A Year at the Shore

by Philip Henry Gosse

Plate 35.
P. H. GOSSE, del. LEIGHTON, BROS.
BOTRYLLI.

Each bright speck in these radiating star-like systems is an animal essentially of the Ascidian form, with the following peculiarities. All have budded from one primary individual, which was produced as a tiny tadpole, from an egg: the manner and direction in which the buds were put forth determining the starry arrangement. There is a common gelatinous envelope, in which the whole are imbedded, and which ever extends as the individuals and systems multiply, and which seems to have the power of developing isolated individuals which have not budded in the ordinary way, but which then produce others by budding, and so become the commencing points of other systems. In each individual the siphonal orifices are remote from each other, the receiving one being placed on the circumference of the ring or system, while the ejecting one is placed at the opposite end, opening, in common with the discharging siphons of all of that system, into a central main orifice, which rises out of the level with a circular rim, and forms the dark centre of the system.

In the open ocean there are forms of Tunicata which are not attached, but swim freely; and, what is surprising, even compound forms are thus found, progressing by a combined action. One of the most curious is the genus Pyrosoma, which consists of long-bodied Ascidians, so united in rings as to constitute a long, free cylindrical tube, closed at one end and open at the other. By the rhythmical contractions and dilatations of the multitude, this great cylinder slowly swims through the open sea. But the most interesting circumstance in its history is that it is intensely luminous, lighting up the midnight ocean with flashes of vivid light, or seen gliding through the dark water like glowing sticks of fire. So it is described by some voyagers, perhaps with a little exaggeration, for Mr. Bennett, to whom we are indebted for many valuable remarks on oceanic zoology, speaks in more subdued tones of it. His account of this and other pelagic phosphorescence is very interesting:—

PYROSOMA.

“On the 8th of June,” he observes, “being then in lat. 30° S., and long. 27° 5′ W., having fine weather and a fresh south-easterly trade-wind, and the range of the thermometer being from 78° to 84°, late at night, the mate of the watch came and called me to witness a very unusual appearance in the water, which he, on first seeing it, considered to be breakers. On arriving upon deck, this was found to be a very broad and extensive sheet of phosphorescence, extending in a direction from east to west, as far as the eye could reach. The luminosity was confined to the range of animals in this shoal, for there was no similar light in any other direction. I immediately cast the towing-net over the stern of the ship, as we approached nearer the luminous streak, to ascertain the cause of this extraordinary and so limited phenomenon. The ship soon cleaved through the brilliant mass, from which, by the disturbance, strong flashes of light were emitted; and the shoal, judging from the time the vessel took in passing through the mass, may have been a mile in breadth. The passage of the vessel through them increased the light around to a far stronger degree, illuminating the ship. On taking in the towing-net, it was found half filled with Pyrosoma (Atlanticum?), which shone with a beautiful pale-greenish light; and there were also a few shell-fish in the net at the same time. After the mass had been passed through, the light was still seen astern, until it became invisible in the distance; and the whole of the ocean then became hidden in the darkness as before this took place. The scene was as novel as beautiful and interesting; more so from my having ascertained, by capturing luminous animals, the cause of the phenomenon.

“The second occasion of my meeting these creatures was not exactly similar to the preceding; but though also limited, was curious, as occurring in a high latitude, during the winter season. It was on the 19th of August, the weather dark and gloomy, with light breezes from north-north-east, in lat. 40° 30′ S., and long. 138° 3′ E., being then distant about 368 miles from King’s Island (at the western entrance of Bass’s Straits). It was about eight o’clock P.M. when the ship’s wake was perceived to be luminous; and scintillations of the same light were also abundant around. As this was unusual, and had not been seen before, and it occasionally, also, appeared in larger and smaller detached masses, giving out a high degree of brilliancy, to ascertain the cause, so unusual in high latitudes during the winter season, I threw the towing-net overboard, and in twenty minutes succeeded in capturing several Pyrosomata, giving out their usual pale-green light; and it was, no doubt, detached groups of these animals that were the occasion of the light in question. The beautiful light given out by these molluscous animals soon ceased to be seen emitted from every part of their bodies; but by moving them about it could be reproduced for some length of time after. As long as the luminosity of the ocean was visible (which continued most part of the night), a number of Pyrosoma Atlanticum, two species of Phyllosoma, an animal apparently allied to Leptocephalus, as well as several crustaceous animals (all of which I had before considered as intertropical species), were caught and preserved. At half-past ten P.M. the temperature of the atmosphere on deck was 52°, and that of the water 51½°. The luminosity of the water gradually decreased during the night, and towards morning was no longer seen, nor on any subsequent night.”[156]

SPONGES.

Let us come back from the wide world of waters, with its nightly illuminations, and its other ten thousand marvels, to our own homely and quiet beach. A tribe of existences is awaiting our notice, which we have as yet neglected; which yet we cannot fail to observe whenever we peep beneath these boulders, and look at these rocky ledges, just left exposed by the lowest retiring tides. They are the Sponges; the most debateable forms of life, long denied a right to stand in the animal ranks at all, and even still admitted there doubtingly and grudgingly by some excellent naturalists. Yet such they certainly are, established beyond reasonable controversy as true and proper examples of animal life, and therefore having a rightful claim to be painted and described in this series of essays. However, as they are the lowest, so shall they be the last; for, with a few notes on some of our species, I shall dismiss my kind and courteous readers.

The inferior surface of this huge slab of limestone, supported at one end by a boulder, while the other end is imbedded in the mud or concealed by the smaller fragments that are thrown in confusion around, is densely studded with organisms. It is only at very low tides that this arch is exposed, though now we can creep in and work with no great discomfort, though with some defilement of our garments from the mud and slime. The absence of direct light is favourable to the growth of marine productions, and thus we have another congenial element in the obscurity. With some of the smaller sea-weeds, chiefly of the filamentous kinds, as Cladophora, Conferva, some of the minuter Callithamnia, etc., the majority of the forms that crowd and cover the rock so densely are animals: indeed there are large areas where the animate forms struggle so perseveringly for standing-room, that not a filament or frond of vegetation can be seen, and you could not thrust the point of a penknife down to the rock in any spot without wounding some or other of the incrusting creatures. Polyzoa are here, chiefly of the tufted species; Hydrozoa, too, hang down; Anemones, but not in abundance, may be seen; Saxicavæ push their crimson siphons through, here and there; Botrylli are spread in patches, and Amœrœcia are suspended like a plentiful crop of tempting strawberries; but Sponges constitute the staple of the crop; it is a veritable field of Sponge.