Etacystis

Add links
Source: Wikipedia, the free encyclopedia.

Etacystis communis
Temporal range: Middle Pennsylvanian
Scientific classification
Kingdom:
Animalia
Subkingdom:
Eumetazoa
Phylum:
Hemichordata
?
Class:
Pterobranchia?
Genus:
Etacystis

Nitecki &
Schram
, 1976
Species:
E. communis
Binomial name
Etacystis communis
Nitecki & Schram, 1976

Etacystis communis, colloquially known as the H-animal or aitch,

hydrozoan affinity. Examples of Etacystis have been found only in the Mazon Creek fossil beds
of the Midwestern United States.

Etymology

Etacystis communis takes its genus name from its shape, being roughly similar in shape to the letter "H". Eta is the Greek letter "H" while cystis, from the Greek kystis, 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.[2]

Description

Etacystis 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 stolon-like structure from which a peduncle 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.

Relatively large for the animals of its time, Etacystis 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 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.[2]

Affinity

There is insufficient evidence to align Etacystis to any

Hemichordata which includes the acorn worms, and an affinity to this group is considered likely. The organism may have a close affinity to the Pterobranchia class, which likely includes the graptolite 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.[2] An alternate opinion considers Etacystis to be a hydrozoan, provisionally in the Siphonophorae.[3]

See also

References

  1. ^ Sula, Mike (July 1, 2004). "The Vanishing Mother Lode of Mazon Creek". Chicago Reader.
  2. ^
    JSTOR 1303556
    .
  3. ISBN 978-1-4832-5788-4
    .
Retrieved from "https://en.wikipedia.org/w/index.php?title=Etacystis&oldid=1172260677"