CHAPTER VII.
THE ASCIDIANS, BARNACLES, SEA-CUCUMBERS,
NAKED MOLLUSCS, SEA-WORMS, ETC.
A group of Ascidians forms a very curious object for the Aquarium, their forms being singular, and sometimes delicate as a transparent egg-shell. The group delineated in [Plate VII.] will convey some idea of the general appearance of these creatures, whose habitations might be taken for a store of fairy pitchers, placed snugly in their submarine china-closet for extra safety, and partially covered with sea-weed as a further means of concealment. There are above fifty native species, varying greatly in appearance. They may be found at the extreme verge of low water, many having the aspect of pellucid bags, formed of a substance between jelly and leather; while others present a far more robust and rugged appearance, both in form and texture. Some are very dingy in colour, but a few species—more rarely found—are very attractive, and sometimes brilliant, in their hues.
Plate X.
1. Actinia crassicornis.
2. A group of Serpula contortuplicata.
The Barnacles must not be omitted in furnishing an Aquarium, nor the fable connected with the Common Barnacle (Pentelasmis anatifera), in which it is affirmed that the Barnacle Geese were their offspring. Our old naturalist Gerard not only gives a detailed account of the transformation by which this wonder of the good old times was accomplished, but positively illustrates his description with an engraving, in which the metamorphosis is seen in progress.
The tube-like cells of the Serpulæ have some resemblance to the cells of the Common Barnacle, but that of the solitary Serpula, Serpula tubularia, is much taller, often rising a foot from the substance it adheres to. The fan-like feathers forming the feeding, and, perhaps, also the breathing apparatus, of Serpula contortuplicata, are exceedingly rich in colour, as is also the member which acts as a “cork” to the tube when the feather-like tentacles are withdrawn, and which is familiarly termed the “stopper;” for when, on alarm, the feathers are suddenly drawn in, the “stopper” immediately follows, shutting up the opening of the tube in a very perfect manner. This organ is often of a rich orange, and the feathers a brilliant scarlet, though they are sometimes pale, or nearly white, as shown in [Plate X.] These fan-like organs, termed feathers, appear to act as breathing organs, by separating the oxygen from the currents of water which pass between their fibres. The Sabella, an allied tribe, forms its tube of mud; while that of the Serpula is always of hard shell. The golden-combed worm, Amphitrite auricoma, another singular creature of this class, may be best alluded to in this place. Just below the cork-like head, when it leaves its tubular shell, are the scarlet gills, slightly resembling those of fishes, and across the head the golden comb-like appendage is expanded, from which it derives its popular name. When the animal retires within its tube, the upper part of the head has, like the Serpulæ, all the appearance of a cork or small stopper. This creature is one of the most curious of its class.
The Balani, or Acorn-shells, which are generally parasitic, fixing themselves to the shell of the Whelk or some other univalve, spread their crimson tentacles when seeking food exactly in the manner of the Serpulæ, the feathery filaments forming a kind of living casting-net, as it has been observed, in which the minute Annelid or Infusory is entangled and devoured. Two Balani are represented in [Plate VII.] on the shell of a common Whelk.