Actiniaria

“ The wonderful colours of our British Sea-anemones are familiar to most persons who have visited the sea-side. The common Actinia mesembryanthemum of rock pools, for example, is of a purple red colour. The base is usually green with an azure line. Around the margin of the disc there are some twenty-five turquoise blue tubercles. On each side of the mouth there is a small purple spot, and the numerous tentacles forming a circlet round the mouth are of a pale roseate colour. Nothing could be more beautiful than the snowy-white Actinoloba dianthus or the variegated Urticina crassicornis. ”

“ Strange to say, the Actiniæ, which live in the mud, are among the most beautifully colored of these animals. They frequently prepare their home with some care, lining their hole by means of the same secretions which give their slimy surface to our common Actiniæ, and thus forming a sort of tube, into which they retire when alarmed. But if undisturbed, they may be seen at the open door of their house with their many colored disk and mottled tentacles extending beyond the aperture, and their mouth wide open, waiting for what the tide may bring them. ”

“ Actinia Dianthus.—This is the Plumose anemone of Mr. Grosse, and sometimes bears the very appropriate name of the Carnation anemone. It is the most superb of our native Actinias—a gorgeous creature, that in itself more than realizes our brightest imaginings of the hidden splendours of the ocean floor, and of the gems that bedeck the caves of Neptune. How will future poetry be affected by the revelations of the aquarium, and how far will the sober facts of scientific research influence the pictures and the incidents of romance? ”

“ The Actinia are at once gluttonous and voracious. They seize their food with the help of the tentacula, and engulf in their stomach, as we have seen, substances of a volume and consistence which contrast strangely with their dimensions and softness. In less than an hour, M. Hollard observed that one of these creatures voided [187] the shell of a mussel, and disposed of a crab all to its hardest parts; nor was it slow to reject these hard parts, by turning its stomach inside out, as one might turn out one's pocket, in order to empty it of its contents. ”

“ As to the time, and even the method of propagation, mother actinia is very capricious, there being, so far as our observations may determine, no regularity, but at the right time doubtless, for her convenience, the actinia evicts her young. Usually these are discharged at the mouth. They are tiny little things, clad with cilia, with which they move freely in the water for a little while, then settle on some stone, and give themselves up to a sedateness worthy the parent that gave them birth. It often happens that mother Anemone sends out her little ones in a very rough way into the world. ”

“ But actinias have been known to exert great muscular power, and show high possibilities of recuperation. Thus Dr Johnson, of Berwick, saw one whose skin had been cut through by a shell fish it had swallowed, but which outgrew the injury. Then Mr C. Peach has observed actinias spurt out periwinkles, limpets, &c. from their central stomach when they had assimilated the fleshy contents. May not, then, our actinia have come to a premature death through its living for sixty years in civilisation? What brief lives domestic animals have compared with their savage kindreds! ”

“ It is a very pretty and hardy object in the aquarium. There are many varieties, some of which are very delicate, as the Actinia anguicoma, or Snaky-locked Anemone, and the pink and brown Actinia bellis, which so resembles a daisy. Others, as the Actinia parasitica, are obtainable only by deep-sea dredging; "and, as its name implies, it usually inhabits the shell of some defunct mollusk. And more curious still, in the same shell we usually find a pretty crab, who acts as porter to the anemone. ”

“ The connection between Brainstones, Mushroom Corals, and other Madrepores abounding on Polynesian reefs, and the “Sea Anemones,” which have lately become so familiar to us all, can be seen by comparing our comparatively insignificant C. Smithii with our commonest species of Actinia and Sagartia. The former is a beautiful object when the fleshy part and tentacles are wholly or partially expanded. Like Actinia, it has a membranous covering, a simple sac-like stomach, a central mouth, a disk surrounded by contractile and adhesive tentacles. ”

“ Taken in the hand, the sea-anemone imparts a slippery feeling, and it seems to have the consistency of leather. To get at its precise form, look at the cut given of Actinia rosea, a British species. Now, please follow closely our description a little while. As the actinia erects itself, attached to a rock or stone, it looks like one of the purses formerly fashionable, if one such could be made to stand of itself erect, and have the frill around the upper end to project in a circle. ”

“ Generally, however, it is found embracing some univalve shell, which is tenanted by a Soldier Crab; young specimens on Turritella terebra, Trochus magus, T. ziziphinus, &c., but adults, which are much more frequently met with than the young, almost invariably on the great Whelk (Buccinum undatum) . The dredge indeed often brings up shells invested by the Actinia which are empty; but I believe that in every such case, the shell has recently been vacated by the soldier, and that the Actinia never voluntarily selects an empty shell for his base. ”

“ The Bicidium (Fig. 14) , our parasitic Actinia, is to be sought for in the mouth-folds of the Cyanea, our common large red Jelly-fish. In any moderate-sized specimen of the latter from twelve to eighteen inches in diameter, we shall be sure to find one or more of these parasites, hidden away among the numerous folds of the mouth. The body is long and tapering, having an aperture in the extremity, the whole animal being like an elongated cone, strongly ribbed from apex to base. At the base, viz. at the month end, are a few short, stout tentacles. ”

“ The mouth of the Actinia opens among the tentacles. Oval in form, it communicates by means of a tube with a stomach, broad and short, which descends vertically, and abuts by a large opening on the visceral cavity, the interior of which is divided into little cells or chambers. These cells and chambers are not all of the same dimensions; in parting from the cylindrical walls of the body, they advance, the one increasing, the others getting smaller, in the direction of the centre. ”

“ These threads, called acontia, are thickly beset with stinging-cells, which must at least cause a violent smarting on the soft skin of the octopus. Thus we see that the Actinia instinctively defends its partner from attacks, and does it so effectively that we need not wonder how the instinct to provide itself with Actiniæ could have arisen in the hermit-crab. ”

“ How often they eat when free in their natural element is unknown, but weekly feeding is said to be sufficient to sustain them in an aquarium. Small bits of meat are acceptable food, which can be dropped into the water. The instant a descending morsel touches the petals, or tentacles, of a hungry anemone, it is eagerly seized and drawn into the open, greedy mouth. The Actinia mesembryanthemum is a very long-lived creature, and certain specimens are reported to have lived over twenty years in aquaria in England. ”

“ When irritated, the creature has the power of attaching the tentacles to the object which annoys it, and in this way it frequently clings to the fingers when handled, and at the same time squirts out numerous jets of water, until it is quite empty and collapsed.
Actinia Parasitica.—This is a good aquarium species, on account of the ease with which it may be kept. It is a species that the rambler on the sea-beach will not be at all likely to meet with, for it is truly pelagic in its habit. ”

“ In the rude and blundering manner in which the bearer performs his office, it cannot be but that the poor Actinia gets many a hard knock, and many a rough squeeze, among the rocks and stones over which his servant travels; but he appears to bear these mischances with great philosophy: I know of no species which lives so constantly expanded. A rude shock will indeed cause it to withdraw its tentacles, and contract its disk into that button-like shape which is common to the genus ”

“ As far as the anatomy of the zooid is concerned, the majority of the stony or madreporarian corals agree exactly with the soft-bodied Actinians, such as Actinia equina, both in the number and arrangement of the adult mesenteries and in the order of development of the first cycle. The few exceptions will be dealt with later, but it may be stated here that even in these the first cycle of six couples of mesenteries is always formed, and in all the cases which have been examined the course of development described above is followed. ”

“ It has been repeatedly observed that an actinia has a stinging, or, as it is called, an urticating power over the tissue of other animals. Now, there are in different parts of the body of an actinia innumerable cells, from which, especially the cells on the tentacles, it can dart an invisible thread. ”

“ Phylogeny of the Acantharia.—The legion Acantharia or Actipylea is distinguished by its peculiar acanthin skeleton, which develops centrogenously, as well as by the disposition in groups of the pores in its central capsule, and its excentric usually precocious nucleus; it is thus so different from all other Radiolaria as undoubtedly to furnish, phylogenetically considered, an independent stem (§ 7) . This stem is only connected at the root by Actinelius with the primitive form of the Spumellaria, Actissa. ”

“ The class of Polyps is divided into three orders,—the Halcyonoids, the Madreporians, and the Actinoids. Of the lowest among these orders, the Actinoid Polyps, our Actinia or sea-anemone is a good example. They remain soft through life, having a great number of partitions and consequently a great number of tentacles, since there is a tentacle corresponding to every chamber. Indeed, in this order the multiplication of tentacles and partitions is indefinite, increasing during the whole life of the animal with its growth ”

“ The archenteron becomes the gastrovascular system or coelenteron. Between the ectoderm and endoderm a gelatinous supporting layer, termed the mesogloea, makes its appearance. The gastrula has now become an actinula, which may be termed the distinctive larva of the Cnidaria, and doubtless represents in a transitory manner the common ancestor of the group. In no case known, however, does the actinula become the adult, sexually mature individual, but always undergoes further modifications, whereby it develops into either a polyp or a medusa. ”

“ Nevertheless the small group of Actinelida is very important, being probably the ancestral group from which all other Acantharia have been phylogenetically derived. These other Acantharia, with twenty regularly disposed radial spines, represent the two large groups of Acanthonida and Acanthophracta. For short and clear distinction of these two groups of Acantharia, we will call the Actinelida (with irregular number and disposition of radial spines) Adelacantha, in opposition to the Icosacantha (Acanthonida and Acanthophracta) , which all possess twenty regularly disposed radial spines. ”

“ Although apparently sedentary creatures, the Actiniæ often prove themselves to be capable of moving about at will over any portion of their subaqueous domain. Having selected a particular spot, they will ofttimes remain stationary there many consecutive months. A smooth anemone that had been domesticated for a whole year in my aquarium thought fit to change its station and adopt a roving life, but at last 'settled down,' much to my surprise, upon a large mussel suspended from the surface of the glass. ”

“ They may, on the contrary, be dropped from the parent in different stages of development, sometimes even after the tentacles have begun to form, as in Figs. 8, 9. Neither is it by means of eggs alone that these animals reproduce themselves; they may also multiply by a process of self-division. The disk of an Actinia may contract along its centre till the circular outline is changed to that of a figure 8, this constriction deepening gradually till the two halves of the 8 separate, and we have an Actinia with two mouths, each surrounded by an independent set of tentacles. ”

“ Very rarely (Acanthochiasma) each two opposite spines are united so that ten diametric bars cross in the middle of the central capsule. Whilst in the great majority of Acantharia these twenty radial spines are present, the small group Actinelida is characterised by the possession of an inconstant, often very large number, sometimes over one hundred. Among these Actinelida are probably to be found the stem-forms of the whole legion. ”

“ All Actiniæ are not attached to the soil like those described above, nor do they all terminate in a muscular foot, some being pointed or rounded at their extremity. Many are nomadic, wandering about at will during their whole lifetime, others live buried in the sand or mud, only extending their tentacles beyond the limits of the hole where they make their home ”

“ THE PARASITIC ANEMONE.
This species (Actinia parasitica of Couch) takes rank among the largest of our native Actiniæ, being only exceeded by fine specimens of A. dianthus. It frequently attains a height of four inches, and a diameter of two and a half. It is of a columnar form, nearly equal in diameter throughout, but commonly a little expanded at the base, which slightly spreads over the substances to which it adheres.
The colouring of the body, though subject to some variation, always maintains such an uniformity of style and pattern as to render it easy of identification at all times. ”