A Year at the Shore

by Philip Henry Gosse

THE CROWNED EOLIS.

But we have turned a stone beneath which lurk several specimens of a much lovelier creature yet. I see by the gleams of crimson and azure which shine out from it, that it must be the Crowned Eolis.[18] It looked a little heap of fibrous semi-pellucid flesh when out of water, and, like the Triope, must be immersed to display its beauties. Now in the phial of water, how elegant it is! Its body is long and slender, tapering away to an almost imperceptible point behind, of a clear translucent white. The head forms two long smooth taper tentacles, which wave hither and thither as the creature gracefully glides along; and besides these it has two other tentacles, distinguished as the dorsal pair, resembling, in their position and in their structure, those of the Doris and Triope, but not sheathed.

The chief glory of this exquisite animal, however, is in its breathing organs. These consist of clusters of finger-shaped papillæ, set transversely across the back, in about six rows, with the middle line of the back free. Each of these papillæ is pellucid, with a central core of the richest crimson, while a very brilliant flush of steel blue is reflected from the surface, and the tip is opaque white. The combination of these hues has a most charming effect.

You would scarcely suppose such lovely creatures were fierce and carnivorous; but they are the most determined enemies of the Sea Anemones. This beautiful Eolis I have often seen assaulting an Anemone, ferociously tearing away its tentacles, or gnawing great holes in its side, and, when touched, stiffening and erecting all its brilliant papillæ, as the porcupine does its quills.

All these creatures are Mollusca very closely allied to the Cowry and the Trochus which we lately examined, but destitute of a shell. The exposure of the breathing organs is a distinguishing character (these being more commonly, in the order, concealed in a cavity), whence they are called Nudibranchiata, or Naked-gilled Mollusks.

At this season, wherever we find the animals themselves, we may with confidence expect to find their spawn. This is deposited in masses, which possess characteristic forms. Thus this roll, which looks as if you had made a thin ribbon of paste, half an inch wide, and rolled it into a loose scroll of two or three turns, and then affixed it by its edge to the under side of a stone, is the spawn-mass of the Sea Lemon. And here is a much more elegant scroll, of which the constituent is a slender thread, twisted into a frilled or figure-8 form, as it goes on to make the spire.[19] This has been laid by the beautiful Crowned Eolis. If you examine either of these masses with a lens, you will see that it is composed of a vast multitude of white eggs, suspended in a clear jelly, in which they are arranged in transverse rows, giving the opaque appearance to what would else be colourless and transparent.

EGGS OF NUDIBRANCHS.

The eggs, watched day by day under a good microscopic power, as they advance towards maturity, present a most interesting object of study. The yolk, which at first nearly fills the egg-shell, soon becomes a little elongated, with one end diagonally truncated, or, as it were, cut off obliquely; the truncated end then becomes two-lobed, “each lobe exhibiting an imperfect spiral, and having its margin ciliated. The now animated being is seen to rotate within its prison. Shortly the lobes enlarge, and a fleshy process, the rudimentary foot, is observed to develop itself a little behind them, on the medial line; a shell closely investing the inferior portion of the embryo, the lobes and rudimentary foot being uppermost. The shell rapidly increases, and assumes a nautiloid form; afterwards the foot displays, attached to its posterior surface, a circular operculum, which is opposed to the mouth of the shell. The lobes now expand into two large, flattened, ovate appendages, with very long vibratile cilia around the margins; and the larvæ are at length mature. The whole mass of spawn now presents the utmost animation. Hundreds of these busy atoms are seen, each within its transparent, membranous cell, rotating with great agility and ceaseless perseverance, the cilia all the while vigorously vibrating on the margins of the outstretched lobes. The membranous chorion [or transparent egg-shell], which by this time has become enlarged, ultimately gives way, no longer able to resist the perpetual struggle within; and the liberated larva, wending its way through the shattered shreds of the general envelope, boldly trusts itself to the open trackless water, where, doubtless, thousands and tens of thousands perish ere they find a fitting resting-place, some being swept away by resistless currents, others falling a prey to ever-watchful and innumerable enemies.

“When the larva is at rest, the oral lobes are pulled back into the shell, and the foot being drawn down, brings along with it the operculum, which closes the orifice. But when in action, the whole of these parts project beyond the opening of the shell, the foot lying back against the spire; and the oral lobes inclining forward, their cilia commence to vibrate, and the larva, with the mouth of the shell upwards, moves through the water with lively action, sinking or rising, or advancing onwards at its pleasure.”[20]

SPAWN OF EOLIS.