Fig. 118.—The Sea Mouse
The Sea Mouse (Aphrodita aculeata) is certainly one of the most interesting of the roving marine worms, and, though seldom seen above low-water line, may often be obtained by the sea-side collector with the aid of friendly fishermen, who sometimes find it plentifully among the contents of their trawl nets. Failing such aid, it may be looked for among the encrusted stones that are exposed only at the lowest spring tides, especially in places where a certain amount of mud has been deposited under the shelter of outlying rocks; and the chances of success are much greater if the search is made immediately after a storm, for at such times much of the life that exists in deep water will have been driven shoreward by the force of the waves.
At first sight the sea mouse would hardly be associated with the worms; for, instead of having the elongated and cylindrical form that is usually regarded as characteristic of these creatures, it is broad and slug-like in shape, the under surface, on which it crawls, being flat, while the upper side is convex. The segmentation of the body, too, is not readily seen in the upper surface on account of the thick felt-like covering of hairs, but is at once apparent when the creature has been turned over to expose the ventral side.
When seen for the first time in its natural haunt one naturally wonders what the moving mass may be. Crawling sluggishly over incrusted stones, or remaining perfectly still in a muddy puddle that has been exposed by overturning a stone, it looks like a little mound of mud itself, about four or five inches long, and its general colour and surface so closely resembles that of its surroundings that an inexperienced collector may never even suspect that the mass is a living animal form. But take the creature and wash it in the nearest rock pool, and it will be recognised as a broad segmental worm, thickly covered with fine hairs above, and its sides adorned by bristles that display a most beautiful iridescence. It is not easy to see the value of this gorgeous colouring to the animal, and it is doubtful whether, on account of the muddy nature of the creature’s home, such colouring is often displayed to the view of other inhabitants of the sea; but it is well known, on the other hand, that sea mice are readily devoured by fishes, even though they possess an armature of stiff and sharp spines, and that they must therefore be often preserved from destruction by the close resemblance of the general colour to that of their surroundings.
The gills of the sea mouse are not prominent appendages, as with most marine worms, but are soft fleshy structures situated beneath the overlapping scales that lie hidden below the thick hair of the upper surface.
As it is most probable that the reader may desire to preserve a sea mouse at some time or other, a few words concerning the best methods of doing this may be of value. If it is to be preserved in fluid, it should be thoroughly washed to remove all the mud that normally covers its body, and then placed in spirit or formaldehyde, both of which fluids have no destructive effects on the iridescent colouring of the bristles. If, however, it is desired to keep the specimen in a dry state, it should first be put into strong spirit containing a few grains of corrosive sublimate, for a few days. It should then be put under considerable pressure between several thicknesses of absorbent paper to expel the fluid it contains, as well as all the softer internal structures. By this means it will have been squeezed quite flat, so that it presents anything but a natural appearance; but the skin may be blown out to the normal shape by means of a glass tube inserted into the mouth, and then set aside to dry. As the water it originally contained has been extracted by the strong spirit, the drying takes place very quickly; and the small amount of corrosive sublimate that has penetrated into its substance will be sufficient to protect it from the invasion of those pests that commonly attack our museum specimens.
Passing now to the sedentary or fixed worms, we meet with some that are very interesting and beautiful creatures, even when considered apart from the wonderful homes they construct. The several species of the genus Terebella form a soft and flexible tube by binding together particles of sand, shells, or mud with a sticky substance that exudes from their own bodies. These tubes are to be found in abundance between the tide-marks on almost every low, sandy shore, the nature of the tubes varying, of course, with the character of the materials at the disposal of the builder.
In some cases the tubes are exposed throughout the greater part of their length, but very frequently they are more or less buried in the sand or other material of the beach, so that one has to dig to a moderate depth in order to extricate them. In either case, however, the tube of Terebella may be known by the free tufts of sandy threads that form a deep fringe around its mouth.