Foerstediscus cf grandis
Phylum Echinodermata, Subphylum Pelmatozoa, Class Edrioasteroidea
Geological Time: Middle Ordovician
Size (25.4 mm = 1 inch): Fossil is 26 mm across matrix: 160 mm by 110 mm
Fossil Site: Kirkland Formation, Kirkland, Ontario, Canada
Code: MMT149
Price: Sold
 Description:
This superb Echinoderm is a member of the Edrioasteroidea known
as Foerstediscus. This group of starfish relatives derives their
name from the Greek for seated star, and belies their sessile nature.
Unlike the highly mobile starfish, Edrioasteroids were attached
to a substrate by a short thick stalk covered with plates. The
ambulacra (radiating feeding grooves) were covered by large rooflike
plates which were capable of being raised, and were arrayed in
a characteristic spiral pattern. These echinoderms arose during
the Lower Cambrian, and survived until the Middle Pennsylvanian.
This one is unusual in that instead of the usual five ambulacra
there are six. Evidently at some point in its existence it sustained
an injury. Echinoderms are well known for their ability to regenerate
lost arms. This one grew an additional arm, making for an uncommon
specimen. Note too the hole in the specimen, this is not the result
of loss of any plates but moist likely a result of predation. Overall
a most unusual Edrioasteroid indeed. |
