Microconchus sp.
("Spirorbis sp.")Ibbenbüren
Westfalian B
Microconchus sp.
("Spirorbis sp.")
Ibbenbüren
Westfalian B
Until recently these small spiral-shaped organisms were considered to
be little worms with a chalk shell. Research has proved that they belong
to a different group. The strong resemblance with real Spirorbis,
which occurs from the Cretaceous on, is a case of convergent evolution.
The microstructure of the shell of the old "Spirorbis" is completely
different from the one of the extant Spirorbis. The old
"Spirorbis" belongs to the Microconchida, a group of organisms which
is related to the brachiopods and the bryozoans.
The new name of the genus is Microconchus. Fossils occur in sediments
from the Upper Ordovician until the Mid Jurassic. Another difference between
both groups is that Microconchus was living in freshwater whereas
Spirorbis was a sea animal.
Taylor, P.D. & Vinn, O. 2006. Convergent morphology in small spiral worm
tubes ("Spirorbis") and its palaeoenvironmental implications.
Journal of the Geological Society, London 163: p.225-228.