MORPHOLOGY OF TUBULAR APPENDAGES AND REVISION OF THE GILBERTSOCRININAE

The Gilbertsocrininae represents a subfamily of diplobathrid camerate crinoids that includes the genera Lemmenocrinus Pidal, Moniellocrinus Pidal, Gilbertsocrinus Phillips, and Yunnanocrinus Chen and Yao from the Early Devonian (Emsian) to Middle Mississippian (Visean) of Africa, Asia, Europe, and North America. Gilbertsocrinus is among the most recognizable and remarkable of Paleozoic crinoid genera, in particular for the presence of ten tubular appendages that protrude from the calyx. Although the function of these appendages remains conjectural, examination of an ontogenetic series of individuals from the Silica Shale (Givetian) demonstrates that each appendage originates as a fixed pinnule that is roofed by tegmen plates.

Three generalized appendage configurations may be recognized among the Gilbertsocrininae. Tubular appendages may meet (1) interradially in all rays; (2) interradially in all but the CD interray; or (3) radially. For each configuration, adjacent appendages may or may not be fused into a single structure.

The tubular appendages of Gilbertsocrinus meet radially. However, all North American species currently assigned to the genus possess appendages that meet interradially in all or most rays. Most North American Devonian “Gilbertsocrinus” have appendages that meet interradially in all but the CD interray, and in most Mississippian species, the appendages meet interradially in all rays. Based on these observations and other characters, Goniasteroidocrinus Lyon and Casseday should be restored to receive Gilbertsocrininae with tubular appendages that meet interradially in all rays and possess invaginated infrabasals, and a new genus should be erected for those species with tubular appendages that meet interradially in all rays except the posterior. Thus, Gilbertsocrinus is not recognized from North America.

The oldest members of the subfamily, Lemmenocrinus and Moniellocrinus from the Early to Middle Devonian (Emsian-Givetian) of Spain, possess tubular appendage configurations like that of Goniasteroidocrinus. Younger Gilbertsocrininae, including Gilbertsocrinus from the Mississippian of England and Ireland, and Yunnanocrinus from the Mississippian of China, exhibit laterally unfused and fused appendages that meet radially.