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- Graptolite stolons described as hydroid remnants -
Fossil remnants of pterobranch and graptolite stolon system are moderately
common organic microfossils to be found in some marine deposits,
especially of Ordovician and Silurian age. However, they were repeatedly
misinterpreted for decades as remains of the "chitinous hydroids" or
incertae sedis forms. According to Mierzejewski (1986), such alleged
"hydroid" genera as
Calyxhydra Kozłowski, 1959, Cylindrotheca
Eisenack, 1934,
Kystodendron KozĹ‚owski, 1959, Lagenohydra KozĹ
‚owski, 1959,
Palaeotuba Eisenack, 1934,  and fossils described by KozĹ
‚owski (1959) as parataxonomic units Gonothecae Formae A, B, and C are
simply rhabdopleurid stolons and dormant bud capsules. Moreover, the
enigmatic
Xenocyathus stolonifer Eisenack, 1982, was recognized as a
fragment of the stolonal system of crustoid graptolites (Mierzejewski 1984).
Recently, another "hydroid" genus,
Diplohydra Kozłowski, 1959, was
also reinterpreted as an aberrant member of the Order
Rhabdopleuroidea
(Mierzejewski & Kulicki
2002).

   
To the right is the holotype of Trimerohydra glabra Kozłowski,
1959, the type species of the genus
Trimerohydra Kozłowski, 1959. This
form was described from Ordovician glacial  boulders of Baltic origin
collected in Poland, similarly as the second species of this genus,
T.
annulata
Kozłowski, 1959.The alleged hydroid nature of Trimerohydra
was questioned by Bulman (1970) in Treatise on Invertebrate
Paleontology
and regarded as a possible synonym of the graptolite genus
Koremagraptus Bulman, 1927.

   
Beneath is a fragment of a dendroid graptolite stipe showing  details of a
stolon trifurcation. The presented stolon are strikingly similar to the holotype
of
T. glabra.
R e l a t e d    p a g e s:

Graptolite stolons resembling tracheids of vascular plants.
Maenniligraptus ursulae - an Ordovician graptolite with a strange stolon system.
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Graptolite Net
Edited by
Piotr Mierzejewski,The Count of Calmont and Countess Maja Anna Korwin-Kossakowska


Some fragments of stolons of Trimerohydra glabra (= ? Koremagraptus sp.)
were studied with a transmission electron microscope  (
Mierzejewski 1986).
Ultrathin sections through the stolon  reveal that their walls are made of a
homogenous substance with rather uniform electron density, resembling the crassal
fabric of
Dictyonema and other sessile graptolites.
Photo: Cyprian Kulicki
Photo: Cyprian Kulicki
From R. Kozłowski