4
like queer fruit in the shrubs of gardens and groves (Fig. 2, 3).
The dimensions of 100 of the larger shells varied between
35 and 55 mm length and 18 to 24 mm height. Here we must
bear in mind that these specimens cannot be more than about
6 months old as the parent mussels breed at earliest in March.
Compared with the figures which Redeke mentioned in his
paper on the growth of Zuiderzee mussels (Versl. Staat Ned.
Zeevissch. 1910 (1911) Extra bijl. p. 89100) 5060 mm
at most in the first 8 months of their existence, it is evident
that our Walcheren mussels which approach these figures so
closely must have lived under almost optimal conditions. This
is also demonstrated by their form and texture rather thin,
slender shells, and colour plain light brown or straw-colour
with radiating brown stripes. Winterrings are missing.
The coating of the mussels on the houses and the pavements
on the ground had one advantage it formed a not unimpor
tant protection for the human settlements against the remor
seless violence of the waves.
The mussel communities in their turn afforded plenty of
opportunity for settling to other organisms. The increase of
surface attracted all sorts of sedentary animals and seaweed,
whereas the little nooks and crevices between the musselshells
were unsurpassed hiding places for motile creatures such as
worms, snails, crabs, isopods, amphipods etc., either in the
adult stage or as larvae. Thus the mussel zones called into
existence an entire association of organisms in which the
members although not directly advantageous to each other
live in a sort of tolerant companionship.
However, it is granted that it is not all roses and raptures
in this mussel population the apparently harmless lodgers
may turn out to be predators or parasites. Others are compe
titors in nutrition, straining off the fine microscopic plankton
organisms which also make the mussels' diet. A third danger
may arise from a too profuse settling of new organisms on the
top of the old ones. In this way the lower layers are likely to
be suffocated by the newcomers.
From a few samples, taken in October 1945 in the outskirts
of Middelburg, I could easily obtain a dozen species, some of
which will be discussed here.
One of the organisms which rapidly took advantage of the
new surroundings was the Polyzoon, Membranipora (Electra)
crustulenta (Pallas) var. fossacia (Hincks). Obviously it did
not settle on large, flat surfaces for colonizing, but preferred
branches of shrubs and rushes, starting as a thin, delicate
