The Geology of Delaware

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Starfish and Urchins: Phylum Echinodermata

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Phylum Echinodermata
Echinoderms are "spiny-skinned" invertebrate animals that live only in marine environments. Two major divisions are recognized by biologists: principally attached, usually stalked forms of the Pelmatozoa; and unattached free-moving forms of the Eleutherozoa.

Fossil Pelmatozoa are represented in Delaware by stem fragments or columnals from crinoids or sea lilies. Columnals belonging to the Cretaceous crinoid Dunnicrinus are common finds on the Reedy Point spoils. The calyx or head of this crinoid has not been found, probably because of its fragile nature.

Eleutherozoan fossils include a group of starfish-like, free-moving forms called brittle stars, and a group of armless spiny forms known as sea urchins. Complete sea urchins are rare and highly prized specimens. The most common finds along the canal are isolated spines and plates of sea urchins and small fragments of brittle stars.

Reference(s): 

Unless otherwise noted, photographs and figures are from DGS Special Publication No. 18, by E. M. Lauginiger, 1988.

Photo Gallery
1, 2. Hemiaster delawarensis - specimens from the Mount Laurel Formation<br>3, 4. Catopygus williamsi - specimens from the Mount Laurel Formation<br>5, 6. Phymosoma sp. - specimens from the Mount Laurel Formation<br>7. Dunnicrinus sp. - specimen from the Mount Laurel Formation<br>8, 9. Boletechinus sp. - specimens from the Mount Laurel Formation?<br>
Dunnicrinus sp. - occurs in the Mount Laurel Formation<br>Echinoid spine and plate - occur in the Mount Laurel Formation<br>Hemiaster delawarensis - occurs in the Mount Laurel Formation<br>Catopygus williamsi - occurs in the Mount Laurel Formation<br>Phymosoma sp. - occurs in the Mount Laurel Formation<br>Boletechinus sp. - occurs in the Mount Laurel Formation<br>
2. Hemiaster sp. - specimen from the Englishtown Formation<br>Cretaceous Echinodermata photograph from Plate I, DGS Report of Investigations No. 21, by T. E. Pickett, 1972.
1a, 1b. Hemiaster sp. - specimens from the Mount Laurel Formation<br>Cretaceous Echinodermata photographs from Plate VI, DGS Report of Investigations No. 21, by T. E. Pickett, 1972.