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Graptolite nature of the Ordovician microfossil Xenotheka

100%

Mierzejewski P.

Acta Palaeontologica Polonica

2000

tom 45

nr 1

71-84

Light microscopic, SEM and TEM investigations show that the periderm of the problematic Ordovician organic microfossil Xenotheka klinostoma Eisenack, 1937 is built of five layers: inner lining, endocortex, fusellum, ectocortex and outer lining. The outer lining is made of a previously unknown material named here verrucose fabric. The outer lining was presumably an adaptation which aided survival through periods of unfavourable conditions. The general morphology of the test as well as of the fusellar structure of the wall indicate that Xenotheka is an aberrant camaroid graptolite. This finding thus extends the upper stratigraphic limit of the order Camaroidea from the early Arenig to Llandeilo.

Autothecal morphs and dormancy in the camaroid graptolite Xenotheka

100%

Mierzejewski P.

Acta Palaeontologica Polonica

2003

tom 48

nr 1

The camaroid graptolite Xenotheka klinostoma Eisenack, 1937 is described from the lower Llanvirn limestones of Gilbergabrottet, northern Öland, 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 a unique 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.

Ograniczanie wyników

2 Acta Palaeontologica Polonica

2 Mierzejewski P.

1 2003

1 2000

Wyniki wyszukiwania

Graptolite nature of the Ordovician microfossil Xenotheka

Autothecal morphs and dormancy in the camaroid graptolite Xenotheka