The Childhood of the Starfish and the
by W. P. Pycraft, F. Z. S., A. L. S.
There are probably not many of my readers who cannot tell a starfish or
a sea-urchin at sight, that is to say, a grown-up starfish or urchin;
but to distinguish between them, or even to recognise them at all, in
the days of their infancy is a very different matter. Indeed, only those
who devote their lives to the study of these creatures are able to do
this, and the facts which their labours have brought to light are
curious indeed, though so complex that it would be impossible to
describe them here in full detail.
Fig. 1.—Young Starfish.
An outline, however, of what we may call the story of the starfish can
be told readily enough, and without in any way losing aught either of
its importance or its interest.
Fig. 2.—Young Starfish, second stage.
Fig. 3.—Young Starfish, third stage.
Briefly, among the starfish people—and including also the sea-urchins
and sea-cucumbers, the curious brittle-stars and feather-stars—parental
care is the exception, and not the rule. Having cast their eggs adrift
upon the sea, the mothers of the families leave the rest to nature. Let
us follow the history of one of these eggs. No sooner is it adrift than
it begins a very remarkable career. Starting at first as a tiny ball, it
divides next into two precisely similar balls, and since these divide
again and again in like manner, we have in a few hours a mass of little
balls, intimately connected with one another, and resembling a mulberry
in appearance, enclosing a hollow space. (Fig. 1.)
This stage reached, the end of the first chapter in the life of the
starfish is closed. He has grown so far, it should be noticed, without
eating; but for further progress food is necessary. Now, this food
cannot be taken in without a mouth and some sort of stomach. These are
formed by the simple device of tucking in one side of the ball, just as
one might push in one side of an indiarubber ball; the rim of the hollow
thus formed becomes the mouth, and the hollow into which it leads is the
stomach, while within the space lying between the outer wall and that
portion of the wall which is pushed in—which corresponds to the inside
of the indiarubber ball—the body that is to be begins to be formed. To
grasp this thoroughly, first of all take such a rubber ball as I have
described, and push in one side. Compare it with the illustration (fig.
Soon after the formation of the mouth, our growing starfish develops his
first organs of locomotion. Now, these are neither arms nor legs, but
take the form of short hair-like growths, endowed with the power of
rapid waving motion, whereby the body is propelled through the water.
These are to be seen in the picture of one of these little creatures,
shown for clearness sake as if cut in half. (Fig. 3.)
Fig. 4.—Nearly full-grown Starfish.
A little later our young starfish has assumed a new shape. Here there is
a large mouth and stomach, while the swimming hairs have all been cast
off except a few arranged in the form of two bands; and, later still,
the creature takes the extraordinary form shown in fig. 4. Swimming by
the motion of waving hairs is now a thing of the past; instead, long
arms have been developed, which perform this work much more effectually,
and these arms are supported by a hard, chalky skeleton. Soon another
little pushing in of the body takes place, and, lo, out of this grows
the body of the starfish that is to be! (as is the middle of fig. 4). In
about forty-five days from the beginning of this eventful history, the
feet and body appear sticking out of the body, whose growth we have been
watching; and, in a very short time after, this chalky skeleton is
destroyed, and the rest of this infantile body cast away, leaving the
fully formed starfish with an entirely new skeleton! Thus, then, wonder
of wonders, this curious creature possesses during its lifetime two
Fig. 5.—Young Sea-urchin.
Fig. 6.-Young Rosy Feather-star.
Fig. 7.—Rosy Feather-star.
The sea-urchin and sea-cucumber undergo similar changes. (See fig. 5.)
So also does the beautiful rosy feather-star, but with certain
modifications too interesting to be passed over. In what we call its
larval body, or its period of childhood, the body takes the form of a
cylinder, as you see in the picture, with a little tuft of swimming
hairs at the bottom, and bands of the same round the body (fig. 6.)
Within this body, as in the starfish, a new body is gradually formed.
Then, as you see in the picture, the inside of the egg-shaped body takes
the form of a long stalk of stony plate, surmounted by a number of
square plates pierced with holes, and these last only are destined to
survive in the body of the adult. Soon after this stage is reached, the
swimming body comes to rest, because the stalked body which it contains
has reached its full development, and takes over the threads of life.
As a consequence, the barrel-shaped swimming body, now useless, is
thrown off, much as a caterpillar throws off its skin, leaving the newly
fashioned body, shaped like a filbert-nut, but rounder, fixed by its
stalk to the ground. In a very little while, however, it puts forth a
number of beautiful moving arms. It is now a sea-lily! And now follows
another change. Breaking away from the traditions of its tribe—the
sea-lilies—it cuts itself off from the stalk, and grows in its place a
number of short finger-like processes, and lo! from a sea-lily it
becomes the rosy feather-star! (What this looks like you can see in fig.
7.) Once more it is able to swim, and this is done by waving movements
of the long arms. When desirous of rest, it drops to the bottom of the
sea, and clutches hold of some bit of rock or branch of seaweed by means
of the bunch of 'fingers' below the body, which we have just described.