| Escumasia Temporal range: Moscovian PreꞒ Ꞓ O S D C P T J K Pg N | |
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| Fossil of Escumasia | |
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| Three Escumasia alongside individuals of Gilpichthys | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | incertae sedis |
| Genus: | †Escumasia Nitecki & Solem, 1973 |
| Species: | †E. roryi |
| Binomial name | |
| †Escumasia roryi Nitecki & Solem, 1973 | |
Escumasia roryi is a species of enigmatic animal from the Mazon Creek site. Due to the large quantity of fossils, it has acquired a common name, that being "wye" or "y-animal" in reference to its shape.
Description
Escumasia ranges from 7.5 cm (3.0 in) to 20.5 cm (8.1 in) in length, with a stalk and two long arms making up most of this. These arms show no adaptations for capturing prey, thus their function is unclear. While being covered in cnidocytes and therefore a cnidarian affinity was proposed, this theory is unlikely due to an apparent anal slit on one side of the trunk showing that the organism was likely bilateral and had a "through-gut". The mouth is likely represented by a broad slit between the arms. The stalk is elongate, however rarely appears complete in fossils. The base is a bulbous disc with seemingly no surface features.
Classification
While Escumasia does bear similarities with various cnidarians such as sea anemones, the presence of an anus and therefore a complete gut, alongside bilateral symmetry, makes this relationship problematic. Slight traces of a central cavity within the fossils suggest a large "gastric cavity", likely the stomach. While it shares many similarities with "coelenterates", its bilateral symmetry and through-gut suggest otherwise, and therefore it is currently classified as Animalia incertae sedis.
Etymology
The scientific name Escumasia roryi honours E. Scumas Rory, printer laureate of Illinois paleontology.
References
- ^ Nitecki, Matthew H.; Solem, Alan (1973). "A Problematic Organism from the Mazon Creek (Pennsylvanian) of Illinois". Journal of Paleontology. 47 (5): 903–907. ISSN 0022-3360. JSTOR 1303070.