Invertebrates

Sea Urchins

 Sea urchins are members of a much larger group of marine animals called echinoderms. These include sea stars, brittle stars, crinoids and sea cucumbers. The fossil record shows divergence from sea stars nearly 450 million years ago in the late Ordovician period. It is believed that during the Cretaceous period, sea level rise may have accounted for a dramatic increase in their diversity. There are about 7000 extinct species of sea urchins and about 900 living species. The sea urchin shell or skeleton is called a test, which protects the soft internal organs, and is covered with spines arranged in five broad areas that are separated by narrow unprotected areas. The mouth, on the underside of the body, has a complex dental apparatus called Aristotle's lantern. A number of species have been reported from the New Jersey area, usually fragments, or of very poor quality. The spines of the sea urchin are common in some locations but because of their fragile nature are normally found broken.

Typical finds from Monmouth County, NJ.
The spines can be very common in some locations.
 

The only specimen of a sea urchin shell from Monmouth County, NJ
that we have found.
Measures 3/8th of an inch, 10mm across and is of very
poor quality.
 

The sea urchin shell or skeleton is called a test, which protects the
soft internal organs, and is covered with spines arranged in five broad
areas that are separated by narrow unprotected areas.
Clypeus plotti
France, Middle Jurassic

Catopygus columbarius, this particular species has been
reported from NJ.
Specimen from Normandy, France
Cretaceous
 

A view of the mouth on a fossilized sea urchin.
The entire chewing organ is known as Aristotle's lantern. So called from a
 reference by Aristotle to a sea urchin resembling in shape certain hand lanterns
of his time.