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The remains of a pterobranch hemichordate, recognized as numerous fragments of zooidal tubes and remnants
of the stolon system (i.e. stolons and capsules or cysts of dormant buds), were obtained by chemical isolation
from the early Llandovery limestone (Beescie Formation, member 4) from the well known locality named A5C on
the Island of Anticosti (Quebec, Canada). These fossils, referred to as a new species of the genus
Rhabdopleura, are first fossil representatives of the order Rhabdopleuroidea in North America. Previously,
similar forms were described from the Ordovician and Silurian of Baltoscandia as the thecate hydroid cnidarian
Kystodendron longicarpus (Eisenack) Kozłowski or the rhabdopleurid pterobranch Kystodendron longicarpus
(Eisenack) sensu Kozłowski. The skeletal material of the form under study was investigated using SEM
techniques. Fragments of zooidal tubes are built of typical erect and creeping parts, usually strongly flattened,
sometimes distorted, and revealing distinct fusellar structure similar as in other extinct and extant species of
Rhabdopleura. The periderm looks membraneous, amber brown, more or less translucent, provided with distinct
fusellar collars. The outer surface of zooidal tubes is devoid of pellicle or the pellicle is so delicate that it reflects
roughly the shape and orientation of underlying fusellar fibrils. Internal secondary deposits, composed of cortical
fibrils, arranged in parallel, similar to that in Recent Rhabdopleura compacta, are recognized on the inner
surface of zooidal tubes. This is the first finding of inner fibrillar secondary deposits in the fossil
Rhabdopleuroidea and these deposits are equivalent to true graptolite endocortex. The cortical fibrils, closely
packed or even cementated, were found also in fusellar collars. Cysts of dormant buds are subcylindrical,
variable in length (usually 0.6-0.8 mm long), closed or ending with terminal stolon. Peduncular stolon of cysts is
usually short, with constrictions and swellings, rapidly widening and passing into cysts.
of the stolon system (i.e. stolons and capsules or cysts of dormant buds), were obtained by chemical isolation
from the early Llandovery limestone (Beescie Formation, member 4) from the well known locality named A5C on
the Island of Anticosti (Quebec, Canada). These fossils, referred to as a new species of the genus
Rhabdopleura, are first fossil representatives of the order Rhabdopleuroidea in North America. Previously,
similar forms were described from the Ordovician and Silurian of Baltoscandia as the thecate hydroid cnidarian
Kystodendron longicarpus (Eisenack) Kozłowski or the rhabdopleurid pterobranch Kystodendron longicarpus
(Eisenack) sensu Kozłowski. The skeletal material of the form under study was investigated using SEM
techniques. Fragments of zooidal tubes are built of typical erect and creeping parts, usually strongly flattened,
sometimes distorted, and revealing distinct fusellar structure similar as in other extinct and extant species of
Rhabdopleura. The periderm looks membraneous, amber brown, more or less translucent, provided with distinct
fusellar collars. The outer surface of zooidal tubes is devoid of pellicle or the pellicle is so delicate that it reflects
roughly the shape and orientation of underlying fusellar fibrils. Internal secondary deposits, composed of cortical
fibrils, arranged in parallel, similar to that in Recent Rhabdopleura compacta, are recognized on the inner
surface of zooidal tubes. This is the first finding of inner fibrillar secondary deposits in the fossil
Rhabdopleuroidea and these deposits are equivalent to true graptolite endocortex. The cortical fibrils, closely
packed or even cementated, were found also in fusellar collars. Cysts of dormant buds are subcylindrical,
variable in length (usually 0.6-0.8 mm long), closed or ending with terminal stolon. Peduncular stolon of cysts is
usually short, with constrictions and swellings, rapidly widening and passing into cysts.
| GRAPTOLITE NET is edited and periodically updated by Piotr Mierzejewski, Count of Calmont and Countess Maja Korwin-Kossakowska since 2002 |
| FIRST OCCURENCE OF THE FOSSIL HEMICHORDATE RHABDOPLEURA (GRAPTOLITHOIDEA) IN NORTH AMERICA PIOTR MIERZEJEWSKI, CYPRIAN KULICKI and STEFANO SCHIAPARELLI North American Paleontology Convention 2005, Abstracts, pp.125-126 |
