Cincinnaticrinus pentagonus

C pentagonus 250px

Classification
Phylum: Echinodermata
Class: Crinoidea
Order: Disparida
Family: Heterocrinidae
Genus: Cincinnaticrinus
Species: Cincinnaticrinus pentagonus (Ulrich, 1882)

Taxonomic Details

Formerly: Heterocrinus juvenis Hall; Meek and Heterocrinus pentagonus Ulrich

Stratigraphic Occurrences

C.pentagonus_strat

Geographic Occurrences

Map point data provided by iDigBio.

Stratigraphic Description

Sequences (Formations)

  • C6 Sequence
  • C5 Sequence (Liberty, Waynesville)
  • C4 Sequence
  • C3 Sequence (Corryville)

Identification in Hand Sample

  • The columnals of C. pentagonus are larger than those of C. varibrachialus but are virtually identical in form
  • Cup is only 1.4 times wider than the proximal stem in uncrushed specimens
  • Often in non-pristine specimens, the cup is no wider than the diameter of the stem
  • 10, very slender arms
  • The distinction between C. pentagonus and C. varibrachialus may be artificial because there is a continual gradient of calyx diameter to stem diameter ratio and columnal size

Cincinnaticrinus pentagonus from Liberty formation of Franklin County, Indiana (OUIP 2217)

Published Description

Deline (2006):

  • Discussion: Cincinnaticrinus pentagonus is quite similar morphologically to Cincinnaticrinus varibrachialus and ranges from the Maysville to the Whitewater member of the Richmond. There is no addition of plates in the calyx during ontogeny, such that the plate structure of small individuals is the same as mature individuals (Warn and Strimple, 1977). The columnals of C. pentagonus are larger than those of C. varibrachialus but are virtually identical in form. The most visible difference between C. pentagonus and C. variabrachialus is the ratio between the diameter of the proximal stem and the diameter of the cup. Cincinnaticrinus variabrachialus flares out from the stem to the cup, but in C. pentagonus the cup is only 1.4 times wider than the proximal stem in uncrushed specimens (Warn and Strimple, 1977) and often in non-pristine specimens the cup is no wider than the diameter of the stem. The distinction between the two species may be artificial because there is a continual gradient of calyx diameter to stem diameter ratio and columnal size. The gradient in columnal size is well illustrated in this study. Warn and Strimple (1977) hypothesized that C. varibrachialus is ancestral to C. pentagonus and the size change might be linked to an increase in current activity.

Fossils of Ohio (1996):

  • Characterized by an extremely small, very short, cylindrical aboral cup that is typically not wider than the column. It has very slender arms. The column of C. pentagonus is quite distinctive; columnals are circular and have highly rounded edges.

Ulrich (1882):

  • Body small, a little longer than wide, with the breadth but slightly more above than below, in some specimens a little constricted above at the point where the rays become free; in old examples, pentalobate, as seen from below, in consequence of each radial series being convex, and the vertical sutures between them a little excavated. Basal pieces comparatively large, a little wider than high, with a general pentagonal outline. First radial in the central and left anterior rays, and the left posterior ray, convex, longer than wide, and supporting another shorter piece above, that tapers more or less upward, and upon this rest, in direct succession, three other plates, that are considerably wider than long, the third one being auxiliary and supporting two arms. . Right anterior ray with the first piece scarcely wider than long, and supporting in direct succession, two other slightly shorter pieces, the last of which tapers slightly upward, and again supports in succession, two still shorter pieces, and a third axillary piece. Right posterior ray, with the first piece slightly wider than long, while it supports above a somewhat smaller pentagonal piece, which in its turn again supports a smaller third radial, and on its left superior sloping side the first anal piece e; above the third radial piece there are in direct succession three short pieces, and a fourth axillary piece, which, as in the other rays, supports two arms.
  • Arms ten, rather slender , of moderate length; above their origin on the last of the primary radial series, rounded, and composed of piece usually a little wider than long, of which the third, and subsequently every fourth one, gives off on alternate sides of the arm, an armlet or branch nearly two-thirds as large as the main arm above; armlets composed of pieces that are as long as those of the main arm, being, in consequence, considerably longer than wide.
  • Column proportionally large, its diameter equaling two-thirds of that of the body at its widest point; distinctly pentagonal, with slightly prominent angles, and composed of alternating thinner and thicker disks; of the latter there are nine in the space of .3 inch below the basal plates. At a point about three inches below the body the column becomes rounded and the disks subequal.
  • Length of body, .2 inch; breadth, about .17 inch; length from last disk of column to first bifurcation, about .35 inch; length of arms, as far as observed, .62 inch: diameter of column, .12 inch. This species is closely allied, in some respects, to Heterocrinus juvenis, Hall, from which it differs in its less slender and longer arms, comparatively smaller, and pentagonal instead of rounded column, and slightly in the plates of the body. The three specimens examined were collected by Mr. George Oeh, who also discovered the preceding species. Formation and locality : Cincinnati group, at Cincinnati, Ohio, about 375 feet above low-water mark in the Ohio river.