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Genus IV. AlcyONELLA, Lamarck, 1816.
Name.-A diminutive noun, formed from Alcyonium, a genus of marine Actninozoal Radiata.
The animal originally described by Pallas, under the name of Tubularia fungosa, and by Bruguière under that of Alcyonium fluviatile, was assumed by Lamarck as the type of a new genus which he named Alcyonella ; but, deriving its characters from the very incorrect description and figures of Bruguière, Lamarck's definition of the genus is necessarily erroneous,
Some naturalists insist on the identity of the genera Alcyonella and Plumatella, and go so far as to maintain that the animal described under different names, by Pallas, Bruguière, and Lamarck, possesses no essential character to distinguish it even specifically from P. repens or P. campanulata, the difference being solely the result of accidental causes-especially the form and size of the object to which it is attached-operating on it during its growth, and thus influencing its development. The author who has most elaborately defended this view is M. Raspail, and a similar opinion has been advocated by Ehrenberg and Siebold. After, however, much attention to the subject, I have satisfied myself that there are sufficient grounds for keeping the two groups generically distinct. It is quite true that, in its young state, Alcyonella has its tubes distinct, creeping along the surface of the supporting body, and in this condition, I admit that it cannot be distinguished from a Plumatella, but it is only in its early youth that it presents this form. Plumatella, on the other hand, preserves a distinctness of its tubes throughout its whole existence. I have found very large specimens of Plumatella under precisely the same circumstances as those in which we meet Alcyonella, and yet without the slightest tendency to assume the form of the latter
argument, which strongly supports the view here taken, is derived from the fact that Alcyonella has not yet been detected in Ireland, * though Plumatella repens is exceedingly abundant throughout the island, frequently presenting the utmost luxuriance, and yet invariably preserving a total distinctness of its tubes, no matter what the form or size of the object on which it grows.
In distinguishing the species of Alcyonella, I have employed characters drawn chiefly from the general habit of the animal, the structure of the cænæcium, and the shape of the statoblasts. We have seen, in the anatomical section of this monograph,† that the ectocyst in the genera Alcyonella and Plumatella sometimes presents upon its surface the appearance of a transparent longitudinal furrow running along the length of each tube, commencing in the vicinity of the orifice as a triangular notch-like space, and passing into a prominent keel as
* In my Synopsis, published in the 'Annals of Natural History,' 1841, I recorded Alcyonella stagnorum as a native of Ireland. The animal, however, there alluded to under this name is really the Polype à Panache ; and I was led into this error from adopting at that time the opinion of Raspail, Johnston, and other naturalists, that Trembley's animal was identical with the A. stagnorum of Lamarck.
+ Vide supra, p. 13.
it recedes from this point. The presence of the longitudinal furrow constitutes an important specific character, and its value is enhanced by its being of easy application; it occurs in two out of the three species of Alcyonella. Another very valuable character is obtained from the shape of the statoblasts.
The ordinary or free statoblasts, both in Alcyonella and Plumatella, present two different shapes; in some species they are broadly elliptical, the diameters of the ellipse being to one another pretty nearly in the ratio of 2 : 3; in others again they are narrow, the diameters being nearly as 1:2. The terms broad and elongated therefore, as applied to the ova in the following diagnosis, are to be understood as expressing this difference of shape.
Generic character.-Cænæcium composed of membrano-corneous branched tubes, which adhere to one another by their sides ; orifices terminal. Statoblasts elliptical, with an annulus but without marginal spines.
Number of known species three.
1. Alcyonella fungosa, Pallas. Pl. III.
Specific character.—Cænæcium fungoid, formed of numerous branched vertical tubes destitute of a furrow. Statoblasts broad.
SYNONYMS.—1768. Tubularia fungosa. Pallas, Descript. Tub. Fung. Nov. Comment. Acad. Sci.
Imp. Petropol. tom. xii, p. 565, tab. 14. (Original figures.) 1782. Spongia lacustris. Schmiedel, Icones Plantarum et Anal. Partium. 1786. Leucophra heteroclita. Müller, Animal. Infusor. p. 158, tab. 22, fig. 27-31.
(Locomotive embryo, original figures.) 1789. Alcyonium fluviatile. Bruguière, Encyc. Méth. 1789, p. 24 , pl. 472, fig. 3.
(Original figure, bad.) 1802. Alcyonium fluviatile. Bosc. Vers. vol. iii, p. 132. 1816. Alcyonium fluviatile. Lamouroux, Pol. flex. p. 354. 1816. Alcyonella stagnorum. Lamarck, An. sans Vert. 1st edit. vol. ii, p. 102. 1820. Alcyonella stagnorum. Schweigger, Handbuch der Naturg. p. 423. 1821. Alcyonella stagnorum. Lamouroux, Exposit. Méth. p. 71, tab. 76, fig. 5-8.
(Figures copied from Bruguière.) 1824. Alcyonella stagnorum. Lamouroux, Enc. Méth. 1824, Zooph. p. 38. 1828. Alcyonella fluviatilis vel A. ultimus evolutionis gradus. Raspail, Hist. Nat.
de l’Alcyonelle fluv., Mém. de la Soc. d'Hist. Nat. de Paris, tom. iv,
p. 130, pl. 12-16. (Original figures.) 1828. Alcyonella stagnorum. Meyen, Isis, tom. xxi, p. 1225, pl. 14. (Original
figures.) 1831. Alcyonella stagnorum. Ehrenberg, Symbolæ Physicæ Evert. Dec. 1, Pol.
1834. Alcyonella stagnorum. Blainville, Man. d’Actin. p. 491, pl. 85, fig. 8.
(Figure copied from Raspail.)
1835. Alcyonella stagnorum. Carus, Tabulæ Illustrantes, pars 3, tom. 1. (Figure
locomotive embryo, copied from Meyen.) 1836. Alcyonella stagnorum. Dumortier, Mém. sur les Pol. comp. d'eau douce, p. 24. 1836. Alcyonella stagnorum. Lamarck, An. sans Vert., 2d edit., vol. ii., p. 116. 1837. Alcyonella stagnorum. Teale, Trans. Phil. and Liter. Soc. of Leeds, vol. i,
part 1, p. 116, pl. 12. (Original figure.) 1837. Plumatella campanulata, var. B. dumetosa. Gervais, Ann. Sc. Nat., 1837, p. 78. 1838. Alcyonella stagnorum. Johnston, Hist. Brit. Zooph., 1st edit., p. 311, pl. 45.
(Figures partly original, and partly copied from Raspail.) 1839. Alcyonella fluviatilis. Gervais, Ann. Franc. et Etrang. d’Act., tom. iii, p. 135. 1839. Alcyonella. Van Beneden. Bull. de l'Acad. de Brux., tom. vi, part 2, p. 276,
figs. 3, 3'. (Original figures.) 1840. Alcyonella fluviatilis. Gervais, Dict. Sci. Nat. Suppl. art. Alcyonelle.
(Original figures.) 1847. Alcyonella stagnorum. Johnston, Brit. Zooph. 2d edit. p. 391, pl. 74.
(Figures partly original, partly copied from Raspail.) 1848. Alcyonella stagnorum. Siebold, Lehrbuch der Vergleich. Anat., § 38. note 1;
§ 40, note 2 ; 43, note 4. 1848. Alcyonella fungosa. Van Beneden, Recherch, sur les Bryoz. fluv. de Belg.,
p. 18, Mém. de l'Acad. Roy. de Belg., 1848. 1848. Alcyonella fungosa. Dumortier et Van Beneden, Hist. Nat. des Pol. comp.
d'eau douce, Mém. servant de complément au tom. xvi des Mém. de l'Acad.
Roy. des Sci. de Brux. (Original figures.) 1849. Alcyonella anceps. Dalyell, Rare and Remark. Anim. of Scotland, vol. ii.
Iconography.—The original figures are those of Pallas, Müller (embryo), Bruguière, Schmiedel, Raspail, Meyen, Teale, Johnston, Van Beneden (Bull. de l'Acad. de Brux., 1839), Van Beneden (Mém. de l'Acad. de Brux., 1848), Dumortier and Van Beneden (Hist. Nat. des Pol. Comp.), Dalyell.
HABITAT.-Stagnant and slowly running waters, canals, &c., attaching itself to stones, floating timber, and submerged branches of trees; loving obscure places.
LOCALITIES.—British: Regent's Canal, London, attached to the sides of the docks, abundant; Chelmar Canal, Essex, abundant. G. J. A.-London and East India Docks, on the Thames, attached to floating timber, abundant. Mr. Busk, Mr. Quekett, Mr. Bowerbank, and G. J. A.-In brackish water, near Ipswich. Mr. Wigham.-- Near Leeds. Mr. Mathewman.—Berwickshire. Sir J. Graham Dalyell.—It is, probably, generally distributed through England. No Irish locality.
Foreign.-France. Bruguière, Raspail, Gervais.-Belgium. Van Beneden (Bull. de l'Acad. de Brux.) Dumortier and Van Beneden (Hist. Nat. des Pol. comp.)—Germany, Meyen.-Russia. Pallas.
Alcyonella fungosa presents itself in the form of brown fungoid masses of size and shape, attached to the surface of different fixed objects, as stones, pieces of wood, fresh-water shells, &c. The masses frequently acquire a considerable size, weighing upwards of a pound. They are often irregularly lobed, and when they grow upon the surface of a cylindrical body, as a twig on the stem of some aquatic plant, usually surround it so as to assume a somewhat spindle-shaped figure, gradually diminishing in thickness from the centre towards the extremities. They are fond of attaching themselves to the branches of trees which dip into the water, and then constantly exhibit lobed, pear-shaped masses pendant from the extremities of the
sprays. When a living specimen is examined in the water, its whole surface seems covered with a whitish down, which a slight examination shows to be occasioned by the protrusion of innumerable polypides. When removed from the water, the polypides shrink back into their cells, and the surface then seems covered with a gelatinous investment, caused by the soft, papilla-like, extremities of the tubes. These extremities contract no adhesion to one another, like the rest of the tubes, and the ectocyst, as it passes over them, becomes very delicate and transparent; in dead specimens they shrivel up and disappear, and then the surface of the mass presents a multitude of closely applied hexagonal or pentagonal orifices. The whole production now assumes the appearance of a spongy, honeycomb-like mass, and this has not unfrequently been mistaken for a fresh-water sponge. A vertical section shows it to be composed of a vast number of tough, membrano-corneous-branched tubes, closely adherent to one another, and each opening on the surface by one of the angular orifices, just mentioned. Imperfect transverse septa may be seen at the origin of many of the branches. The tubes, towards the end of summer, are loaded with mature statoblasts, which, on the rupture of the cænæcium, escape in great numbers into the surrounding water.
The colour of the living mass varies somewhat with the nature of the food and the state of depletion at the time, the contents of the stomach being visible through the transparent portion of the tubes. When the stomach is not filled with food, so as to impart an adventitious colour to the mass, the latter is generally of a light-brown, or gray, upon the surface, and of a darker brown in section. It is in perfection during the summer and autumn; in winter, nothing is to be found of it but the empty and decaying cænæcium.
A. fungosa is a widely distributed Polyzoon, having been found in Russia, France, Prussia, Belgium, and the British Isles. It is curious enough that, though it is common in England and Scotland, it has never yet been found in Ireland, where all the other British genera are abundant. It prefers stagnant and slowly running waters. Some of the largest specimens I have seen were in the Chelmar, a sluggish river in the county of Essex, which has been widened and deepened into a canal, for the purposes of inland navigation.
2. Alcyonella Benedeni, Allman. Pl. IV, figs. 5–11.
Specific character.—Cænæcium fungoid; formed of numerous branched vertical tubes, which are emarginate at the orifice, and furnished with a furrow. (Free) Statoblasts elongated.
SYNONYM.–1850. Alcyonella Benedeni. Allman, British Association Report.
The present well-marked species I have great pleasure in dedicating to M. Van Beneden, a naturalist who has not only done more than any one else in the particular department to which this monograph is devoted, but who has enriched our knowledge of the lower animals generally, by contributions numerous and valuable.
A. Benedeni occurs in spongy masses attached to twigs, and other fixed bodies, and resembling A. fungosa in their general appearance. They would seem, however, never to attain to so large a size as the latter, the largest specimens I have seen, measuring about three inches in length, and an inch in thickness at the thickest part. The tubes are closely adherent to one another until within a short distance of their terminations, when they become free. The ectocyst is dark brown, becoming rather abruptly lighter in the vicinity of the orifices, where the peculiar characteristic furrow commences by a triangular notch-like space, and then passing down as a narrow slit-like line, is finally lost where the adhesion of the tubes begins. When withdrawn from the water, the tubes seem terminated by a little papilliform body, formed by the endocyst, over which the ectocyst is continued as a very delicate, transparent, and colourless membrane. In extreme retraction, the papilliform terminations are entirely withdrawn into the remainder of the tube.
The statoblasts are of two kinds—free, and adherent. The free statoblasts are narrowly elliptical, approaching to bean-shaped; the disc is brown, minutely mainillated; the annulus is dull yellow, widely overlapping the disc, especially on the more convex side. These statoblasts are found in immense numbers towards the end of summer, lying quite free in the interior of the tubes, and, on the rupture of the latter, escape, and instantly rise to the surface of the water. Besides these bodies, others much less numerous are also found in the present species, but are always attached to the inner walls of the tubes. They are broadly elliptical, enclosed in a pergamentaceous shell, like the free statoblasts, but with a very narrow margin. Of their real import we are ignorant.
I have met with A. Benedeni only in one locality, namely, the River Chelmar, in Essex, where it existed in abundance, along with A. fungosa and the following species:
Specific character.—Cænæcium flabelliform, composed of branched prostrate tubes, furnished with a furrow. Statoblasts broad.
SYNONYMS.—1848. Alcyonella flabellum. Van Beneden, Recherches sur les Bryozoaires fluv. de
Belg., p. 19; Mém. de l'Acad. Roy. de Belg., 1848. (Original figures.) 1850. Alcyonella flabellum. Allman, Proc. Roy. Irish Acad., vol. iv, p. 470.
* Vide supra, p. 40.