Name: Crinoids
- Actinocrinites gibsoni (Family Actinocrinitidae), Macrocrinus mundulus
pair (Family Batocrinidae), , Gastropod - Platyceras aequilateralis
Age: Lower
Mississippian Osagean Stage (345 m.y.a)
Size (25.4
mm = 1 inch): Actinocrinites: 90 mm by 55 mm with 4 mm attached stem,
Macrocrinus – 40 mm by 18 mm crown with 12 mm anal tube showing
and 40 mm of attached stem and 29 mm by 15 mm crown Platyceras: 35 mm
by 23 mm on a 115 mm by 125mm matrix
Location:
Crawfordsville,
Indiana
|  Description:
A fine example of pair of the Camerate crinoid Macrocrinus mundulus
(Family Batocrinidae), one of which displays the elongated anal
tube from the famous Crawfordsville crinoid beds. The large cronoid
is a member of the Family Actinocrinitidae known as Actinocrinites
gibsoni which has a gastropod known as Platyceras aequilateralis
contained within its arms. These gastropods were coprophagous, presumably
feeding upon the discharge from the anal pore of the crinoid. The
shape of these gastropods is thought to have been influenced by
the type of crinoid with which they were associated. This is one
of the larger members of the genus, but the largest members were
up to 8 cm long, probably too large to have lived the same sort
of existence. Preservation on this specimen is remarkably complete,
down to the fine pinnules on the arms, showing that it was buried
quite rapidly, preserving it from the decomposition and disarticulation
that usually is the fate of most echinoderms.
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