LIFE HISTORY OF THE MISSISSIPPIAN CRINOID, BARYCRINUS, FROM HOLDFAST DEVELOPMENT

Ontogenetic changes of the holdfast of Barycrinus indicate a changing life mode from juvenile to adult. Juvenile holdfasts were encrusting, and the adult Barycrinus holdfast was a rhizoidal holdfast rooted in unconsolidated sediment. Barycrinus is a geographically widespread cladid crinoid from the Lower Mississippian in North America and western Europe. Among contemporary crinoids, the Barycrinus column is unique in possessing pentameres, and thus, holdfasts are identifiable because this stem construction extends into the holdfast. The juvenile holdfast is circular in shape at the distal end and encrusted on a hard surface. The adult rhizoidal holdfast is created from dististele cirri and functioned like roots to secure the crinoid. Because adult Barycrinus holdfasts were adapted for attachment on a variety of unconsolidated substrata, attachment of the juvenile to the substratum may have been perilous. Thus, similar to other benthos, it is hypothesized that the juvenile Barycrinus was a secondary tierer encrusting on a hard substratum above the sediment-water interface. The Barycrinus juvenile holdfasts are preserved unattached, but we speculate that it was attached to crinoid columns, algae, or brachiopods. In addition to the pentameric holdfasts of Barycrinus, other small, encrusting holdfasts exist within Lower Mississippian crinoid assemblages. Unfortunately, these other holdfasts lack diagnostic characters, so identification is not possible. Regardless, we suggest that these represent other crinoids with a similar life history to Barycrinus.