Cupulocrinus polydactylus
Dendrocrinus caduceus
Merocrinus curtus
Plicodendrocrinus casei
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. Merocrinus is one of the few
crinoids in the Cincinnatian that possesses a spiral anal sac (not
visible in the specimens shown). 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. |
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