ordovician to Lower Silurian.
Treatise on Invertebrate Paleontology, Part Q, Arthropoda 3 (1961):
- Subrectangular to subquadrate; dorsal border straight, cardinal angles subequal, well defined; carinate rib subparallel to anterior and ventral free margin, terminating anterodorsally as spine which overreaches dorsal margin, prominent lobes in dorsomedial area separated by S2 lobes smooth or marked by small secondary spines, which may terminate dorsally in a spine; surface smooth, granular, or pitted; valves subequal; no velum or subcarinate ridges known. Hingement in RV consisting of long straight groove, corresponding bar presumed to exist in LV; dimorphism unknown.
- Carapace small, averaging 2.5 mm. long by 1.5 mm. high; subelliptical in outline; dorsal border straight, terminating abruptly at each end; ventral border nearly straight or gently convex, rounding almost evenly into the ends.
- Running nearly parallel with the posterior and ventral edges, a sharply-elevated sickle-shaped ridge, often produced spine-like beyond the postero-dorsal border. Dorsal slope with two or more strong tubercles or ridges. At the ventral edge the two valves meet equally.