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SNAILS, SHRIMPS AND AQUARETTES
Besides plants and fishes the pond should house
a variety of other creatures, not so much
because they are beautiful or interesting, but
because they will benefit her ladyship the
plant and his lordship the fish.
The molluscs, in which phylum of the
animal kingdom are included the cockle,
oyster, limpet, etc., provide the scavengers.
The freshwater snail is perhaps the best known
member of this fraternity and it is one of the
most useful. It lays a great quantity of eggs,
usually on the underside of lily leaves, and
fishes eat these with relish. The greatest
value of this animal, however, comes from its
' gleaning ' habits. The teeth are rasp-like
and are set in a flexible ribbon which the
creature can extrude or retract at will.
This ribbon, or tongue, is worked back-
wards and forwards as the snail pursues
its way, and the thin clean line so made is
quite noticeable.
The Ramshorn Snail
is the most common
species sold in England ;
it is a flat, convoluted
animal, dark brown in
colour with occasional
darker bands. The
shell itself has a number of small ridges across
it. Several other species are obtainable, one
in particular is quite handsome, being a deep
red colour. In the pool, of course, where the
snails are rarely seen, the common variety
suffices.
The Fresh-water Winkle (Paludina vivipara)
is a really pretty little chap ; the shell has a
fragile, semi-transparent look and the colour
is fawn with grey stripes. The shape is
pyramidal. The young are born alive in the
Summer and are recognisable as snails from
the onset. Fortunately, this snail never grows
to any size, for, although an efficient scavenger,
it is rather impatient and sets about the plants
before they have died.
The Limnae or Ear Snails are scavengers
also, but, from their greater size and slight
partiality for growing vegetation, should be
reserved for large ponds and lakes. In fact,
the Great Pond Snail (L. stagnalis) should
be introduced into
all large stretches of
water ; it will keep
the rapidly spreading
plants under control.
Six species of Limnae
inhabit the streams
and ponds of the countryside and all have
ear-shaped mouths. L. auricularia is the
most interesting species for the aquarium ;
it is as though made of horn and the mouth
is particularly large.
Physa, a closely related genus, has smaller
individuals and the shell is highly polished ;
moreover, the convolutions are left-handed.
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