Homes Without Hands: Being a Description of the Habitations of Animals, Classed According to Their Principle of Construction

Supposing that the animal is fully expanded, and that the observer has succeeded in placing his eye to the glass without alarming the sensitive creature, he will see a wonderful sight. In its way there is nothing which surpasses in beauty the expanded gill-tuft of a Serpula in perfect health. The long feathery gills radiate from the tube in a curve which combines grace and force in no ordinary degree, while the beautiful colors that glow as the blood courses through their translucent substances are far beyond the power of description.

One use of the gills is evident enough. They serve for respiration. But they also answer another purpose, and aid the animal in procuring food. Being necessarily stationary, it can not roam about in search of food, and its appetite is so great that it would soon die were it to depend for subsistence on the nourishment which might be brought within its reach by the waves.

If a tolerably powerful glass can be brought within the necessary focal distance, it will be seen that the exterior of the gill-tufts is covered with wonderfully delicate filaments, or cilia, as they are technically named, which are continually waving in regular ripples. Their movement constitutes a sharp current of water, which not only washes against the gills and furnishes the requisite supply of air for the regeneration of the blood, but carries the water downward into the mouth, which opens at the bottom of the gill-tufts. In the water is always a bountiful supply of minute animal organisms, together with other substances, which, although microscopically small, are in the aggregate sufficient to feed the Serpula. This current is kept continually flowing as long as the tentacles are protruded, and thus the creature is enabled to breathe, is supplied with nourishment, and the tube is kept clean by the water current which is perpetually rushing through it.

We now come to that wonderful portion of the animal which is called by naturalists the "operculum," and which is popularly and rightly known as the "stopper." This is the conical appendage which hangs from the tube, and is used in closing its mouth when the gills have been withdrawn. The operculum is known to be a development of one of the antennæ, the other antenna being small, slender, and without any such appendage. To systematic naturalists the operculum is one of the most valuable parts of the animal, as it is often found in the tube in good preservation long after all the softer parts of the animal have disappeared. We can learn but little from the tube, as it is very similar in animals belonging to different genera. The value of the operculum was detected by Dr. Philippi, and has been corroborated by Dr. Baird, who has made great use of it in some valuable papers on specimens of Serpulæ which are now in the British Museum.

In one genus, Eupomatus, for instance, the operculum is furnished with a number of movable spikes. In one species, Eupomatus Boltoni, these spikes are about twenty in number, and are hard, flat, and calcareous. Their form is very much like that of a hedger's bill-hook, except that they are furnished on the inner edge with several bold tooth-like projections. These spikes are called by Philippi horns or cornua, and are always deeply toothed, whatever may be the species. The very appropriate name, Eupomatus, is formed from two Greek words, and signifies "beautiful lid," in allusion to the elegant structure of the operculum and its complement of horns.

In another genus, which has been called Placostegus, the operculum is calcareous, flat, and rounded, looking so like the operculum of some aquatic mollusc that it might easily be mistaken for that object. The genus is so named on account of the shape of the operculum, and the word is of Greek derivation, signifying Plate-roofed.

One species of this genus, Placostegus carinatus, is remarkable for a peculiarity which has been brought forward by Dr. Baird, in a paper read before the Linnæan Society in April, 1864. “I wish particularly to bring before the notice of the Society the fact that the animal gives out a beautiful dye or color. The specimens which were the subjects of my examination had been for a number of years in the British Museum, some having been placed there in 1845, and others in 1847. Notwithstanding their having been so long dry, when softened in water, taken out of the tubes and placed in spirits of wine, they imparted to the liquid a beautiful and delicate red tint.”

The specific title of carinatus, or keeled, is given to the animal because its tube has a decided keel or ridge upon its upper surface. The color of the animal is blue, and the fan-like tuft of gills is blue banded with white. An allied species, Placostegus latiligulatus, is remarkable for the shape of its tube, which is defended at the orifice by a kind of pent-house or hood, which projects boldly from the upper edge, just like the peak of a boy’s cap.

Another genus of Serpulæ, called Cymospira, has the operculum horny, elliptical, and furnished with two or more toothed horns, which are generally placed near the hinder edge. Some of the species are very large—one, which is in the British Museum, being as thick as a man’s finger, and being inhabited by a Serpula three inches in length, and more than a quarter of an inch in diameter. Sometimes the horns are long and boldly projecting, and sometimes the tube has a pointed projection like the hood which has already been mentioned. One of the short-horned species which was procured from Swain’s Reefs, on the eastern coast of Australia, was always so imbedded in corals and madrepores that the true shape of its tube can not be ascertained.

Perhaps the most extraordinary example of the operculum is furnished by the genus Pomatostegus, in which the operculum is made in three stories, each smaller than that below it, so that it bears a distant resemblance to the fusee of a watch. In the British Museum is a fine example of this genus (Pomatostegus Bowerbanki), in which the operculum rises like the conventional tower of Babel, all the stories being devoid of horns, but covered with short hairs of a fibrous nature. If the reader should happen to be acquainted with conchology, he can form a very good idea of this remarkable operculum by taking up the similar organ in any species of solarium, or staircase shell, except that in the Serpula the stories of the operculum are distinct, and not formed by successive whorls.

The operculum of the animal which is supposed to be under examination does not present any of these singular appendages, but is more or less conical, grooved above in a radiated form, and horny in substance. It is, however, a very beautiful object, if only for the elegant shape, which remains after the softer parts have perished, and is in form so like a wine-glass with beautifully fluted sides, that Dr. Johnston has remarked that it might serve as a pattern for that article.

THERE is another marine annelid which constructs calcareous tubes, and which is sufficiently interesting to warrant a short notice. If the reader should happen to have in his possession a piece of stone, or an oyster-shell, that has been for some time immersed in the sea, or if he has a piece of the large tangleweed that is so popular as a barometer, he will see that upon the surface are certain tiny calcareous tubes, scarcely thicker than hairs, and rolled spirally so as to form flat circular objects about as large as pins’ heads. They are firmly fixed to the objects on which they are placed, and are often thought to be the earlier forms of the serpula.

These, however, are distinct animals, called Spirorbis by naturalists, who have noticed that their spiral tubes bear a great resemblance to the planorbis shell, which is so plentiful in our rivers and ponds. A tolerably powerful magnifying-glass is needed before the real nature of the Spirorbis can be made out; but a short examination will show that not only is the little worm furnished with gills, or branchiæ which closely resemble those organs in the serpula, but that, like that animal, it can shut up its tube with an operculum of a conical shape.

ANOTHER example of a submarine builder may be found in the well-known TEREBELLA of our coasts, sometimes known by the name of SHELL-BINDER. Sandy shoals are the best spots for the Terebella, and in many places there is scarcely a spare yard of sand without its inhabitants. Like the serpula, the Terebella constructs tubes, but, unlike that animal, it makes the tubes of a soft and flexible texture, although the materials which it employs are far harder than those which are used by the serpula. The Terebella has the art of making its submarine tubes of sand, which it agglutinates together with such wonderful power, that, if Michael Scott’s impish familiar had only been acquainted with natural history, he might soon have learned the art of making ropes of sea-sand, and have turned the tables on his master.

Should any of my readers be desirous of finding the habitation of a Terebella, he may easily do so by repairing to the nearest sandy shore, and looking under every large stone or piece of rock. There he will probably find some loose tufts of sandy threads, which are fixed to the mouth of a flexible tube, made of the same materials. This tube is the habitation of the Terebella, and by means of a crowbar and a chisel the animal may generally be procured, together with its home. There are, however, plenty of deserted tubes, and I have often been sadly disappointed by finding that, after a long and laborious digging, nothing but the empty tube was to be found.

Supposing, however, that a specimen is obtained in an uninjured state, the observer can easily watch its method of house-building by ejecting it from its tubular home, placing it in a vessel filled with sea-water, and supplying it with a handful of sand. As clearness of the water is an essential part of success, shell-sand is the best material that can be supplied, and it will be safer to wash the sand thoroughly before placing it in the vessel. A large rough stone should also be placed in the vessel, as the animal always likes to lurk behind some sheltering object while it is engaged in the task of house-building.

Like many other creatures, the Terebella is a night-worker, and during the hours of daylight will retire behind the stone, and crouch in the darkest corner, as if to repose itself after the violent struggles and gyrations which it enacts when it is first taken out of the tube. Until noon is passed, the only sign of life will be the slight movement of the many tentacles which surround the upper lip; but, as the sun declines, the tentacles begin to move more rapidly, and as if they had some purpose to fulfill. In the evening the worm is in full work; and as Professor Rymer Jones has given a clear and graphic description of its proceedings, I can not do better than transfer his account to these pages. After remarking on the general habits of the creature, and describing the tentacles, he proceeds as follows:

“They,” i. e., the tentacles, “are now spread out from the orifice of the tube like so many slender cords. Each seizes on one or more grains of sand, and drags its burden to the summit of the tube, there to be employed according to the service required. Should any of the tentacula slip, the same organs are again employed to search eagerly for the lost portion of sand, which is again seized and dragged toward its destination.