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Piotr Mierzejewski
Acta Palaeontologica Polonica 2003, 48, 1, 93-98
The camaroid graptolite Xenotheka klinostoma
Eisenack, 1937 is described from the lower Llanvirn
limestones of Gilbergabrottet, norther Ă–land,
Sweden. Two distinct autothecal morphs are
recognized: (1) normal morph (described for the
first time), i.e. an autotheca with an unsculptured
outer surface, devoid of both an outer lining and
autothecal occlusion, and inhabited by an active
zooid; and (2) sealed morph, i.e. an autotheca
coated and occluded, provided with a sculptured
outer lining made of verrucose fabric, and
inhabited by an inactive or dormant zooid. In
addition, the existence of a hypothetical (3)
unsealed morph or re-opened autotheca, devoid of an
autothecal occlusion but provided with an outer
lining, and inhabited by a reactivated zooid, is
predicted. The sealed morphs may represent an
adaptation which allowed their inhabitants to
survive adverse conditions.
The outer lining of Xenotheka is
compared with a peculiar outer membrane found in
the modern hemichordate Rhabdopleura, from the
intertidal zone of Fiji, and with camaroid
extracamaral tissue.
morph. Length 0.67 mm.
morph. Length 0.98 mm.
Abbreviations: d - vesicular diaphragm of
stolonal system; s - mould of the terminal
portion od the parental stolotheca (?); u-
upper surface of autotheca, note the presence
of fusellar bands.
morph. Note the presence of numerous
verrucae of the verrucose fabric.
Piotr Mierzejewski, the Count of Calmont and Goethe Lab - Centrum Paleobiologii
2003
