World Congress of Malacology Antwerp ... - Unitas Malacologica

In freshwater bivalves the outer mantle epithelium (OME) is the organ responsible for the control of
shell mineralization. The OME a) secretes the organic molecules where the precipitation of calcium
carbonate takes palace, b) maintains the calcium concentrations above saturation in the extrapaleal
compartment that is in contact with the shell, and c) regulates the pH of the extrapaleal compartment
that, by influencing the carbonate concentration, may thermodynamically force the reaction CaCO3 �
Ca 2+ + CO3 2- in one direction or the other.
In short circuit conditions, the OME transports protons at very high rates to the extrapaleal
compartment. This transport is due to the operation of a V-ATPase, bafilomycin sensitive and is
equivalent to the Isc generated by the OME. To evaluate the effect of TCCD on shell mineralization
we have studied its effect on the short circuit current (Isc) in vitro and in vivo. Using voltage clamp
technique the epithelium was mounted in Ussing type chamber and short circuited.
The 6 days exposure of the animals to TCDD (30 nM) resulted in an significantly increase (p< 0,05)
of the Isc when compared with control animals. The effect of TCDD on shell mineralization will be
discussed. The Isc may be a useful tool to study the effect of pollutants on shell mineralization.
Support: Reitoria-UP and CGD
A phylogeny of the minute thyasirids (Bivalvia: Thyasiridae) based on morphological
investigations
Barry, Peter 1 ; McCormack, Grace 2
1. Zoology Department, National University of Ireland, Galway, Ireland,
Email: peter.barry@nuigalway.ie
2. Molecular Evolution and Systematics Laboratory, National University of Ireland,
Galway, Ireland, Email: grace.mccormack@nuigalway.ie
The family Thyasiridae Dall, 1900, comprises twelve genera with approximately 90 species. A large
proportion of these species do not grow larger than 3 mm. A morphology-based phylogenetic
analysis focusing on the group currently included in the subfamily Axinopsidinae Bernard, 1983, was
undertaken to test the validity of this classification at subfamily level. This analysis utilized
characters coded from the external shell morphology and the internal anatomy. The external shell was
prepared for scanning electron microscopy by dissolving soft parts in 2 % sodium hypochlorite and
mounting the shell on stubs using a combination of adhesives. Investigating the internal anatomy,
traditional paraffin wax-based histological techniques proved unsuccessful. An alternative resinbased
technique proved more suitable for dealing with minute specimens. The full technique of using
resin-based histology will be outlined, including advantages and disadvantages. Using this
methodology a total of 75 diagnostic characters, 35 based on the external shell, 40 based on the
internal anatomy were scored for each specimen. Thirty one characters were deemed
phylogenetically informative and included in the analysis. In total 27 thyasirid species including four
putative new species were coded for phylogenetic analysis. The results of this phylogenetic analysis
suggest the subfamily Axinopsidinae, as it currently stands, is polyphyletic. A fundamental split in
the family Thyasiridae would appear to have come about through reduction and simplification of
anatomy among certain genera. A revised classification of the subfamily is proposed, restricted to
those genera which display neotenous characteristics only. Support for this hypothesis is evident from
both conchological and anatomical characteristics which will be discussed in conjunction with the
practical techniques that uncovered them.
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