Wooster’s Fossil of the Week: An echinoid from the Eocene of France

July 7th, 2013

newEchinolampas_ovalis_aboralThe above is a specimen of the echinoid Echinolampas ovalis (Bory de St Vincent, 1824) from the Eocene of Civrac-en-Médoc, France. We are looking at what is called the aboral surface — that part of the organism on the other side of its mouth. (I’m sure by now you recognize the little barnacle boring near the bottom of the skeleton.) Below is the oral view of the same specimen.

newEchinolampas_ovalis_oralEchinoids are a kind of echinoderm with a very long evolutionary history from the Ordovician to today. They include sea urchins, heart urchins and sad dollars, along with a few others. All echinoids are covered in life with numerous spines. These spines almost always fall off after the death of the organism, leaving the smooth test we see here. The tiny circles covering the surfaces of this specimen are spine attachments. In life this would have looked like a spiky ball.

In the center of the oral view is a large hole where the mouth was. The plates surrounding this are called the peristome (around-mouth). At the bottom on the oral view are two holes. The larger is where the anus was located (within the periproct of plates); the smaller is a circular boring, likely from a gastropod predator. Since the periproct is not in the center of the aboral surface, this is what is known as an irregular echinoid.
Echinolampas_ovalis_Eocene_Civrac-en-Médoc_France_CloseUp052013Above is a close-up of the center of the aboral surface. The radiating rows of holes were where tubefeet extended. These soft structures at the end of the water vascular system were used for locomotion, moving bits of food towards the mouth, and even respiration. The very center is a finely-porous plate called the madreporite (the opening for the water vascular system). The four holes around it are genital pores for releasing gametes into the water during reproduction. For a simple, globular organism, the echinoid is amazingly complex.
450px-Bory_Saint-Vincent_1778-1846Echinolampas ovalis was named by a scientist with a complex life story of his own. The dashing Jean Baptiste Bory de Saint-Vincent (1778-1846) was one of a remarkable generation of French zoologists. He began his career as a naturalist, studying the fauna on various French possessions in the Indian Ocean. He returned to France and became a soldier in the Napoleonic Wars, serving in the battles of Ulm (1805) and Austerlitz (1805), and participating in the disastrous French campaign in Spain. He was a Bonapartist to the end, opposing the Bourbon restoration, which resulted in exile from France. After his politics faded, he returned to France in 1820 and resumed his career as a traveling naturalist. He named dozens of living and fossil species of invertebrates after the wars, including our quiet little echinoid in 1824.

References:

Kier, P.M. 1962. Revision of the cassiduloid echinoids. Smithsonian Miscellaneous Collections 144(3), 262 pp.

Roman, J. 1965. Morphologie et evolution des Echinolampas (Echinides, Cassiduloides). Memoires du Museum National d’Histoire Naturelle, Nouvelle Serie, C, 15, 1-341.

Thum, A.B. and Allen, J.C. 1976. Reproductive ecology of the lamp urchin Echinolampas crassa (Bell), 1880 from a subtidal biogenous ripple train. Transactions of the Royal Society of South Africa 42: 23-33.

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