SOFT-BODY PRESERVATION OF METACONULARIA

Several specimens belonging to a species of Metaconularia have recently been discovered in the Silurian Scotch Grove Formation of Iowa, from a site yielding exceptionally preserved fossils belonging to a variety of taxa. These conulariids exhibit unusual preservation in a number of regards. Some are preserved on their sides with the apical end at one end of the specimen and the aperture at the other, as is the case in most conulariids. Others have been transversely flattened with tears along the midlines in the apertural ends of the faces, yielding a Maltese Cross-like appearance. One specimen shows the replication in silica of a series of tear-shape pouches accompanied by thinner canals that were associated with the corners, that apparently radiated from the central axis of the animal. These tissues were evidently deformed and incompletely preserved, hindering straightforward interpretation, but preliminary analysis suggests that there may have been four of the thinner canals, each separating a set of four of the larger pouches. This may accord with the four radial canals associated with muscle bands, and gut partitioned into four radial pockets seen in adult Stauromedusae (and in adult pelagic Cubomedusae), but only if each gut pocket were subdivided into a further four pouches. Another possibility is that the pouches housed gonads. Although we have yet to recognize definitive synapomorphies linking this specimen to extant groups, the radial symmetry evident in the soft tissues supports a cnidarian-grade affinity.