This little Sucker is easily reconciled to captivity. I have in my
aquariums some individuals which were captured nearly a year and a
half ago; and they are still in the full enjoyment of health and
activity. They are pleasing little things: they scuttle from spot to
spot with a spasmodic sort of bustle, wagging their tails much from
time to time, so that in movement as well as in form they remind one
of tadpoles. They are generally seen, however, anchored to the sides
of the vessel, or to the prominent knobs of the stones by their
sucker, and here they remain for an indefinite time, sometimes for
hours, at others only a few seconds, throwing their beautiful eyes
about in insatiable curiosity, fanning the water with their transparent
pectorals, or whisking the painted tail about. Now and then they make
a sudden snap, doubtless at some passing animalcule, with an audible
sound, and the emergence of a bubble of air from the top of the water,
whence the muzzle is frequently projected. They have an awkward habit
of throwing themselves out of a shallow vessel; and if you are not on
your guard you may find your little pets dead and dry on the carpet.
They are inquisitive little things; if a new stone or shell or tuft of
serpulæ is put into their vessel they soon discover it, and may be seen
exploring it in every part; and it is amusing, when _you_ are examining
_them_ with a lens, to note how thoroughly mutual is the investigation;
for you can see by the direction and motion of the eyes that the little
fish is watching you as interestedly as you are observing him.
I do not think that the adhesion of the ventral sucker is effected
exactly as has been supposed, by a vacuum produced in the area of
the united ventral fins; but by the combined action of some minute
fleshy sucking disks, which are arranged in two groups, in front of
and behind the united fins. The conjoined fins do not appear to me to
make a vacuum. The fish has a curious habit of coming to the surface
of the water, and there floating perfectly still, back downward, the
entire belly-surface dry. The ventral disk is then seen as a shallow
cup, quite dry and shining. If touched, the little fish hurries along
the surface, with some splashing, till it acquires impetus enough
to go under at an oblique angle, when it presently turns over, and
adheres to the bottom, or side of some stone. I have seen this practice
frequently, but only, I think, at night.[87]
* * * * *
This principle of a vacuum produced by the retraction of the centre
of a fleshy disk, while the margins remain in close contact with a
solid body, is of extensive application in the lower forms of animal
life, and especially in the class ECHINODERMATA, comprising what are
popularly known as Star-fishes, Sea-urchins, and Sea-cucumbers.
I have on other occasions noticed the elaborate and wonderful mechanism
of the sucker-feet as they appear in the commoner species of the class.
I need not therefore repeat those details, but look at a few other
particulars in the economy of the animals whose locomotion is dependent
on this curious contrivance.
There is a pretty little species abundant enough hereabout, chiefly
affecting shores on which numerous angular masses of stone lie
irregularly scattered and heaped one on another. Yet they seem to have
a predilection, for they do not occur in all our localities even though
these conditions be not lacking. Livermead Point, and the south side of
Anstey’s Cove, beneath the cliffs, are favourite spots for them, the
former especially, where we can find the little Gibbous Starlet,[88]
for such is its name, at all times of the year, when the tide is
sufficiently out. The retiring tide here leaves a shallow pool of
considerable area, which then continues to run out by a narrow channel
among the rock boulders, a winding rivulet of salt water; along whose
borders, by turning over the loose blocks, scores of this pretty Star
are exposed, clinging to the wet sides and roofs of the dark passages
by means of their sucker-feet. Forbes has given two figures of the
species, but manifestly taken from dead specimens, and from very small
ones too. He says, “large specimens measure only an inch across;”
from which I infer that on the shores of the Isle of Man, where he
was familiar with it, the Starlet does not attain the dimensions it
reaches on our mild southern coast. He indeed alludes to one in Mr.
Ball’s collection, which measured one inch and five lines in diameter.
Specimens, however, of this size are quite common with us, nor would
one of an inch and a half be looked upon as at all exceeding the modest
and proper range of the species.
[Illustration: