Evening star. [volume] (Washington, D.C.) 1854-1972, 1892-07-09
MOLLUSKS THAT ARE HERMrTs
Curious Bivalves That Bore Into Solid Rock
and Live There.

and Live There.
WHAT LOOKS LIKE A VERY COMMON
w place lump Of mud has been recently ex-
posed to public view in glass case by itself at
the Smithsonian Institution. Il is much more
Of curiosity than 1t appears at the first glance.
Buried in the mass, which is really drab-colored
limestone, are about dozen molusks that look
somewhat like large 'little neck" or ''long''
clans.
The question naturally occurs. how did these
bivalves find their way into the hard rock, the
openings of the holes they occupy being only a
small fraction Of the size required to admit the
passage OF their bulk. In the case Of q long
clam there is no difficulty in perceiving how it
digs its way down into the sand, leaving behind
1t only little canal through which to commu-
nicate with the outer world. But here the ma
terial bored into is stone. and for long time IL
was mystery even to science how the mollusk
got into the rock, being commonly found where
the latter was between tides'-that is, at times
covered with water and at other times left dry.
1t was like the fly in the amber:
s that that the thing either rich
Happily the puzzle has been solved The
b1valve, which has been named the ''pholas,"
Is originally lodged on the rock in the shape Of
an egg-the accidental survivor OF myriads
lost: May be 1t gets entangled in seaweed, but,
at all events. as sooE as it is Matched out and
appears III Its proper shape as a baby mollusk
1t begins to bore. What it bores with has been
question much discussed. Some have con-
tended that it does the work with the sharp
edges OF its shell, turning round and round for
the purpose; but the material of the shell Is
obviously too soft for that to be possible.
Others have asserted that 1t secretes acids
which eat away the stone, as ichens do in the
vegetable world. But the truth seems to be
that the boring is performed by means of the
foot" Of the animal, with which it patiently
screws hole for ITSELF.
Once lodged in hole Of its own, the little
moliusk has nothing more to fear. But it must
keep on boring all the time, SO as to make more
room for itself as 1t grows. Indeed, inasmuch
as 1t keeps on growing all Of Its life, 1t must al
ways continue to bore. However, 1t has tho
great advantage over nearly all other living
creatures that it resides within an impregnable
house, where no foe can possibly reach 1t. The
hole where 1t entered is never enlarged, and this
hermit among bivalves simply occupies itself in
scooping away the rock as fast as 1t desires more
space. 1t lies some distance, say three or four
inches, from the doorway Of its dwelling filling
up the hallway" az 1t might be termed, with a
sort Of cement secreted by itself, save for a
small passage through which it communicates
with the water or air outside.
When it wants to feed it extends Its long
neck through this passageway and out Of the
aperture, spreading from the extremity of the
organ o number Of delicate tentacles, which
gather in apimalcule and other microscopic
food. In the ordinary course Of nature the
pholas dies, and its decomposed substance is
washed out Of the hole which it occupied while
living. 1t often happens that into the holes
thus left vacant by these bivalves young mol
lusks Of other kinds are conveyed accidentally
by the waves. They grow, and, in 80 doing,
supposing that they belong to species which
attain considerable size. they are compelled to
take the shape Of the holes. Thus concholo-
gists, coming across such tenants in the pholas'
dwellings, used in many instances to mistake
The pholas is very plentiful all along the
Pacific and gulf coasts, and the pretty bival
vular shells are sold in great numbers under
the name of angels wings" on account Of their
peculiar form and markings.