Graptolite Net >> Graptolites & Graptoliters
|Autothecal morphs and dormancy in the camaroid graptolite Xenotheka
Acta Palaeontologica Polonica 2003, 48, 1, 93-98
|Xenotheka Eisenack is an encrusting graptolite of the order Camaroidea.
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.
|Upper view of isolated autotheca, normal
morph. Length 0.67 mm.
|Lateral view of isolated autotheca, normal
morph. Length 0.98 mm.
|Proximal part of autotheca, normal morph.
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.
|An occluded autothecal aperture of a sealed
morph. Note the presence of numerous
verrucae of the verrucose fabric.
|attachment surface (sole)