Middle – Late Ordovician
Philhedra is an extinct genus of stationary, epifaunal suspension feeders
Identification in Hand Sample:
- Small size
- Biconvex profile
- Circular to subcircular outline
- Dorsal valve is conical
- Ornamented by fine ribs radiating from apex of dorsal valve, and thick, radially aligned hollow spines
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- Philhedra was one of the few craniide survivors of the Late Ordovician crisis interval (Described in Rong et al., 2006).
- Bassett (2000, Treatise) considered Philhedra to be a monospecific genus.
- The most finely ribbed Paleozoic craniide species that were previously erroneously identified as Philhedra – which is characterized by a smooth shell and hollow spines – are probably assignable to Deliella Halamski, 2004.
- The diagnostic features of Philhedra Koken have remained poorly understood (e.g., Wright, 1972); Huene (1899) included several species that, although lacking spines, have a distinct costellate radial ornament. Bassett (2000) convincingly demonstrated that Philhedra baltica Koken, 1889, which is the type species of this genus, lacks a radial ornament but possesses long hollow spines covering the entire surface of the shell. Thus, Philhedra lonispina (Homer et al., 2013) is the only other species that can be confidently assigned to the genus, whereas all other existing record of Philhedra in the Silurian are doubtful and in need of revision.
Fossils of Ohio (1996):
- a small acrotretid brachiopod that as a circular to subcircular outline and a bi-convex profile.
The upper, brachial valve is conical. The beak is in the center of the valve. Characteristic is the presence
of numerous fine ribs radiating from the apex of the brachial valve. Philhedra is known from the
Treatise on Invertebrate Paleontology, Part H, Vol. 2 (2000):
- Dorsal valve subconical; beak well posterior with steep, concave posterior face; ornament of
thick, radially aligned hollow spines, concentric growth laminae; musculature unknown; encrusting;
ventral valve unknown.