Echinoids
(Class Echinoidea)
Burt Carter
Fall, 2012
Kingdom Animalia
Phylum Echinodermata
Animals with:
• Multi-plated skeletons of high-Mg calcite with a stereom microstructure.
• A water vascular system.
• (usually) pentameral symmetry superimposed on underlying bilaterality.
Class Echinoidea
Free-living echinoderms (“eleutherozoans”) with:
• the skeleton in the form of a test, which is usually (but not invariably) rigid.
• moveable spines articulated to tubercles on the test surface.
Taphonomy
•The high-Mg skeleton is mineralogically stable, allowing excellent preservation
in most cases. (So-called “perfect” preservation.)
• Diagenetic syntaxial cementation usually obscures the stereom
microstructure.
•Regular echinoids may have non-rigid tests, and in general the constituent
plates are not as well interconnected by connective tissue as in
irregular echinoids. Their fossil record is consequently not as
complete.
• Spines are articulated to tubercles only by connective tissue and the muscles
that operate the spines, thus they are often lost during biostratinomic
alteration. Their function may still be inferred from the muscle scars.
Periarchus pileussinensis (Ravenel, 1844)
#83015 in GSW taxonomic teaching collection
(labeled P. lyelli)
Anterior
Apical System
(Ocular and Genital
Pores evident)
Anterior
Location of
Mouth and
Peristome
Interambulacra
Aboral
View
Oral
View
Food
Grooves
Petals
(Petaloid Ambulacra)
Tubercles
(Completely Cover
Both Surfaces)
Posterior
Posterior
~2cm
(Most of the oral surface is covered by encrusting bryozoa.)
Location of
Anus and
Periproct
Borrowed from the Tree of Life website (tolweb.org)
References and Bibliography
Cooke, C.W., 1959, Cenozoic echinoids of eastern United States: USGS Prof. Pap. 321, 106 p.
Moore, R.C. (ed.), 1966, Treatise on Invertebrate Paleontology, part U, Echinodermata 3: Lawrence, KS, Univ. KS
press, 695 p.
Ravenel, E., 1844, Description of some new species of organic remains from the Eocene of South Carolina: Acad.
Nat. Sci. Philadelphia, Proc., v. 2, 96-98.
Smith, A.B., 1984, Echinoid Palaebiology, London, George Allen & Unwin Pub., 190 p.