A Beginners Guide To Identifying Cincinnatian Crinoids

By Jack Kallmeyer

Inadunata - Cladida

Cupulocrinus polydactylus
Dendrocrinus caduceus
Merocrinus curtus
Plicodendrocrinus casei

Crinoid Anatomical Glossary

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Cupulocrinus polydactylus


10 mm scale
Photos by Jack Kallmeyer
Cupulocrinus polydactylus is easily identified by the smooth convex nature of the cup plates giving it the appearance of a bunch of grapes. C. polydactylus has a conical cup with thick arms supported by wide radial plates. The arms are non-pinnulate and divide multiple times above the cup.

The stem is round in cross-section and tapers gradually beneath the cup. Stem length is presumed to be quite short, less than 100 mm, based upon species of Cupulocrinus found in other parts of the country.

C. polydactylus is found in the Waynesville, Liberty and Whitewater Formations.

See photos of Cupulocrinus specimens found on Dry Dredgers field trips.

 

Dendrocrinus caduceus


10 mm scale
Photo by Jack Kallmeyer
Dendrocrinus caduceus has a somewhat conical smooth cup. The cup displays three dimples around the middle. The arms are narrower than the radial cup plates to which they attach.

The anal sac is large and consists of smooth plates near the top of the cup becoming more ornate distally.

The stem is round in cross-section and tapers beneath the cup.

Dendrocrinus caduceus is found in the Waynesville and Liberty Formations.

 

Merocrinus curtus


10 mm scale
Photos by Jack Kallmeyer
Despite the small cup size, the column of Merocrinus curtus can be up to a meter in length with column diameters up to 5 mm. Columnals are round in cross-section with a flat perimeter making the column exterior look smooth. Individual columnals are thin relative to their diameter. The column tapers to a smaller diameter towards the cup. The non-pinnulate arms branch above the cup with one branch being smaller in diameter than the other.

This small species is restricted to the Fulton Submember of the lowest Kope Formation.

Merocrinus curtus stems
10 mm scale
Photo by Jack Kallmeyer

Round very smooth stems.

 

Published reports of Merocrinus illustrate a large disc-like holdfast similar in appearance to “Podolithus,” a form genus for the holdfast of Anomalocrinus. This author has collected three examples of Merocrinus holdfasts comprised of distally coiled stems around other Merocrinus columns. These two holdfast types are problematic as crinoids generally maintain one specific form of attachment characteristic of their species.


10 mm scale
Photo by Jack Kallmeyer

The distal coil Merocrinus holdfast

10 mm scale
Cincinnati Museum Center
CMCIP 6432 with permission of Brenda Hunda

Photo by Jack Kallmeyer

Cemented holdfast of the form genus style called Podolithus.  This holdfast type is usually attributed to Anomalocrinus incurvus.  The specimen pictured  has been identified as belonging to Merocrinus curtus because the stem resembles Merocrinus.  Unfortunately, it also resembles small Amomalocrinus stems.  See also, the distal coil Merocrinus holdfast at left and the discussion of this issue above.

 

Plicodendrocrinus casei


10 mm scale
Photos by Jack Kallmeyer

Adult Plicodendrocrinus cups are highly ornamented with prominent ridges. Small individuals lack these ridges. The non-pinnulate arms branch twice above the cup. The arms are narrow, being narrower than the radial plates of the cup to which they attach. The arm cross-section is somewhat cuneiform.

The prominent anal sac is very distinctive in this species. The sac is large, at least ten times the height of the cup, and ornamented with stellate ridges. This anal sac morphology is apparent even in small individuals.

Plicodendrocrinus casei is found in the Waynesville and Liberty Formations.


10 mm scale
Photos by Jack Kallmeyer

10 mm scale
Photos by Jack Kallmeyer


The stem of P. casei is stellate in cross-section with faint articulating ridges. The stem tapers below the cup. The morphology of P. casei columns shows an ability to allow a small amount of twisting. In general, twisting of crinoid columns is restricted by interlocking grooves and ridges to prevent the column from breaking from torsional forces. Discovery of this capability in P. casei is unique among crinoids.

5 mm scale
Photos by Jack Kallmeyer

The anchorage method is via radicular cirri emanating from the distal stem allowing the crinoid a means of attachment in soft sediments. This form of attachment was rare among Ordovician crinoids.

  Crinoid Anatomical Glossary

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