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fossils of up to 11 cm have been known, with incomplete specimens considered to have been up to 15 cm in life. The holotype is 5 cm across from tip of sac to tip of arm, and the smallest specimens have measured as little as 2 cm. The H-animal is most likely a colonial organism
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arises at approximate right angles. The distal end of the peduncle has two arm-like extensions of unequal length, and a sac-like structure is attached to the peduncle by a short stalk, in the direction of the shorter of the two arms.
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that continued to grow throughout its lifetime, explaining the wide variation in specimen sizes found. The exact shape of the main sac varies significantly from specimen to specimen, from lobe-shaped to heart-shaped and others.
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organisms, however it is not certain if it belongs within the class or is a sister clade. The modern pterobranchs usually only grow to about a centimetre, unlike the relatively large H-animals. An alternate opinion considers
288:, means sac or bladder, referring to the organism's sac-like body plan. The specific name refers to the relatively common occurrence of the animal in the Mazon Creek fossil beds. Only a single species has been described.
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is an unusual animal of uncertain affinities, found among the Essex fauna of the Mazon Creek beds. It displays, as described above, a roughly H-shaped body plan. It has a
249:, about 300 million years ago. The classification is uncertain: the animal had a unique H-shaped body ranging from 2 to 11 cm long, and researchers have suggested a
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which includes the acorn worms, and an affinity to this group is considered likely. The organism may have a close affinity to the
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419:"Etacystis communis, a Fossil of Uncertain Affinities from the Mazon Creek Fauna (Pennsylvanian of Illinois)"
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with certainty. However, it is considered by
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takes its genus name from its shape, being roughly similar in shape to the letter "H".
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452:"Soft-bodied Coelenterates in the Pennsylvanian of Illinois"
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that lived in shallow tropical coastal waters of muddy
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Carboniferous invertebrate of unclear classification
417:Nitecki, Matthew H.; Schram, Frederick R. (1976).
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311:Relatively large for the animals of its time,
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393:"The Vanishing Mother Lode of Mazon Creek"
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324:There is insufficient evidence to align
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491:Enigmatic prehistoric animal genera
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340:class, which likely includes the
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454:. In Matthew H. Nitecki (ed.).
458:. Elsevier. pp. 191β267.
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280:is the Greek letter "H" while
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303:-like structure from which a
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261:have been found only in the
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391:Sula, Mike (July 1, 2004).
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450:Foster, Merril W. (1979).
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103:Scientific classification
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372:Paleontology in Illinois
424:Journal of Paleontology
353:, provisionally in the
263:Mazon Creek fossil beds
257:affinity. Examples of
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456:Mazon Creek Fossils
274:Etacystis communis
220:Etacystis communis
205:Etacystis communis
25:Etacystis communis
465:978-1-4832-5788-4
284:, from the Greek
247:geological period
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138:Hemichordata
121:Subkingdom:
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292:Description
242:during the
233:soft-bodied
480:Categories
378:References
342:graptolite
351:hydrozoan
347:Etacystis
326:Etacystis
313:Etacystis
297:Etacystis
269:Etymology
259:Etacystis
255:hydrozoan
240:estuaries
181:Species:
165:Etacystis
126:Eumetazoa
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361:See also
349:to be a
320:Affinity
305:peduncle
231:, was a
225:H-animal
133:Phylum:
114:Animalia
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328:to any
159:Genus:
146:Class:
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330:phylum
301:stolon
286:kystis
282:cystis
175:, 1976
173:Schram
433:JSTOR
229:aitch
460:ISBN
37:Preκ
278:Eta
253:or
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92:N
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42:κ
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