Microconchus/Spirorbis

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Microconchus sp.

Discussion:

This small fossil is a common member of late Pennsylvanian biotas. The producer is a
small worm-like animal that lived attached to a shell or other hard object by secreting
a coiled tube with a small opening. These fossils are usually identified as tubes produced
by an animal related to the living annelid worm Spirorbis. However, recent work has
shown that Pennsylvanian (and all pre-Cretaceous) specimens could not be formed by
Spirorbis worms (Taylor and Vinn, 2006). They were probably formed by worm-like
phoronids, a group related to brachiopods and bryozoans. The fossils should be identified
as Microconchus sp.

This specimen is distinctive in having prominent ridges circling the tube at regular intervals.
Most specimens of this fossil have smooth walls. The upward angled aperture opening
on the fossil is characteristic.

References:
Taylor, P.D. and O. Vinn, 2006, Convergent morphology in small spiral worm tubes
('Spirorbis') and its palaeoenvironmental implications; Journal of the Geological Society,
London, v. 163, p. 225-228.

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