2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 4
Presentation Time: 8:00 AM-12:00 PM


CLARK II, George R., Department of Geology, Kansas State Univ, 108 Thompson Hall, Manhattan, KS 66506, grc@ksu.edu

In previous reports I have described the physical appearance and nature of the organic matrix associated with calcium carbonate skeletons in mollusks, brachiopods, bryozoans, foraminifera, and cirriped arthropods. Even though the distribution of matrix within the skeletons can differ considerably, as in the distinctive intercrystalline sheaths of mollusks and brachiopods, the ultrastructure and the dispersal of the intracrystalline matrix seem to be remarkably consistent. For example, the smallest components seem always to be nodular strands some 0.03 micrometers in diameter, and the first degree of complexity is nearly always the formation of a two-dimensional, lace-like mesh.

In this report I can add examples from the Porifera and Cnidaria. Although the individual spicules of sponges such as Leucosolenia and Grantia show no signs of internal matrix, the more massive sclerosponges such as Ceratoporella exhibit typical lacy meshworks of matrix. Moreover, some fossil sponges, including Paleozoic Girtyocoelia, Chaetetes, and an unidentified stromatoporoid, have preserved matrix remnants dispersed through recrystallized calcite skeletons. Among cnidarians, the hydrozoans Millepora and Stylaster have matrix, although irregular, while the octocorals Eugorgia and Tubipora, and the scleractinians Oculina and Paracyathus, exhibit a very characteristic lacy mesh. Even a member of the Rugosa, an unidentified horn coral from the Silurian of Gotland, shows remnants of a lacy matrix dispersed through a blocky calcite skeleton.

The physical attributes of the organic matrix observed in these two phyla fit nicely with the general trend of a fundamentally identical material being adapted to more complex functions by the more complex groups of organisms. An unexpected result is the startling capacity for preservation, at least physically, of these organic components.