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Dictyonal Structure in Hexactinosa and Lychniscosa

R. E. H. Reid
Journal of Paleontology
Vol. 37, No. 1 (Jan., 1963), pp. 212-217
Stable URL: http://www.jstor.org/stable/1301421
Page Count: 6
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Dictyonal Structure in Hexactinosa and Lychniscosa
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Abstract

Parenchymal frameworks of dictyonine Hexactinellida must not be regarded as constructed by tip to tip union of spicules. The basic mode of union, as stated by Zittel, is enclosure of two rays side by side in a common siliceous envelope. Other modes of union occur; but union of spicules tip to tip is not a normal occurrence. The formation of four-sided meshes is not the general basis of construction of the framework, as has formerly been believed; most three dimensional skeletons are correspondingly not composed of superimposed layers of meshwork, and instead are structures having fundamentally no stratified basis, or relation to cubic latticework. Correct analysis of structure requires reference to linear dictyonal strands, formed from series of dictyonalia; the most important factor is the way in which these strands are arranged. Hexactinosan skeletons are of three main types when judged on this basis, while most Lychniscosa show a structure which is comparable with the commonest hexactinosan type.

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