42
'
.
CTI—IE SEAS_
surface of the shell of sea urchins are little clawed spines,
Û,Ï
of various patterns, but usually with three teeth which
can open and snap together.
These are used to clean the
.
shell, removiîng any fragment of waste matter, but also for
protection, for if an enemy attacks an urchin the long spines
on that side turn away exposing the smaller clawed spines
beneath‘, which snap at any part of the enemy touching
them”, and also produce a poison which _p'asses into the
Wound.
’
'
..More universal are methods of passive defence.
The
thick shell. of the crustaceans and of the uniValve ' and
bivalve - molluscs are
examples.
The
last—named
are
frequently “safe so long as their shell can be rmly closed and
the two muscles concerned with this—the’adductor muscles
of the shell—are extremelypowerful, though very variably
so in different 'beas c's,"th‘o‘Se of the cockle for example having
less than ‘a quarter the power of those of Venus.
How the
,
.
'
bivalves maybesuccessfully attacked and eaten by whelks
_
and starsh we shall see in Chapter IX.
The hermit crabs
‘
have found an excellent means of protection by using
empty mollusc shells.
Then there are the various devices '
an animal escapes attention by toing with the
.
,
background.
This may” be done by having a colour similar
to the surroundings—one — particular set of surtoundings
.
or any surroundings, the animal—in the latter case changing
.
its colour to tone with the background.
This is particularly
Ï
Common in small crustaceans and at-sh on the shore.
The vivid colours of “many sea slugs, which are unable,
however, to change colour, usually tone with those of the
rocks or weed on which -' they
Many spider crabs
-
“
mask ” themselves by delibera—tely decking their shells ‘ '
With pieces
weed or sponge which continue to grow
'
there.
-The dahlia anemone and the smaller sea Curchin
-
f
both cover
themselves .with stones and pieces of shell
'
.
CTI—IE SEAS_
surface of the shell of sea urchins are little clawed spines,
Û,Ï
of various patterns, but usually with three teeth which
can open and snap together.
These are used to clean the
.
shell, removiîng any fragment of waste matter, but also for
protection, for if an enemy attacks an urchin the long spines
on that side turn away exposing the smaller clawed spines
beneath‘, which snap at any part of the enemy touching
them”, and also produce a poison which _p'asses into the
Wound.
’
'
..More universal are methods of passive defence.
The
thick shell. of the crustaceans and of the uniValve ' and
bivalve - molluscs are
examples.
The
last—named
are
frequently “safe so long as their shell can be rmly closed and
the two muscles concerned with this—the’adductor muscles
of the shell—are extremelypowerful, though very variably
so in different 'beas c's,"th‘o‘Se of the cockle for example having
less than ‘a quarter the power of those of Venus.
How the
,
.
'
bivalves maybesuccessfully attacked and eaten by whelks
_
and starsh we shall see in Chapter IX.
The hermit crabs
‘
have found an excellent means of protection by using
empty mollusc shells.
Then there are the various devices '
an animal escapes attention by toing with the
.
,
background.
This may” be done by having a colour similar
to the surroundings—one — particular set of surtoundings
.
or any surroundings, the animal—in the latter case changing
.
its colour to tone with the background.
This is particularly
Ï
Common in small crustaceans and at-sh on the shore.
The vivid colours of “many sea slugs, which are unable,
however, to change colour, usually tone with those of the
rocks or weed on which -' they
Many spider crabs
-
“
mask ” themselves by delibera—tely decking their shells ‘ '
With pieces
weed or sponge which continue to grow
'
there.
-The dahlia anemone and the smaller sea Curchin
-
f
both cover
themselves .with stones and pieces of shell