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Inner structure of Cretaceous insect egg Palaeoaldrovanda splendens Knobloch et Mai, studied using X-ray microtomography


Zuzana Heřmanová

Geoscience Research Reports 50, 2017, pages 99–102

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Published online: 29 June 2017

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Palaeoaldrovanda splendens Knobloch et Mai, 1984 was originally described as a fossil seed, closely related to the extant Aldrovanda vesiculosa (fam. Droseraceae). Fossil Palaeoaldrovanda splendens resembles seeds of Aldrovanda vesiculosa in its small size and black, shiny surface. However, reinvestigation of the fossil showed that Palaeoaldrovanda splendens differs from recent seeds of Aldrovanda vesiculosa in the following characters: micropylar area, hilum and wall structure. After a re­evaluation of all diagnostic features, it became clear that a close relationship between Palaeoaldrovanda splendens and Aldrovanda vesiculosa, as well as other Droseraceae, can be excluded. Several characters, such as wall structure and shape of the Palaeoaldrovanda’s projection indicate that the fossil is most likely an insect egg (Heřmanová - Kvaček 2010). Recently, their inner structures have been studied using nondestructive methods, and striking resemblances to insect eggs have been confirmed.
Fossil specimens of Palaeoaldrovanda splendens (Fig. 1) and extant insect egg of Lonchodes amaurops Westwood 1859 (Phasmatodea) (Fig. 3) were studied with a Bruker SkyScan 1172 x-ray microtomograph. X-ray tube intensity was 250 µA at 40 kV, and no filters were used. Rotation step size was 0.1- 0.5°, 2 or 3 frames for one step, random movement was 10 and 180° rotation was used. Effective pixel size was 0.54- 1.9 µm. N-Recon reconstruction software was used to process the raw data, and photographs were created with Avizo 9.1.1.
Several layers of egg shell: exochorion, endochorion and vitelline membrane, as well as possible embryo have been documented (Fig. 2). Fossil species Palaeoaldrovanda splendens Knobloch et Mai 1984 seems to be very similar to eggs of extant taxa of Lonchodes amaurops Westwood 1859 in general shape of embryo. However, recent L. amaurops, in contrast to the P. splendens, clearly show a micropylar plate on the outer surface. Palaeoaldrovanda splendens differ from L. amaurops in rectangular structure of the exochorion. Therefore, a relationship of P. splendens to order Phasmatodea is uncertain.


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