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.
V. — Notes on Depastrum cyathiforme, Gosse.
By E. S. Russell.
[Plate v.]
M. Sars, in 1846, was the first to describe and figure this interesting little Lucernarian. He discovered it near Bergen and described it under the name of Lucernaria cyathiformis as follows : — " Semipollicaris, stipite disco circulari, repando sese affigente ; corpore cyatliiformij margine dilatata, repanda circulari, Integra (s. non in radios divisa) tentaculifera, tentaculis saepissime in fasciculis 8 fere continuis, ad marginem corporis dispositis ; organis generationis 8, binis approximatis " (Faun. lit. Norveg. no. 1, p. 26, tab. iii. figs. 8-13).
Shortly afterwards it was found in great abundance by Mr. David Landsborough, Jun., at Southend, Arran, and also by Dr. Landsborough at Corriegils, Arran. The specimens were identified by Mr. Joshua Alder as Lucemaria cyathiformis Sars, and he sent a drawing to Mr. George Johnston, who, on the strength of this drawing, incorporated the species in his * Hist. of Brit. Zoophytes, vol. i. p. 475 (London, 1847).
Gosse (Synopsis Brit. Actinia, 1858) then founded the genus Depastrum for specimens which he found at Weymouth, which he regarded as identical with the Lucemaria cyathi-forviis of Sars. Next year some small specimens were found by Allman (Rep. Brit. Assoc. Aberdeen, 1859) in the Orkney Isles, which seem to have been immature specimens of Depastrum cyathiforme, Gosse. It does not appear to have been recorded at any other locality until found by Beaumont at Port Erin, Isle of Man (' Fauna of Liverpool Bay' iv. : Liverpool, 1895). He mentions also a specimen from Plymouth.
In the month of July 1903 I rediscovered Depastrum on the shore at West Berman, Southend, Arran ; and in August, while at the Millport Biological Station, near the Lion Rock, Millport, and also near the old castle on the east side of Little Cumbrae. The animal seems to have a wide distribution, and I have no doubt that a careful search would reveal its presence in many localities from which it is hitherto unrecorded.
I found Depastrum in large numbers under stones at about half-tide, and also farther out. It adheres very firmly to the underside or occasionally round the edges of fairly large stones, so firmly that it has to be scraped off with a knife. It is very local in its distribution, but generally abundant where it does occur, though at one locality in Little Cumbrae I found only a few scattered individuals. It is difficult to account for its local distribution, but in my experience it is never found in muddy localities nor in spots where there is much decaying seaweed. It occurs well up the beach, and appears to be quite a hardy form. In Arran my largest specimens were got near low-water mark, but at Cumbrae large specimens occurred more plentifully halfway up the beach. In its natural conditions it is almost always pendent, being incapable of supporting itself with stalk extended and erect, on the upperside of a stone. When watched carefully in confinement it is seen to turn the widely expanded bell-like umbrella in different directions, as if searching for food. It appears to be quite incapable of re-fixing itself after having been dislodged from its resting-place.
The stalk is very contractile, as is also the rim of the umbrella. Four muscles, which extend up the taenioles (PI. v., tm.), are the agents for contracting the stalk, while the margin is contracted by a circular muscle (cm.) which passes round outside the insertion of the tentacles, and in contracting pulls the margin well over the tentacles, leaving only a hole in the centre, through which the tips of some of the tentacles appear. I may here remark that it is only in partly contracted individuals that several rows of tentacles are seen ; in fully expanded adult individuals there do not appear to be more than two rows. Haeckel, in his diagnosis of this species (' System der Medusen '), describes it as having the tentacles in several rows. Furthermore, none of my specimens reach the dimensions noted by Haeckel (8-10 mm. for length of stalk, length of umbrella, and breadth of umbrella), the largest I have seen having a stalk only 7 mm. long, while the usual size of good-sized specimens is 4 mm. for length of stalk, 6 mm. for height of bell, and 5-6 mm. for breadth of same. These specimens seemed mature, having well-developed gonads.
There appear to be two forms of the species among my specimens — one as figured, the other with a much sharper distinction between stalk and umbrella, and with the breadth of the umbrella as great as, or even greater than, the height of the umbrella. This latter seems to be the typical form, for Haeckel describes the umbrella as being almost as high as broad. The measurements of a medium-sized individual of this latter form are: — Length of stalk 3 mm.; height of umbrella 4 mm ; breadth of umbrella 4.8 mm. The smallest specimen I possess measures respectively 1 mm., 1.1 mm., and 1.4 mm.
The sexes are distinct, but, so far as I can make out, indistinguishable in external appearance. The gonads are typically in four double rows, but I have a specimen with only three gonads and three lobes to the manubrium. Indeed, the animal is very variable, especially as regards the number of fascicles of secondary tentacles. The ova and spermatozoa are very minute and very numerous. I attempted five times in August to fertilize artificially, but failed each time, chiefly, I believe, on account of the immaturity of the spermatozoa.
In the stomach of Depastrum I have noted the remains of a small crustacean (probably a Copepod). When kept in confinement unattached to a stone they sometimes void a floccular mass, along with one or two phacellae, which looks like a portion of the stomach epithelium. The tentacles also are apt to slough off. It is very difficult to kill them well expanded, but I have obtained good results by carefully narcotizing with 30% alcohol.
