All of us who enjoy looking in coastal rock pools are
pleased when we find a starfish sheltering under a stone, or under fronds of
algae. When we pick up our specimen, we see that the undersides of its arms bear
many tube feet that are used both in locomotion and also as a means of
obtaining food. Their use is explained in the following video clip [1]:
In the Nineteenth Century, our knowledge of starfish locomotion
was dependent on written accounts, aided by illustrations, and no-one was
better at describing the animals of the shore than Philip Henry Gosse. In Land
and Sea, Gosse writes of a visit to Meadfoot Beach in Torquay to explore
the rock pools there (see below), a collecting site within easy walking
distance of his home [2].
Gosse found a large starfish in the Meadfoot rock pools and moved
it to another pool that provided a better chance of detailed study, as the
animal was too large to take back to his aquarium. His description in Land
and Sea [2] of its locomotion provides an interesting comparison with the
video recording above. In reading it, we can admire Henry Gosse’s ability as a
writer and it is easy to see how he was such an important figure in the
development of the “Marine Biology Craze” of the Victorian era:
I mark it gliding smoothly, and
with a moderate rapidity, over the unevenness of the rocky bottom, and notice
the mechanism by which its progression is effected, I see at once that I have
before me one of the great types of animal locomotion; a series of contrivances,
by which a given end, that of voluntary change of place, is accomplished, which
are quite sui generis; admirable in their adaptation to the prescribed
end, but totally unlike the arrangements by which the same object is attained
in higher forms of life..
..Each of the five thick and
bluntly-pointed arms, or rays, of this star-like animal is seen to be indented on
its underside by a rather wide and deep furrow, which extends from the hollow
in the centre, where the mouth is seated, throughout its length, to the point.
Along the floor of this groove we should see in the dead and dried animal four
rows of minute perforations, running lengthwise. We cannot discern them
directly during the living activity of the starfish, because the crowding
sucker-feet conceal them. Each of these suckers is a tube of delicate membrane,
a continuation of the common skin; and its interior accurately corresponds with
one of these perforations in the skeleton..
..If we were to dissect this
animal, we should find, on the interior surface of the semi-crustaceous
integument of the arm, a little globular bag of similar transparent membrane, on
each aperture, which opens into the cavity of the globe, just as on the outer
side it opens into the tube. Thus there is a free intercommunication between
the globose sac on the inside and the sucker-tube on the outside, through the
tiny perforation in the crust. The interior is filled with a clear fluid,
scarcely differing in its nature from sea-water. The globular sac within and
the tube without are both composed of highly contractile tissue, under the
control of the animal will.
Gosse goes on to describe the stepping motion of the tube
feet, but does not describe the complete water vascular system, its connection
to the surrounding sea water via the madreporite (the porous plate shown in the
video), or the nervous system by which the movement of the tube feet is controlled.
Being a devout Christian, he does, however, state:
Here we have one of the
multitudinous results of the infinite Wisdom and almighty Power combined in
creation. The problem is to endow with the faculty of voluntary locomotion a sentient
creature which has no internal skeleton, and no limbs. It is solved in many
ways in the invertebrate classes, and this is one example.
While writing this, Gosse was aware that there was a growing
acceptance of the theory of evolution (Darwin having published On the Origin of
Species in 1859), something which he vehemently opposed, as he believed in a
literal interpretation of the story of Creation in the Book of Genesis. He looked
upon the wonderful complexities of the natural world as the work of an
all-powerful God.
I, too, am filled with amazement when looking at specimens
of the same animals and plants that Gosse observed and this always presents a
challenge. Coming back to the example of locomotion in starfish, I find myself trying
to answer questions on how the water vascular system evolved – what were the
various stages required and did they occur near-simultaneously, or gradually? Isn't the sense of wonder posed by such questions very similar to that Gosse
felt about God's Creation?
[2] Philip Henry Gosse (1865) Land and Sea. London,
James Nisbet & Co..
