5
network which in course of time developed into large, irregular
cushions or balls, often overgrowing mussels and barnacles
already living in the neighbourhood. The accompanying figure
gives an idea of how these minute animals within the course
of one year can accumulate to mighty colonies of 200 mm. and
more in length (Fig. 4).
Another settler, even the most rapid of them all, was the
barnacle Balanus crenatus Brug. Almost from the very begin
ning of the inundation young barnacles could be encountered
on any object lying between the tidemarks. All the samples
which came into my hands consisted of shells of the broad,
shield-like type, as are characteristic for specimens which have
sufficient room for individual expansion. The dimensions of
the 5 largest shells are (in mm)
Diameter in carino-rostral direction at top Id. at base Heiqht
13 24 14
11 22 13
14 22 12
11 22 11
9 15 10
The high, narrow, tube- or corolla-shaped individuals which
are so characteristic for specimens living in closely set crowds
on a restricted substratum, are quite unknown in the inun
dated area.
On the breeding of Balanus crenatus we have almost no
information. I only found an incidental remark by Broch
(Kükenthal-Krumbach, Handb. d. Zool. Bd. Ill, Lief. 5, 1927,
S. 533) that under favourable conditions B. crenatus in two
years can attain a height of 35 mm and a carino-rostral top-
diameter of about 15 mm. Meanwhile there can be no doubt
that the Walcheren barnacles are at most 12 months old, but
generally less, as during the winter reproduction is retarded
or even stopped. It is however, probable that breeding occurs
more or less in all seasons, for specimens of all ages between
a pin's head and a sixpence were living side by side towards
the end of the marine phase.
Oysters Ostrea edulis L.were much less frequent than
any of the preceding species. Small and fragile shells were
found locally hanging in the shrubs and lying on twigs on the
ground. Their dimensions vary between 38 and 24 mm. height
and 4228 mm. breadth. Some spat had fallen on Balanus
crenatus of good size (diameter circa 15 mm.) which is a proof
that the oysters settled a good long while later than the
barnacles. This is in agreement with the breeding habits of
