World Congress of Malacology Antwerp ... - Unitas Malacologica

differentiation, is responsible for the among-population body-size variation. To explain the proximate
mechanisms of the variation, furthermore, I considered and examined two mutually non-exclusive
hypotheses: (1) body size of the individuals newly recruited into adult populations is smaller in
inshore habitats than in offshore habitats; (2) size-dependent adult mortality enhances the size
variation, i.e., larger adults are selected out in inshore habitats, and vice versa. A quadrat-based
monthly field research from February 2005 to February 2006 supported the first hypothesis, but the
second hypothesis was rejected by the mark-recapture sampling in inshore habitats. Consequently, I
concluded that the among-population size variation in Okinawa Island is primarily caused by the
phenotypic plasticity in size at maturity. I also propose a hypothesis that provides an adaptive
explanation on the observed pattern; smaller size at maturity may be a by-product of earlier
maturation and longer reproductive period, which is expected to be adaptive in inshore habitats where
a shorter lifetime is imposed.
The European bivalve Nucula nucleus (LINNAEUS) and its alleged fossil record – an example for
what we really know about the fossil history of our recent fauna
Janssen, Ronald
Forschungsinstitut Senckenberg, Senckenberganlage 25, D-60325 Frankfurt a. Main, Germany,
Email: ronald.janssen@senckenberg.de
The protobranch bivalve Nucula nucleus (LINNAEUS 1758) is a well known element of the marine
mollusc fauna of the European seas, widespread in the Eastern Atlantic from the North Sea to
Western Africa and in the Mediterranean Sea.
According to the paleontological literature the species formed already a regularly occurring
constituent of many fossil deposits as early as since the beginning of the Miocene (ca. 24 my). So we
can find records of it for the Early, Middle and Late Miocene as well as the Pliocene of the
Mediterranean province, further for the Early and Middle Miocene of the Paratethys basin and finally
for the Early Miocene until the Pliocene of the North Sea Basin. This fossil distribution seems to
show that the species represents an old European endemic faunal element with a broad adaptation to
subtropical to temperate resp. cool climates.
However, a critical survey of the fossil populations from various fossil localities and stratigraphical
stages from all European Miocene basins demonstrates that the picture is not as simple as supposed.
In fact it can be shown that the Miocene records apply to a number of different species, none of them
being closely related to N. nucleus. The first fossil occurrence which can be attributed with certainty
to that Recent species dates from the Pliocene (ca. 5 my). The example of N. nucleus demonstrates
how much basic taxonomical work still is needed to answer the question of the phylogenetical roots
of certain elements of our Recent European mollusc fauna.
What shall we do with the old descriptions?
Jensen, Kathe R.
Zoological Museum, Universitetsparken 15, DK-2100 Copenhagen Ø, Denmark,
Email: krjensen@snm.ku.dk
Collecting tiny, cryptically colored specimens from remote, difficult to access places is definitely a
major constraint on describing new species of Sacoglossa (Gastropoda, Opisthobranchia). However,
the detective work of finding old, inadequate descriptions of species, which have not been collected
since their original description, may also be a time consuming task. Many of these species have been
described from only a single preserved specimen and type material has not been deposited. In some
cases the original description does not include an illustration of a complete specimen, live or
preserved. The description itself often consists of only a few lines that can fit almost any species in
the genus or even family, or, conversely, does not seem to fit any species collected subsequently.
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