20
THE SEASJ
—
'
tubes of lime, sand 0'r parchment—like material which they '
make for themselves, enlarging them as they grow and being
in many cases able to make new Ones if they are destroyed.
CloSely related are the leeches of“ which there are -marine
species which suck the blood of sh, and rather less so the
‘
Sipunculids which'have'a protrusible prob_oscis and a tough
leathery* body without any sign of segmentation.
They
are
all marine.
One of the commonest constituents of
the driftirig life of the sea is the little arrow worm, Sagitta,
'
which belongsto a small group called the CHÆTOGNATHA,
whiCh has no connection with the other worms.
‘
Quite closely related to the bristle—worms are the POLYZOA
Or sea mats, minute‘ créatures which always live in colonies,
-
someof ”which are small and branching likethe hydroids,
and others large and with strong limy skeletons which give
them the appearance of delicate corals.
In spite of their
.
minute size the individual animals arevery Complex.
.
—
The ECHINODERMATA_ are a diverse group, exclusivelymarine, which include the starsh and seaurchin.
'
Like
_
the Cœlenterates, they are built On a radial plan though,
'
-
oWing to their mode of life;sQm‘e have altered this and-become
bilaterally symmetrical.
They call have limy skeletons,
some
consisting of continuous plates forming a compact
shell as in the sea urchins, and others of isolated spicules
or tubercles embedded in a leathery skin, as in the seacucumbers.
They are in most instances either attached
.
orwvery' slowly—moving animals, the mechanism of loco—
motion being usually provided by the peculiar
“
tube.
feet,” tiny tubes which are worked by water power supplied
by a series of canals within the
There
ve
distinct groups, the starsh (Asteroidea) with a— at central
disc to which are attached a number of arms, usually ve,
.
tho'ugh itmay be many more; the brittlestars '(Ophiuf—
.
_
oidea) ”n‘ot— unlike the îstarsh=but “with the disc more
THE SEASJ
—
'
tubes of lime, sand 0'r parchment—like material which they '
make for themselves, enlarging them as they grow and being
in many cases able to make new Ones if they are destroyed.
CloSely related are the leeches of“ which there are -marine
species which suck the blood of sh, and rather less so the
‘
Sipunculids which'have'a protrusible prob_oscis and a tough
leathery* body without any sign of segmentation.
They
are
all marine.
One of the commonest constituents of
the driftirig life of the sea is the little arrow worm, Sagitta,
'
which belongsto a small group called the CHÆTOGNATHA,
whiCh has no connection with the other worms.
‘
Quite closely related to the bristle—worms are the POLYZOA
Or sea mats, minute‘ créatures which always live in colonies,
-
someof ”which are small and branching likethe hydroids,
and others large and with strong limy skeletons which give
them the appearance of delicate corals.
In spite of their
.
minute size the individual animals arevery Complex.
.
—
The ECHINODERMATA_ are a diverse group, exclusivelymarine, which include the starsh and seaurchin.
'
Like
_
the Cœlenterates, they are built On a radial plan though,
'
-
oWing to their mode of life;sQm‘e have altered this and-become
bilaterally symmetrical.
They call have limy skeletons,
some
consisting of continuous plates forming a compact
shell as in the sea urchins, and others of isolated spicules
or tubercles embedded in a leathery skin, as in the seacucumbers.
They are in most instances either attached
.
orwvery' slowly—moving animals, the mechanism of loco—
motion being usually provided by the peculiar
“
tube.
feet,” tiny tubes which are worked by water power supplied
by a series of canals within the
There
ve
distinct groups, the starsh (Asteroidea) with a— at central
disc to which are attached a number of arms, usually ve,
.
tho'ugh itmay be many more; the brittlestars '(Ophiuf—
.
_
oidea) ”n‘ot— unlike the îstarsh=but “with the disc more