The “compound Zoöphytes,” or, more properly, Polyps, as being, as it were, many creatures in one, are still more curious than the two classes just described. A common example of this class is the Alyconium digitatum, looking like a mass of short fingers, when the final florets are closed, as its specific name imports, being sometimes called, by the fishermen of our northern coasts, Dead-men’s-toes. Each finger-like cell contains a separate creature, whose tentacles, when expanded, form the floret, after the manner of those of the Sea-Anemonies, but yet each separate creature is vitally attached to a central polypidom, or spine, which binds the whole group into one existence.
Of this class are the curious Pennatulidæ, one of which is commonly known as the Sea-Pen. The three species of this class of Polyps known to inhabit the British seas, are so distinct from each other that they form at the same time three distinct genera. The most beautiful of the three is the Pennatula phosphorea, the Sea-Pen, which is not uncommon on some parts of our northern coasts. It is represented in [Plate VII.] The purple branches, or pinnæ, of the upper portion, form the feathered part of the quill pen to which it is likened; the bare portion of the polypidom below having certainly some resemblance to the quill. This curious zoöphytic form is often seen in an erect position, planted, as it were, in the mud like a miniature purple Pine, though it is capable of motion through the water from place to place, by some action of its organs which has not been accurately detected. It is one of the handsomest of our British Zoöphytes. The polypidom, or trunk, is three or four inches long, fleshy, and of a purplish red. It is naked at the lower end, and feathered above with long, closely-set pinnæ, along the margins of which the polyp-cells are placed. The pinnæ are curved backward, and capable of either separate or united motion. They are supposed by some to be capable of the action of regular oars; but this is very doubtful, though their bearing on the polypidom, which is strengthened by an internal column of calcareous or bony matter, would give them considerable power for that purpose. The creature’s specific name, phosphorea, must not lead to the supposition that it always emits a phosphorescent light, for it is only when irritated that this is produced. If plunged into fresh-water, it scatters a shower of phosphoric sparks in all directions, which forms a magnificent and curious spectacle, far more brilliant, no doubt, than the fabled hues of the dying dolphin.
The Virgularia mirabilis is another of this class of creatures, almost as elegant as the Sea-Pen, but more slender, and in the form of a branching rod, as its name imports. (See [Plate VIII.])
The Sponges form a curious class of Zoöphytes, which have perhaps a much closer affinity to plants than any other. They are occasionally very sportive, and curious in their forms; and Dr. Johnston enumerates fifty-six species belonging to our coasts; they are, however, unsuited to the Aquarium in the present state of our knowledge; and when portions of rock are collected on the shore, for the tank, care should be taken to clear off any Sponge formations that are perceived, as their certain and rapid decay would be liable to injure the condition of the whole colony of the Aquarium.
CHAPTER VI.
THE MOLLUSCS, ETC.
The curious floral forms of the Zoöphytes have, as yet, attracted the greatest degree of attention among the constructors of marine Aquaria; yet other forms of ocean life offer equal, if not superior, opportunities for curious observation, and are equally well calculated to bear the confinement of the tank. Among them all, none more than the Molluscs, especially the shell-bearing division, which merits the careful attention of the student of Nature, as forming some of her most singular manifestations.
The knowledge of the nature and structure of many of the most curious shell-bearing Molluscs is of very recent date, with the exception of those which possess obvious qualities which have fitted them for articles of diet or commerce; such as the Oyster, Mussel, Cockle, &c., as eatable species—and the Purples, Sepias, and Cuttle-fish, as containing valuable dyes. With the exception of such as these, the pearl-yielding Bivalves, and a few others, nothing was known, with a few remarkable exceptions, of the animals that create and inhabit the beautiful shells that have so long been ranked among the most elegant objects of the cabinets of the curious. Many of these were, in fact, scientifically classified by learned naturalists before the nature of the animal, of which they formed the mere senseless husk, was even guessed at. The ordinary collector did not even desire to know anything of the creature which produced the shell he most prized; it was sufficient for him that it was estimated as “rare” by his brother collectors—rarity being a quality more highly prized than even beauty. With this feeling, prices as great were given for single shells as ever enthusiastic Hollander paid for a coveted bulb during the height of the Tulipomania. No amount of guineas was too much, at a sale of shells, for such a contested prize as a Many-ribbed harp, a Gloria maris, a Cedo nulli, or a Voluta Junonia. But that race of idle shell-fanciers has given place to a race of true conchologists, who are investigators as well as collectors, and whose labours are daily developing unexpected and valuable knowledge from those long obscure pages of the great book of Nature.
The marine Aquarium may be made the means of many curious discoveries regarding the habits and organization of the shell-bearing Molluscs; and, with this feeling, I may direct the attention to several of their singular characteristics, in order that they may serve as clues to the detection of others.