1—48
THE SEAS
these worms all “possess horny bristles which may. -‘as‘sist
them in burfoWing, it is probable that the greater part
this work is done by chemical means.
‘
But, as in the case of the wood borers, the largest and most
efcient rock bOrers are bivalve Molluscs. Of these the
largest is the familiar “ Piddock ” (Plate 55) which is a
stout bivalve with a white, spiny shell sometimes as mimh
as six inches long.
It, is distantly related to the ShipwofmŸ
and more nearly to the Other Wood-boring MolluscS.
It
bores by the rasping action of its shell, the rows of spines*
with which this is furnished gradually cutting into the rock
untii aburro'w of anything up to one foot in length, i‘n
the largest specimens, is constructed.
The Piddock is
;”
indierent as to the nature of the stone into which it bores,
«
it has been found ‘in limestone, sandstoue, Shale, miCaschist, pea-t and, very occasionally; wood.
In specimen‘s—
;
which bore into soit material the spines are long and ”pointed,
those taken from
they are round and
During the operation of»borig, the head of the butr0‘W'
is held by the sucker:—sha@ed foot, as in "the Shipwo'rmÿ
while_thé shell/twistSpand rocks.— on this .fulcrum. There
are limits;
thè-e’iciéhcy of this apparatus be- ir
cause thePiddockis never f0nndbŒing in‘theVeryha‘r'dæt
type
:.jMoreover, though the head of the burtoW "
_
mechanical action of the”
èÏâdf»©f;* @@
m mdth ;Ï
as
so;
:‘that there mûstb6
some kmdofcemmalawtumfmronly'chesofteshyS1phm&S
A pecuhar
ftufthPddkth…thtthugh …
away mrock1t is ::flŒËŒBÈCÔE‘Ï -‘ (see
VIH)
Themaœanumber;
açof
: : aughelonging. ,tÎ0 ths_5sgshers
;
Î Whlchare verycemon
number ofaratheî