This is Mazon Monday post #64. What's your favorite Mazon Creek fossil? Tell us at email:[email protected].
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For Mazon Monday this week, we have a small filter feeding shrimp, which is one of the smallest known from the Mazon Creek fossil biota, Essoidea epiceron, was described in 1974 by Dr. Frederick Schram, who has described many fossil crustaceans including Kallidecthes richardsoni. This little guy appeared in "ESCONI Keys to Mazon Creek Animals" from 1989, "Richardson's Guide to the Fossil Fauna of Mazon Creek", and "The Mazon Creek Fossil Fauna". Excerpts are shown below.
From "ESCONI Keys to Mazon Creek Animals"... with excellent drawings by Don Auler.
This filter feeder is one of the smallest shrimp in the Essex Fauna, hence is often overlooked. Body preservation is good, leg preservation is not, due to fragility and small size. Oval carapace, half the length of the animal, is squarish in pro file, bearing prominent optic notch. The antennae are short. The first abdominal segment is relatively large and bulbous, the following segments are flexed down in a sinuous "S" curve, hence its generic name. This odd configuration is an aid in field identification. Elements of the tail-fan were sharply tapered. It lacked pleopods.
From "Richardson's Guide to the Fossil Fauna of Mazon Creek", chapter 12 "Crustaceans by Fredrich R. Schram, W. D. Ian Rolfe, and Andrew A. Hay
Essoidia epiceron Schram, 1974a Figures 12.24, 12.25
Small shrimp like form; rostrum moderately developed, prominent optic notch, carapace sub rectangular in outline without any decoration; thoracic legs long and delicate in form; abdomen with first segment greatly inflated, deflecting the distal parts of the abdomen downward; uropods bladelike; telson subrectangular, lateral margins serrate, the terminus is pointed and flanked by two pairs of spine like caudal furca.
This animal was placed among the "eocarids" but has many structural similarities to mysidan mysidaceans and may in fact be one. The animal is relatively rare among the Essex fauna crustaceans, though this fact may not reflect its original abundance since it was probably a pelagic form that was rarely preserved in the Essex biota.
From "The Mazon Creek Fossil Fauna", by Jack Wittry
A probable filter-feeder, Essoidia epiceron is one of the small est shrimp in the Essex Fauna, and is therefore frequently over looked. Body preservation is often good, but leg preservation is not, due to fragility and small size. The oval carapace-half the length of the animal-is squarish in profile, bearing a prominent optic notch. The antennae are short. The first segment of the pleon is relatively large and bulbous; the following segments are flexed down in a sinuous S curve, hence the common name, S-shrimp. This odd configuration is an aid in field identification. Elements of the tail fan are sharply tapered, and the pleopods are not known to be preserved.
Specimens
Recently opened from Pit 11
Same specimen, but from a microscope
From the web
