Plicodendrocrinus

Classification
Phylum: Echinodermata
Class: Crinoidea
Order: Cladida
Family: Dendrocrinidae
Genus: Plicodendrocrinus Brower, 1995
Cincinnatian Species: Plicodendrocrinus casei

Geologic Range
Middle Ordovician – Late Silurian

Common Paleoecology
Plicodendrocrinus is an extinct genus of stationary intermediate-level epifaunal suspension feeders

Identification in Hand Sample:

  • Adult cup bearing strong stellate ridges; inferradianal absent; superradianal pentagonal, directly below C-ray radial
  • Mature anal sac elongates, with roughly straight sides; sac plates strongly plicate in adults, much wider than high, in regular columns
  • Column pentalobate, lacking pentameres
  • Infrabasal, basal, and radial plate circlets with five plates each
  • Radial facets narrow, horseshoe-shaped, smooth, inclined outwards at about 35-45 degrees below horizontal

Geographic Occurrences

Published Description

Brower (1995):

  • Dendrocrinids with adult cup bearing strong stellate ridges; inferradianal absent; superradianal pentagonal, directly below C-ray radial; radial facets narrow. Arms non-pinnulate, isotomous. Mature anal sac elongates, with roughly straight sides; sac plates strongly plicate in adults, much wider than high, in regular columns. Column pentalobate, lacking pentameres. Description. -Aboral cup of adult with sharp single or multiple stellate ridges; cup plates may also have small nodes or rugose markings; juvenile cup plates nodose or with median- ray ridges; aboral cup conical. Infrabasal, basal, and radial plate circlets with five plates each; inferradianal absent; superradianal pentagonal, located below C-ray radial. Anal X above truncated CD interray basal, between C and D ray radials. Radial facets narrow, horseshoe-shaped, smooth, inclined outwards at about 35-45 degrees below horizontal; radial facet width: radial width 0.40-0.65. Tegmen poorly known, mostly composed of irregular plates, not dominated by orals. Anal sac elongates, sides straight to slightly curved; anal sac plates much higher than wide, arranged in regular columns; number of columns on one side of anal sac ranges from four or five to about 12; adult anal sac plates strongly plicate; juvenile plates may be nodose or less plicate than in adults. Arms uniserial, not pinnulate, branching isotomously numerous times; adjacent arm branches separated by moderate number of plates. Aboral sides of proximal brachs in mature specimens commonly sharp, with flanges on distal margins; all brachs of juveniles and distal brachs of adults lack distal flanges and have round aboral sides. Articular surfaces poorly known, mostly smooth, some with small marginal rim. Column pentalobate, pentameres absent in all known parts of stem; lumen known in some species, pentagonal with points oriented in radial position as in normal dicyclic crinoids.

Treatise on Invertebrate Paleontology, Part T, Vol. 2(2) (1978):

  • (For Dendrocrinus) Crown elongate, slender. Cup high conical, with large radianal directly below C radial; anal X large, between posterior radials and supporting series of large anal plates at posterior base of anal sac, which is very elongate, tapering to a point distally, composed of several longitudinal rows of thin, plicate, laterally interlocking plates. Arms rounded, slender, branching several times isotomously; primibrachs 5 to 7 axillary. Radial articular facets narrow, rounded, with outward-downward slope and wide interradial notches. Stem circular transversely, tapering distally.

P. casei