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Autothecal morphs and dormancy in the camaroid graptolite Xenotheka

Piotr Mierzejewski

Acta Palaeontologica Polonica 2003, 48, 1, 93-98
Abstract. 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.

         
R e l a t e d    p a g e s:

Autothecal morphs and dormancy in the camaroid graptolite Xenotheka .
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The Ordovician microfossil Xenotheka is a camaroid graptolite.

Graptolite nature of the Ordovician microfossil Xenotheka.
Upper view of isolated autotheca, normal
morph. Length  0.67 mm.
Lateral view of isolated autotheca, normal
morph. Length  0.98 mm.