| 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 .
[TEXT]
The Ordovician microfossil Xenotheka is a camaroid graptolite.
Graptolite nature of the Ordovician microfossil 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 .
[TEXT]
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. |
