This is Mazon Monday post #54. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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Octomedusa piekorum was described in 1968 in a paper by Ralph Gordon Johnson and Eugene S. Richardson, Jr. Both worked at the Field Museum of Natural History. The paper, "The Essex Fauna and Medusae", was published in the Museum's geology journal Fieldiana Geology. In that paper, Anthracomedusa turnbulli, a box jelly, was also described. O. pieckorum was dedicated to Ted and Helen Piecko, ESCONI members back in the 1950's and 1960's, who provided the first specimens to the Eugene Richardson at the Field Museum.
It's interesting so see that they were considered rare in the Essex biota. We know now that they are relatively rare compared to Essexella, but not so rare compared to some other animals.
Class Uncertain
Octomedusa, new genus
Figures 60-62
Since but a single species is known, the characterization of the genus must be the same as that of the species.
Genotype.—Octomedusa pieckorum, new species.
Description.—A small octagonal medusoid bearing eight tentacles of approximately equal length. The velum (or velarium) is narrow. A large central impression of the manubrium bears a cruciform mouth. Tentacles vary in length but do not exceed the diameter of the bell.
Holotype.—FMNH no. PE 11410, one-half of a small concretion collected by Mr. and Mrs. Ted Piecko from Pit 11 of the Peabody Coal Co., Essex, Illinois (fig. 60).
Paratypes.—FMNH nos. PE 11377 (fig. 61) and PE 11411 (fig. 62) collected from Pit 11 of the Peabody Coal Co., Essex, Illinois.
Discussion. —About 15 specimens of Octomedusa pieckorum have been examined. The diameter of the bell was found to range from 6.5 to 17.5 mm. The maximum length of the tentacles varies from 4 to 10 mm. In no instance do the tentacles exceed the diameter of the bell. The manubrium is represented by a square central impression about 1 by 1 mm. The width of the velum is from 1 to 2 mm.
Although Anthracomedusa and Octomedusa are rare in the Essex fauna, it is our impression that Anthracomedusa is the more abundant of the two. The preserved features of Octomedusa are so general that it is not possible to assign this jellyfish to either the Hydrozoa or Scyphozoa.
The trivial name is in honor of Mr. and Mrs. Ted Piecko, who donated the holotype to the Museum and who have aided our studies of the Essex fauna in many ways.
Octomedusa is included in the "ESCONI Keys to Mazon Creek Animals". There are even some nice drawings by Don Auler.
OCTOMEDUSA PIECKORUM
Octomedusa pieckorum of the order Coronate, is the smallest of the three described scyphozoan jellyfish. Seen in the concretion, the round-bodied medusa, often only a stain in the rock, generally shows no relief save one area. That distinctive area is the large mouth opening, centered in the impression, which displays 11 a characteristic plus sign or "x" pattern in relief. Because of its size, the creature has a relatively small manubrium. The main species identifying character istic is the presence, in a good specimen, of eight short arms, equidistantly spaced around the dome shaped bell. Not all specimens show the full complement of the eight tentacles. In an exceptional specimen, eight pedalia, each with a single short tentacle can be seen to alternate in spacing with eight marginal lappets around the circumference.
In the previously mentioned sample of Essex animals, this species accounted for only 6% of the 2500. It was first described in 1968.
Octomedusa appeared in the "The Mazon Creek Fossil Fauna".
Octomedusa pieckorum is the smallest of the three described scyphozoan sea jellies in this book. When seen in a concretion, the round-bodied medusa-often only a stain in the rock-generally shows no relief save one area. That distinctive area is a large mouth opening, centered in the impression, which displays a characteristic plus sign or X pattern in relief. Because of its size, the creature has a relatively small manubrium. In a good specimen, the appearance of eight short tentacles, equidistantly spaced around the cone-shaped bell, is the main species-identifying characteristic. Not all specimens show the full complement of eight tentacles. In an exceptional specimen, eight pedalia, each with a single short tentacle, can be seen to alternate in spacing with eight marginal lappets around the circumference.
In the previously mentioned sample of Essex animals (see page 3), this species accounted for only 0.3 percent of the 230,000 concretions bearing fossils.
Example specimens
