Class: Crinoidea Miller, 1821

Crinoids are a long-lived class of invertebrates with fossil remains found from Ordovician times to the current day. Researchers often find fossils of these marine creatures (nicknamed sea lilies) as small disc-shaped columnals with a central hole—the lumen. In life, muscle tissues hold together the columnal pieces in the stalk, making them flexible and allowing the crinoid to sway. They filter feed by capturing microscopic food particles from the water using the arms and pinnules, which transfer the food to the calyx.

The shape of the columnals—or the lumen—can help determine the genus, but not in a reliable way. All recovered columns and corresponding lumens from the Brush Creek limestone in Parks Township are circular. Plate specimens from the calyx, the central portion of the animal containing digestive organs, are scarce. In nearly all crinoid calyces, there are five basal plates where the stalk attaches, a layout similar to the arms of a starfish, another member of the Echinodermata. Adult animals in this phylum often have five-point radial symmetry.

Crinoid columnals from the animal’s stem are common and medium-sized in the Parks Township Brush Creek limestone. They are uncommon and small at the Kittanning Pine Creek limestone locale. Identification using only the columnal is nearly impossible at either location; you need the calyx to determine a species best. Other sites worldwide preserve specimens with articulated stacks of columnals with an attached calyx. The best local examples from this book’s two Armstrong County locales are only pieces.

The longest specimen found in four years of searching is a stack of 22 columnals (CG-0022) that measures 4 cm long. I have seen primarily disarticulated calyx pieces in the same period and only one near-complete calyx (CG-0695). The largest calyx petal (CG-0108) from the Brush Creek limestone has fascinating details, including a matrix of raised nodes across the face. CG-0033 is the crinoid columnal with the largest diameter. CG-0459 shows a cirrus scar, the place where cirri attach. These are arms that branch off of the central stalk. Columnals without cirri scars are called internodals.

Fig. 1.—A simplified crinoid morphology. Individual columns from the stalk are the most common to find as fossils. Calyx plates and small pieces from the arms are uncommon to rare. Entire articulated stalks with attached calyces exist in many horizons, but I have not seen one from Armstrong County.
Crinoid Calyx basal plate from the Brush Creek limestone. Genus indeterminate.
Fig. 2.—Crinoid Calyx basal plate from the Brush Creek limestone. Genus indeterminate. A–B, CG-0108. A, concave inside; B, convex outside with a matrix of raised nodes and brachial attachment along the base, CG-0108. Scale bar = 5 mm.
Crinoid columnals from the Brush Creek limestone SL 6533, Parks Township, PA.
Fig. 3—Crinoid columnals from the Brush Creek limestone SL 6533, Parks Township, PA. A, CG-0456; B, columnal with a cirrus scar, CG-0459; C, CG-0458; D, the largest in this collection from this location, CG-0033. Scale bar = 5 mm.
Crinoid Columnal stack from the Brush Creek limestone. Genus indeterminate.
Fig. 4.—Crinoid Columnal stack from the Brush Creek limestone. Genus indeterminate. Finding this many columnals together is rare in this location, this being the longest one found (4 cm) in four years of searching. Specimen CG-0022. Scale bar = 5 mm.
Crinoid specimens from the Brush Creek limestone at SL 6533 and the Pine Creek limestone at SL 6445
Fig. 5.—Crinoid specimens from the Brush Creek limestone at SL 6533 and the Pine Creek limestone at SL 6445. A–E, H, Columnals from SL 6533, A, CG-0465. B, CG-0468. C, CG-0466; D, columnal with very large lumen, CG-0469. E, CG-0467; H, a stack of columnals with a raised suture area, CG-0470. F–G, columninals from SL 6445, specimens appear smaller in size from this locality. F, CG-0474. G, perhaps part of the cirri, CG-0473; H, CG-0000. Scale bar = 5 mm.
Delocrinus sp. from the Pine Creek limestone at SL 64456. Species indeterminate.
Fig. 6.—Delocrinus sp. from the Pine Creek limestone at SL 64456. Species indeterminate. In four years of searching, this is the first near-complete Calyx found. Credit to Ben Neuman for locating it among Pine Creek debris. Specimen CG-0695. Scale bar = 5 mm.

References

Late Carboniferous Fossils from the Glenshaw Formation in Armstrong County, Pennsylvania

Localities: Locality SL 6445 | Locality SL 6533

Trilobita | Crinoidea

Bivalvia: Allopinna | Parallelodon | Septimyalina

Cephalopoda: Metacoceras

Gastropoda: Amphiscapha | Bellerophon | Cymatospira | Euphemites | Meekospira | Orthonychia | Patellilabia | Pharkidonotus | Retispira | Shansiella | Worthenia

Brachiopoda: Cancrinella | Composita | Isogramma | Linoproductus | Neospirifer | Parajuresania | Pulchratia

Chordata: Petalodus | Glikmanius