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1843. Paludicella articulata. Thompson, Rep. Brit. Assoc., p. 285.
Iconography.—The original figures are those of Van Beneden (Bul. Ac. Brux.), Van Beneden (Mém. de l'Ac. Brux.), Gervais, Allman, Johnston, Hancock, and Leidy.
HABITAT.-On submerged stones in still and slowly running water. Eminently lightshunning.
LoCALITIES.—British : Regent Canal, London; Chelmer Canal, Essex; Grand Canal, Dublin; Union Canal, Edinburgh. G. J. A.—Lough Erne, Ireland. Mr. Wm. Thompson.— Bromley Lough, Northumberland. Mr. Hancock. Foreign : Lake of Lucerne, Lake of Zurich, Lago di Como, and Lago di Lugano. G. J. A. —Near Paris. Gervais-Belgium. Dumortier and Van Beneden.—Prussia. Ehrenberg.— Near West Point, in the United States; abundant. Prof. Bailey. The specific name articulata, originally applied to this species by Ehrenberg, was sufficiently significant, so long as the animal was described as a species of Alcyonella; it is now, however, quite inapplicable, for it possesses no specific meaning whatever, being expressive of one of the most striking characters on which the senus formed for it has been founded. I, therefore, entirely agree with M. Van Beneden, in admitting the necessity of changing the original specific name, and willingly adopt that of Ehrenbergi, proposed for it by the learned Belgian naturalist in honour of its discoverer. P. Ehrenbergi is very widely distributed, and we can scarcely account for its having so long escaped notice, except by supposing that its resemblance to some of the confervoid algae caused it to be overlooked. The coenoecium is partly free, partly adherent. The adherent portion extends over the under surface of stones as a branched confervoid growth, the branches being given off either opposite to one another in pairs, or else singly, the development of the opposite branches being in the latter case suppressed. Besides the portion which thus continues closely adherent to the supporting surface, numerous branches remain quite free, growing in luxurious specimens frequently to the length of two inches, and being themselves ramified in a manner quite similar to what occurs in the adherent portion. The structure of both adherent and free portion is similar, every branch consisting of a series of symmetrical clavate cells, each of which is attached by its narrow extremity to the wide extremity of the cell below it, from which its cavity is separated by a perfectly formed septum, visible through the transparent walls of the cell; the entire coenoecium thus presents a very striking and elegant concatenated appearance. The orifices are unilateral, and are placed at the extremity of little tubes, which project obliquely forward from the side of the cell near its wide end. The branches are given off at nearly right angles from the wide part of the cell, one at each side of the tubular orifice, and are thus (unless when the suppression of one of them takes place) situated in pairs one opposite to the other, with the tubular orifice between them. The ectocyst is a pellucid membrano-corneous tunic, nearly colourless in young specimens, but acquiring a dark brown colour by age. The polypide has but sixteen tentacula, springing from the margin of the orbicular lophophore, in a perfectly infundibulate crown. Van Beneden” describes the occurrence of what he terms “hybernacula,” in Paludicella Ehrenbergi. These hybernacula are gemmae, which, under the influence of a favorable temperature, would have grown into the ordinary lateral branches of the Polyzoon, but which towards the commencement of winter acquire a conical form, and then become for a while arrested in their development. In this state, surrounded by a firm membrane of a blackishgray colour, they continue until the following spring, when the investing membrane splits to allow of the elongation of the branch. In no instance have I witnessed the hybernacula in the specimens of Paludicella collected in Britain. P. Ehrenbergi is an exceedingly timid little animal, and a specimen may be for hours under observation before the polypides will venture to issue from their cells, and then it is often for only a few seconds at a time, that they will continue visible. It is eminently a lover of obscurity, being only found in such situations as are not exposed to the direct influence of daylight; the most luxuriant specimens I have met occurred under the arches of viaducts on the Grand Canal, near Dublin; and in similar situations elsewhere, where the constant obscurity in which they live is never interrupted by a single ray of direct daylight. The species occur all through the year in still and slowly running water, but is most abundant during the summer and autumn.
After a careful consideration of the animal described by Mr. Hancockf under the name of P. procumbens, I have been unable to agree with this naturalist in considering it a distinct species. The main character on which Mr. Hancock relies, is the supposed smaller number of tentacula in his species, a belief to which he was naturally lead in consequence of the figure of P. Ehrenbergi given by me in the ‘Proceedings of the Royal Irish Academy, 1843,” having been erroneously engraved with twenty-six tentacula. Mr. Hancock also relies on the less densely and luxuriantly branched condition of his specimens, and on a smaller size and difference of colour in the cells, as grounds for distinction, but I believe these to be characters
* Dumortier and Van Beneden, ‘Hist. Nat. des Pol. Com. d'eau douce, Mém. servant de Complément au tome xvi des Mém. de l'Acad. Roy. Bruxelles.” t Hancock, in ‘Ann. Nat. Hist, 2d series, vol. v., p. 201.
depending solely on age and accidental circumstances of growth. I cannot think, therefore, that there are sufficient reasons for considering the P. procumbens of Hancock as distinct from P. Ehrenbergi.
I have also been unable to find, in the characters assigned by Dr. Leidy” to the species occurring in the neighbourhood of Philadelphia, and named by him Paludicella elongata, sufficient grounds for the separation of the American form as a distinct species from the European one. A slight difference in the length of the cells cannot afford a valid specific difference, and this view is fully borne out by the figure which accompanies Dr. Leidy's paper.
* Leidy, in ‘Proc. Acad. Nat. Sci. of Philadelphia, vol. v., p. 321.
Name.—A diminutive noun, formed from urna, an urn, in allusion to the urn-shaped figure of the articulations.
We find, in the fifth volume of the ‘ Proceedings of the Academy of Natural Sciences of Philadelphia, a new Polyzoon described by Dr. Leidy under the name of Urnatella gracilis. It resembles, as Dr. Leidy informs us, a miniature Isis hippuris, and was discovered growing upon the under side of stones, in the River Schuylkill, near Philadelphia. Dr. Leidy accompanies his communication with a figure of the coenoecium; and though he had not succeeded in detecting the polypides, he felt himself justified in viewing the production in question as a true Polyzoon.
At a subsequent meeting of the Academy (‘ Proc. Acad. Nat. Sc. of Philadelphia,” vol. vii. p. 191), Dr. Leidy again offers some remarks on Urnatella gracilis. Since his previous communication, he had detected the polypides, and had also in other respects succeeded in making a more satisfactory examination of the new Polyzoon, so that he now finds it necessary to alter in some points his previous description.
His account is confined to a generic and specific diagnosis, from which it appears that Urnatella gracilis is a most remarkable animal, and one of the most beautiful of the freshwater Polyzoa. The following are the characters given by Leidy in his amended diagnosis :
Generic character.—“Coenoecium consisting of a series of segments up to eighteen in number, and forming free semi-erect curved stems, attached only by the base of the lowest segment. Segments, excepting the three last ones, simple, urniform; the antepenultimate and the penultimate oblong, with simple or compound branches of the same form ; the last segment or active polyp is campanulate, and is supplied with cylindrical ciliated arms, arranged in a circle round the mouth.” Leidy.
Species unica. Urnatella gracilis, Leidy.
Specific character—“Stems single or in groups up to six in number, attached at the lower extremity by means of a sienna-coloured granular substance. Urniform segments 225 mm. long by 18 mm. broad, becoming smaller towards the free end of the stems; body portion of each urniform segment translucent, whitish, with sienna-coloured transverse striae and punctae, and having on each side near the bottom a roundish process, the remains of former branches; the narrow top and bottom portion of the segments brown in colour and annulated. The antepenultimate and penultimate segments and their branches oblong, translucent. Polyp. 225 to 45 mm. long, campanulate ; expanded, mouth circular, the diameter equal to the length of the body, surrounded by fourteen cylindrical, ciliated, retractile arms. Stems up to 4 mm. in length.” Leidy.
SYNoNYMs.—1854. Urnatella gracilis. Leidy, Proceedings Acad. Nat. Sci. of Philadelphia, vol. v., p. 321. (Original figure of the coenoecium.) 1854. Urnatella gracilis. Leidy, Proceedings Acad. Nat. Sci. of Philadelphia, vol. vii, p. 191.
Iconography.—Original figures of the coenoecium by Leidy.
Besides the two short notices contained in the references given above, there is no other
published account of this remarkable genus, and zoologists cannot but look forward with impatience to the fuller description promised by its discoverer.
While the present sheets were passing through the press, I received a note from Pro
fessor Leidy, along with a pencil sketch of the expanded polypide, from which I have given the accompanying woodcut. “The anatomy of the animal,” writes Dr. Leidy, “is easily ex
* From a pencil sketch furnished by Dr. Leidy.