STAUROMEDUSAE UK
An online guide to the Stalked jellyfish (Stauromedusae) found
around the coastal waters of the United Kingdom and Ireland.
Includes notes on their identification, and where and how to find them.
27. Lucernaria convolvulus. {fig. 3.)
Lucernaria convolvulus. a, The natural size, side view; b, a view of the oral disk expanded, natural size; c, a few of the filaments in the stomach, magnified.
This species resembles the L. auricula, which we have figured in this Magazine, V. 44.; but besides some minute
differences in their external anatomy, which satisfactorily distinguish them, there are some discriminative peculiarities in their habits. Lucernaria auricula swims with ease, and is not greatly disinclined to the exercise; it expands the tentacula, and inflects them within the cup of its disk with a rapid contraction, and is altogether rather an active creature. It is not so with L. convolvulus, which will remain for days on one site; and when detached by force from its hold, a pellicle of skin is left on the spot, as if the connection had not been broken without injury to its structure. Its motions are all slow, and it is little susceptible of external impressions, so that it will continue expanded until one is weary of watching ; and when it wills to contract, it does so lazily, and slowly again resumes its former position. Such is the result of observations made on two individuals taken in Berwick Bay; and they correspond with those of my friend Dr. Coldstream, who had previously taken this species on the shores of Devonshire. "I find," he says, "the animal very hardy. It is constantly in a state of expansion, and does not contract except when very rudely handled. One specimen has lived with me for three weeks, although the water has not been very often changed."
Lucernaria convolvulus is about an inch in height, of a uniform liver-brown colour, smooth, adhering by a circular disk, above which there is a deep stricture; the disk even, strengthened by an internal cartilaginous lamina, which rises up the short peduncle, and forms a minute hollow firm centre. The margin of the oral expansion is somewhat thickened, and divided into eight equal arms, each furnished with a tuft of numerous short tentacula tipped with a gland, and brighter coloured than the body. The interior is hollowed like the blossom of a flower, the square extensible mouth projecting in the centre; and in the space between the arms there is a complicated structure, composed apparently of a series of foliaceous processes arranged on each side of a white line that seems to spring from the sides of the mouth. These processes, apparently branchial, are formed by the complicated foldings of a thin membrane, attached by one side in the manner of a mesentery : there are no vessels in the membrane; but some portions of it exhibit, when magnified, a kind of network of irregular cells, and the outer free edge is bounded by a thread-like line. The white central line which divides them is formed of small roundish bodies, arranged in two or three close series; and some of these ova can at times be traced along the margin of the circumference to the tentacula.* The latter are cylindrical, hollow, and terminated,
* " When I first procured it, the * two rows of spots' running from the mouth along each arm were prominent, and of a dark reddish-brown colour. Since that time they have increased in size, and have become studded with numerous white oval bodies, which I suppose to be ova. I see some of these have made their way into the web connecting the arms, but I have not observed any expelled from the body." {Dr. Coldstream.)
with a globular head, which is certainly imperforate. The stomach is a loose thin-plated extensible bag; to the inner surface of which are attached numerous filiform caeca, that, after removal from the body, retain their irritability for a long time, and writhe themselves like a knot of worms. (fig. 3. c.).
Both our specimens were found near low water-mark, adhering to the fronds of Fucus siliquosus.
I may remark that in the figure which Montagu has given of Lucernaria auricula {Lin. Trans, ix. 113. tab. 7. fig. 5. 1808.), there is no appearance of marginal tubercles between the tufts of tentacula, whence it may be inferred that it has been drawn from a specimen of the present species with only seven arms.
Ref: L. convolvulus, Johnston in Mag. Nat. Hist. Vol. viii. page 59, fig. 3. 1835.
This is the first description of Craterolophus convolvulus.
See - Species account for Craterolophus convolvulus
