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Crystallographic Data for Echinoid Coronal Plates

David M. Raup
Journal of Paleontology
Vol. 40, No. 3 (May, 1966), pp. 555-568
Stable URL: http://www.jstor.org/stable/1301740
Page Count: 14
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Crystallographic Data for Echinoid Coronal Plates
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Abstract

Crystal orientation data for ambulacral and interambulacral plates of 135 fossil and Recent species are presented. This brings the total number of species with known coronal plate crystallography to 252. The new sample is dominated by species that have either perpendicular, tangential, or a combination of perpendicular and tangential c-axes in the coronal plates. Seventeen species in six families, however, exhibit ontogenetic variation in crystal orientation. Ontogenetic variation in the Arbaciidae and Toxopneustidae is distinct from that in the Echinometridae, Strongylocentrotidae, Conulidae, and Oligopygidae. The new data support the placement of the Oligopygidae in the order Holectypoida (as suggested by Durham & Melville, 1957) but raise questions as to the oligopygid affinities of the genus Haimea. The family Arbaciidae is extremely heterogeneous crystallographically; the data suggest that the family is polyphyletic. Variation in arbaciid crystallography is in good agreement with Mortensen's informal division of the family into five "groups."

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