Graptovermida by Piotr Mierzejewski

Graptolite Net

The Graptovermida are extremely rare and poorly known Ordovician and Silurian organic microfossils. These enigmatic forms were described by Kozłowski (1949) as a provisional group of marine invertebrates in some way related to pterobranchs and graptolites. To date, graptovermids have been known from the early Ordovician of Poland (Kozłowski 1949) and Öland, Sweden (Mierzejewski 1988). Recently, they were found in the early Silurian of Gotland, Sweden (Mierzejewski & Kulicki, in preparation). The alleged graptovermids of Skevington (1965) were reinterpreted as rhabdopleurid zooidal tubes by Andres (1977) and Mierzejewski (1977).

To the right is a specimen of Graptovermis intestinalis Kozłowski, 1949, from the Tremadoc of Poland (from Kozłowski).

 Bulman (1970) tentatively placed the Graptovermida in the Graptolithina incertae sedis. He described the only known genus Graptovermis Kozłowski, 1949 as "Flexuous or irregularly coiled chitinous tubes with a diameter of 100 to 400 microns, attached by one surface; growth by addition of fusellar segments as in Graptolithina".

According to Mierzejewski (1988), SEM studies did not show the presence of the fusellar and cortical layers in the tube wall, and the substance of the tube appeared structureless. Lack of any traces of fusellar and cortical tissues precludes homology of the graptovermid tube wall and the typical graptolite periderm. However, the fusellar-like pattern on the convex surface of graptovermid tubes suggests a close relation to the graptolite fusellar tissue. This alleged paradox is to dissolve if one compare graptovermids to graptoblasts. According to Urbanek, Mierzejewski & Rickards (1986) the graptoblast wall is composed of two layers: blastocrypt (inner layer) and blastotheca (outer layer). The blastocrypt is made of electron dense and homogeneous material whereas the blastotheca is composed of fuselli. Fuselli of the blastotheca produce imprints on the upper surface of the blastocrypt in the form of shallow furrows and gentle elevations. These similarities in the fine structure of the blastocrypt and graptovermid tubes should be regarded as homologous. Mierzejewski (1988) supposed that graptovermids, similarly as graptoblasts, should be treated as resting stolothecae of encrusting graptolites. One may expect finding of graptovermids with preserved fusellar layer corresponding to the graptoblast blastotheca. Presumably, graptovermids have their equivalent in coenecia of the the extant genus Rhabdopleura.