World Congress of Malacology Antwerp ... - Unitas Malacologica

The Zebra mussel as a bioindicator for endocrine disruption? A study on the annual
gametogenic cycle and oestrogen levels in Dreissena polymorpha
Monsinjon, Tiphaine 1 ; Knigge, Thomas 1 ; Alain, Damien 1 ; Hill, Elizabeth M. 2 ; Minier,
Christophe 1
1. Laboratoire d´Ecotoxicologie Milieux Aquatiques, Université du Havre, 25 rue Philippe Lebon, BP
540, 76058 Le Havre, France,
Email: tiphaine.monsinjon@univ-lehavre.fr; thomas.knigge@univ-lehavre.fr; alain989@msn.com;
christophe.minier@univ-lehavre.fr
2. Centre for Environmental Research, School of Life Sciences, University of Sussex, Brighton. BN1
9QJ, UK,
Email: e.m.hill@sussex.ac.uk
Bivalve molluscs can be potentially exposed to high concentrations of waterborne estrogens in the
vicinity of sewage treatment plants. The zebra mussel is an abundant freshwater mollusc and, as a
sessile organism with a high filtration rate, it may be particularly useful to locate sources of
xenoestrogens. However, the effects of compounds with estrogenic activity on bivalve reproduction
are unclear. It is assumed that bivalves synthesise endogenous steroidal hormones and that they may
possess oestrogen receptors as well as vitellogenin-like proteins. This gives reason to hypothesise that
mussels are sensitive to endocrine disruption by steroid hormones, but the relation to vitellogenesis
and gonad development is not fully understood. As a background for evaluating possible effects of
estrogenic endocrine disrupting chemicals, we have investigated the gametogenic cycle of Dreissena
polymorpha (Pallas, 1771). Animals from an unpolluted reference site were monitored monthly over
more than one year. Histological samples of the gonads were analysed qualitatively to determine the
different developmental stages of the gonad. Quantitative histological analysis was conducted to
estimate the vitellogenic phase of oocyte development. Moreover, the gonad index was determined
and steroid levels were assessed.
The basic pattern of the reproductive cycle of D. polymorpha could be confirmed. After a resting
phase in late summer gametogenesis commenced in autumn with gametes developing throughout
winter until release in spring and summer. A rapid increase of the gonad index in February and
March clearly marked vitellogenesis. However, on the individual level, the picture was less clear. The
simultaneous occurrence of different development stages within the same animal confounded the
classification. These problems were resolved by the use of stereology. Nonetheless, it remained
difficult to correlate the highly variable levels of free oestrogen with oocyte development. In
summary, possible effects of xenoestrogen on gonad development of bivalve molluscs should be
elucidated for precisely determined gametogenic conditions.
Two new species of Phyllodesmium (Ehrenberg 1831) and a discussion of their placement within
the phylogeny
Moore, Elizabeth; Gosliner, Terrence
California Academy of Sciences, 875 Howard St., San Francisco, CA 94103,
Email: bmoore@calacademy.org; tgosliner@calacademy.org
The facelinid genus Phyllodesmium (Ehrenberg, 1831) consists of approximately 27 morphologically
diverse species that prey upon soft-bodied corals. At least 11 species have yet to be described,
making it an interesting genus for testing phylogenetic hypotheses. One of the most interesting
adaptations found in this genus is the widespread participation in a symbiotic relationship with
photosynthetic dinoflagellates in the genus Symbiodinium. Many species in Phyllodesmium are able
to retain zooxanthellae, which they obtain from their alcyonarian food source. A large degree of
anatomical adaptations that enhance the ability to retain zooxanthellae make this group an ideal place
to study the progression of symbiosis as it evolved in these animals. Histological studies have shown
a positive relationship between the extent of digestive gland branching and the zooxanthellae
retention abilities of these nudibranchs. Based on this observation, it is thought that animals with
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