World Congress of Malacology Antwerp ... - Unitas Malacologica

High levels of intraspecific variation are also recognized in fossil taxa, suggesting that the broad
array of shell shapes observed today is not unique and likely represents a single species.
Using the PAM-technology as a tool to investigate the symbiosis between „solarpowered“
Nudibranchia (Gastropoda, Opisthobranchia) and Zooxanthellae (Dinophyceae)
Burghardt, Ingo
Department of Animal Evolution, Ecology and Biodiversity, Ruhr-University Bochum, D-44780
Bochum, Germany,
Email: ingo.burghardt@rub.de
A symbiosis with unicellular dinoflagellates of the genus Symbiodinium is known from different
marine invertebrates, including taxa within the Nudibranchia, especially the Aeolidoidea. The source
of these zooxanthellae in aeolids is mainly octocorals, on which the nudibranchs feed. Symbiodinium
is housed inside the cells of the nudibranchs digestive gland. This is affirmed for several species by
histological means. But the presence of zooxanthellae alone does not prove a mutualistic symbiosis.
By using the non-invasive PAM-Technology (“Pulse Amplitude Modulated Fluorometry”) it is
possible to distinguish between photosynthetically active and inactive zooxanthellae inside the
nudibranchs. The PAM detects in vivo photosynthetic activity of zooxanthellae by measuring the
fluorescence emitted by photosystem II (PSII) of chlorophyll a, the oxygen evolving site. About 1%
of the light absorbed by a photosynthetic symbiont will appear as chlorophyll a (chl a) fluorescence,
detected as emitted red light from PS II with maximum emission at 685 nm. By means of PAM-data
it is possible to estimate the efficiency of the symbiosis between a certain nudibranch species and its
zooxanthellae. Seven nudibranch species were investigated under starvation conditions (just relying
on the photosynthetic products of their symbiotic partner) and the maximum quantum yield of
fluorescence for PSII (ΦIIe-max) was plotted versus time in diagrams. Compared with histological
results, interspecific differences in the efficiency of symbiosis could be demonstrated. Generally the
branching grade of the digestive gland seems to be positively correlated with the efficiency of the
symbiosis. A strongly branched digestive gland offers the zooxanthellae a larger surface area that is
exposed to the sunlight and is typical for nudibranch species with a highly evolved and efficient
mutualistic symbiosis.
Discrimination of end-Cretaceous anodontine Unionoidea from North Dakota:
How many taxa make sense?
Burton-Kelly, Matthew; Hartman, Joseph H.
University of North Dakota Department of Geology and Geological Engineering,
81 Cornell Street, Stop 8358, Grand Forks, ND 58202 USA,
Email: matthew.burton.kelly@und.nodak.edu
The Das Goods Locality (L6516) is a remarkable site for the occurrence of anodontine (Unionoidea)
mussels. Stratigraphically just 63 cm between the Cretaceous-Paleogene boundary, it is the youngest
Cretaceous mussel locality. Even without shell material, this is the best-known record of in situ
anodontine bivalves from the Cretaceous of North America. There is little context for interpreting
other Late Cretaceous anodontine taxa. The earliest taxa described as anodontine were reported by
White in 1877 and 1878, respectively: Anodonta propatoris (Campanian Judith River Formation,
Montana) and A. parallela (Maastrichtian Laramie Formation, Colorado). Russell later (1935, 1932,
respectively) described poorly preserved Canadian taxa: A. johnseni (Campanian Milk River
Formation, Alberta), and A. argillensis and A. macconnelli (Maastrichtian Whitemud Formation,
Saskatchewan). L6516 bivalves are unsculptured and elliptical to ovate in marginal outline. External
growth lines are variously preserved. Because no landmark features are clearly available, identifying
characteristics are limited to the anodontine nature of the specimens and the shape of the marginal
outlines. Elliptical Fourier analysis (EFA) was performed on 33 specimens exhibiting a complete or
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