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5.

Diagnosis, Synonymy, And Natural History Of The Genera And Species.

Cristatellidje. Genus I. Cristatella, Cuvier, 1798. Name.—A diminutive noun formed from crista, a crest, in allusion to its tentacular plume.

The genus Cristatella was established by Cuvier, for the little animal originally described by Rosel under the title of "Der Kleinere Federbusch Polyp mit dem ballenformigen Kbrper." Its characters were given in the 'Tableau Elementaire des Animaux,' published in 1798, and it is the first generic group constituted for any of the fresh-water Polyzoa, hitherto all confounded together in discordant and unzoological associations. Rosel's animal, however, was unknown to Cuvier, except from the figures and descriptions left us by its discoverer; and it was not until Turpin and Gervais many years afterwards rediscovered it, having hatched it from statoblasts found in the Canal d'Ourcq, in the city of Paris, that any additions were made to the original account left us by Rbsel. Still, however, nothing was known of the animal but in its young and partially developed state, and it was only afterwards, when adult and fully formed specimens were met with, that the real nature of this beautiful Polyzoon was properly understood.

The genus, which includes as yet but a single species, may be thus characterised:

Generic character.Coenoecium sacciform, hyaline, with a common flattened discadapted for locomotion; orifices placed on the surface opposite to the disc, and arranged in several concentric marginal series. Statoblasts orbicular, with an annulus and marginal spines.

Species unica. Cristatella mucedo, Cuvier. PI. I.

Specific character.—Same as that of the genus.

Synonyms.—1755. Der Kleinere Federbusch-Polyp. Rosel, Insect. Belustig. Supp., p. 559,

tab. 91. (Original figure.) 1766. La seconde sorte de Polypes a Bouquets. Ledermuller, Amusm. Mic. 2decinq.,

p. 94, pi. 87. (The figures are imperfect copies from Rosel.) 1798. Cristatella mucedo. Cuvier, Tab. Elem., p. 656.

1816. Cristatella vagans. Lamk., An. sans Vert., 1st edit., vol. ii, p. 97.

1817. Cristatella mucedo. Cuv., Regne A., 1st edit., vol. iv, p. 68.
1820. Cristatella vagans. Schweigger, Handbuch der Naturg. p. 423.

1824. Cristatella vagans. Lamouroux, Enc. Meth. Zooph., p. 226, pi. 472.
(Figures copied from Rosel.)

1824. Cristatella vagans. Goldfuss, Naturhistorisch Atlas. (Figures copied from

Rosel.) 18.28. Alcyonella, secundus evolutionis gracilis. Raspail, Hist. Nat. de l'Alcyon. fluv.,

Me-m. de la Soc. d'Hist. Nat. de Paris, vol. iv, p. 129. 1830. Cristatella mucedo. Cuvier, Reg. An., 2d edit., vol. iii, p. 296. 1834. Cristatella mirabilis. Dalyell, Rep. Brit. Assoc., p. 604; and Edinb. New

Phil. Journ., vol. xviii, p. 414. 1834. Cristatella vagam. De Blainville, Man. d'Act., p. 489, pi. 85, fig. 7. (Figure

copied from Rosel.) 1834. Cristatella vagans. De Blaiuville, Diet. Sc. Nat., art. Cristatelle, fig. 7.

(Figure copied from Rosel.)

1836. Cristatella vagans. Lamarck, An. sans Vert., 2d edit., vol. ii, p. 110.

1837. Cristatella mucedo. Turpin, Ann. Sc. Nat., 2d series, tom, vii, p. 65, pi. 2, 3.

(Original figures.)

1837. Cristatella mucedo. Gervais, Ann. Sc. Nat., 2d series, tom, vii, p. 77, pi. 4.

(Original figures.)

1838. Cristatella mucedo. Johnston, Brit. Zooph., 1st edit., p. 308, pi. 43. (Figures

copied from Turpin.)

1839. Cristatella mucedo. Gervais, Ann. Franc, et Etrang. d'Anat., tom, iii, p. 133.

1840. Cristatella moisissure. Gervais, Diet. Sc. Nat. Suppl., art. Alcyonelle, Planches

Supplementaires, Pol. fluviatiles. (Original figures.)

1843. Cristatella mucedo. Thompson, Rep. Brit. Assoc., p. 285.

1844. Cristatella mucedo. Allmau, Ann. of Nat. Hist., vol. xiii, p. 330.

1846. Cristatella mucedo. Allman, Rep. Brit. Assoc., Trans, of Sect., p. 88.

1847. Cristatella mucedo. Johnston, Brit. Zooph., 2d edit., p. 387, pi. 73. (Figures

copied from Turpin.)

1848. Cristatella mucedo. Van Beneden, Bryoz. Fluv. de Belg., p. 16; Mem. de

l'Acad. Roy. de Belgique. 1848. Cristatella mirabilis. Dalyell, Rare and Remarkable Animals of Scotland, vol. ii. (Original figures.)

Iconography.—The original figures are those of Rosel, Turpin, Gervais in ' Ann. Sc. Nat.,' Gervais in 'Diet. Sc. Nat.' Suppl., and Dalyell.

Habitat.—In clear lakes and ponds, where it creeps slowly over the upper side of submerged stones and the stems of aquatic plants, delighting in sunlight.

Localities.British: A millpond near Little Baddow, Essex; Union Canal, Edinburgh; a beautiful little subalpine lake near Glandore, County Cork; Lakes of Killarney, Grand Canal, Dublin; a lake near Armagh, and several other Irish localities. G. J. A.— Duddingston Loch, near Edinburgh; Coldingham Loch, Berwick; a garden pond at Binns House, Linlithgowshire. Sir J. G. Dalyell.

Foreign: Lake of Lucerne; "Grand Etang," Fontainbleau. G. J. A.—Near Paris. Gervais and Turpin.—Belgium. Van Beneden.—Germany. Rosel.

The first perfectly developed specimen of Cristatella mucedo was described in 1834, by Sir John Graham Dalyell, who discovered it near Edinburgh, and perceiving it to be so very different from previous descriptions and figures, looked upon it as a new species, and named it C. mirabilis.* Adult specimens have since been found by M. Gervais, and I have met with them in abundance in Ireland, and in other parts of the British Isles.

A more interesting and beautiful animal than a fully developed specimen of Cristatella tnucedo can scarcely be imagined. The entire colony is of an oval shape, convex above and flat below, where it attaches itself to neighbouring objects. Upon the convex surface are arranged the orifices through which the polypides emerge, they are placed near the margin, and run round the entire coenoecium in three regular concentric series, which alternate with one another, and leave an oval space in the centre where no orifices exist.

In the middle of the flattened under surface is an oval disc, resembling the foot of a gasteropodous mollusc; on this disc, which is contractile, and admits of frequent change of shape, the colony adheres to neighbouring objects, or creeps about on the submerged leaves and stems of aquatic plants. From the edges of the disc a flat space extends outwards, passing beyond the external series of orifices in the form of a projecting margin, whose interior is occupied by a series of tubular cells or chambers, visible through the translucent skin, and extending in a radiating direction from the disc outwards, but possessing no external opening.

The tentacula are about eighty in number, being more numerous than in any other known Polyzoon, except, perhaps, Pectinatella, Leidy. The coenoecium is of a dull yellow, or sienna colour. The polypide is nearly of the same colour, with the exception of the intestine, which, in well-fed, healthy specimens, is light bluish-green.

The largest specimens measure about two inches in length and a quarter of an inch in breadth, and, with the polypides extended, are, at the first glance, not unlike certain hairy caterpillars, or, as M. Gervais has aptly enough suggested, the silk fabric known by the name of Chenille. Such large specimens are very sluggish, and change their place with reluctance, at least when kept in confinement; but specimens of about half an inch in length creep about on the sides of the jar in which they are preserved at the rate of several inches in the day; they generally prefer keeping near the surface of the water, and seem to be much under the influence of light; indeed, while the greater number of the fresh-water Polyzoa lurk on the under surface of stones and in dark recesses, Cristatella loves to expose itself to the full light and warmth of the sun. It differs, moreover, from all the Polyzoa with whose habits I am acquainted, in the constant pleasure it takes in maintaining its polypides in the exserted state; these, indeed, must be very roughly handled to cause them to withdraw into their cells; and the annoyance is no sooner removed than they again emerge. This exquisite little Polyzoon seems, in fact, capable of existing only under the full influence of light, and in the midst of the innumerable vortices excited in the surrounding water by the vibratile cilia of its tentacles.

The statoblasts are very characteristic. They are about fa of an inch in diameter, exclusive of the marginal spines, and, with the exception of the statoblasts of Pectinatella, which they closely resemble, are larger than those of any other fresh-water Polyzoon. They are also, with the same exception, the only ones having an orbicular shape. One face is a little more convex than the other. The annulus is wide, very distinctly cellular, and of a light yellow colour. The disc is deep reddish-brown, and elegantly mamillated. The spines

* 'Report of Meeting of British Association, held at Edinburgh, 1831.'

spring from both faces of the disc, just within the annulus, and thence radiate outwards, extending for some distance beyond the margin. The spines springing from the more convex face are somewhat longer and more numerous than the others, and alternate with them. All the spines are terminated by two, three, or four curved hooks resembling grappling-irons. Towards the end of summer, the statoblasts occur in considerable numbers in the interior of full-grown specimens, and are visible through the transparent tissues of the animal. On the death and decay of the coenoecium they are liberated, when they become attached, by means of their hooked spines, to various aquatic plants, and ultimately open for the escape of the young, by the separation of the two faces, at the commencement of the following summer. The young, on its escape from the statoblast, is at first solitary, but is rapidly multiplied by the production of gemmae.

I have never met with Cristatella later than the autumn; it seems to be strictly annual in its duration.

PLUMATELLIDJ3.

Genus II. Pectinatella, Leidy, 1851.

Name.—A diminutive noun, formed from pecten, a comb, in allusion to the form of its tentacular crown.

In the 'Proceedings of the Academy of Natural Sciences of Philadelphia' for September, 1851, a new fresh-water Polyzoon is described by Dr. Joseph Leidy, under the name of Cristatella magnified. The statoblasts of this animal resemble those of Cristatella mucedo, and it was this character which induced Leidy to refer his new Polyzoon to the genus Cristatella. It is not, however, furnished with a disc fitted for locomotion, and it has the orifices scattered irregularly over the surface, characters which bring it very near to Lophopus, but which at once exclude it from the genus to which Leidy had referred it. Of the untenableness of this association the author became almost immediately aware, and, in the next number of the ' Proceedings,' he instituted for it a new genus, with the following diagnosis:

Generic character.—" Coenoecium massive, gelatinoid, hyaline, fixed, investing bodies; orifices arranged in irregular lobate areolae upon the free surface. Lophophore crescentic. Ova (statoblasts) lenticular, with an annulus and marginal spines." Leidy.

Species unica. Pectinatella magnifica, Leidy.

Specific character.—Same as that of the genus.

Synonyms.—1851. Cristatella magnifica. Leidy, Proc. Acad. Nat. Sci. of Philadelphia, Sept., 1851. 1851. Pectinatella magnifica. Leidy, Proc. Acad. Nat. Sci. of Philadelphia, Nov., 1851.

Iconography.—No published figure.

Habitat.—" Ditches and sluggish streams; found only in shady situations; always incrusting dead branches of trees." Leidy.

Localities.—" About Philadelphia." Leidy.

It is greatly to be regretted that we have no published figure of this beautiful Polyzoon, which must well deserve the name by which the species is designated. Dr. Leidy gives us the following more detailed description of it:

"Polypidom massive, incrusting bodies, from a few inches to several feet in length, by a few lines to two inches in diameter; gelatinoid, consistent, hyaline, with numerous polypi upon

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