Camerate and Cladid crinoids from the Upper Ordovician (Katian, Shermanian) Walcott-Rust Quarry of New York

Abstract

The camerates, Pycnocrinus argutus (Walcott, 1883) and Rhaphanocrinus subnodosus (Walcott, 1883), are characterized by narrow food grooves. An open distal stem coil was present in P. argutus, and R. subnodosus may have possessed the same type of holdfast. Such holdfasts either lay loose on the seafloor or were wrapped around unknown soft objects. The rhaphanocrinids were located at elevations of at least 300 mm above the substrate. Conversely, the much smaller pycnocrinids lived close to the seafloor at levels of about 10 to 24 mm. The three cladids are Merocrinus curtus (Ulrich, 1879), M. retractilis (Walcott, 1883), and Dendrocrinus gregarius Billings, 1857a. Merocrinus typus Walcott, 1883 and M. corroboratus Walcott, 1883 are conspecific with M. curtus. The spiral anal sac of M. retractilis is unique. Embryocrinus problematicus Hudson, 1918 probably represents a juvenile of Dendrocrinus gregarius, which also occurs in Ottawa, Ontario. Complete columns and attachment structures have not been found for D. gregarius and Merocrinus retractilis. Merocrinus curtus ranges from New York into the Cincinnati, Ohio area of the midcontinent. Although attachment devices and long stem segments are not preserved in the New York specimens, individuals of Merocrinus curtus from Cincinnati either have a conical holdfast cemented to a bryozoan or a tight distal stem coil that was wrapped around the stem of another crinoid; adult merocrinids from the Cincinnati region were positioned high above the seafloor, and incomplete stem segments up to about 800 mm long are known. The Walcott-Rust Quarry cladids all possessed wider food grooves than the camerates, so they were able to catch larger food particles.