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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 magnifica. 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.—“Cænæcium massive, gelatinoid, hyaline, fixed, investing bodies; orifices arranged in irregular lobate areolæ 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.,
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:
“ Poly pidom 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
the free surface arranged in close irregular areolæ. Polypi furnished with two lobes, conjoined together in the form of U, enclosing the mouth at the base, and having, diverging from the margin, from 50 to 80 sigmoid tentacula arranged at the summit in the double outline of U, with the extremities of the arms of the latter inclining towards each other; lip elevated, with the base of the tentacular lobes and the lower-fourth of the inner margin of the tentacula in the vicinity of the mouth, lake or dark rose-red colour; æsophagus colourless; stomach longitudinally folded, yellowish-brown; rectum dilatable, hyaline, its extremity slightly projecting, but retractile; length from the bottom of the stomach to the top of the extended tentacula, 1; line; long diameter of tentacular expanse, , to } of a line; length of tentacula, i'o of an inch ; breadth, tooo of an inch.
“Ovum (statoblast) lenticular, brown, enclosed at the margin by a brownish-white annular cellular sheath, zoo of an inch deep upon one side, of an inch on the other, furnished at its outer edge with 14 to 16 appendages, zoo inch long, terminating in a double, rarely a triple, hooklet. Ovum (statoblast), with its sheath, thin, discoidal, bent, 3 inch broad, with its appendages enveloped in a hyaline, albuminoid mass; when ripe, floating.
“ The surface of the polype mass has the appearance of being covered with a dense mucor from the numerous tentacula projecting from it. Immediately beneath this, is a layer having a faint roseate hue, from the red colouring in the vicinity of the mouth of the polypi ; then succeeds a layer of a dirty-yellowish colour, arising from the stomachs of the animals; beneath which are numerous opaque, white, yellowish, and brown spots, which are ova in various stages of development; and, finally, the greater depth of the mass consists of a perfectly hyaline, consistent, gelatinoid substance.
“ The animal is not so irritable as Plumatella, but is, like it, capable of entirely retracting within its tube, in which state the stomach appears transversely wrinkled.
“ The ova, as they are detached from the mass, rise nearer to the surface of the water, and float.”
The luxuriance of growth of Pectinatella magnifica in the only locality which has as yet been recorded for it, is especially worthy of attention. It would seem, indeed, that the masses formed by it attain to a size which surpasses that of any other species. It is certainly one of the noblest of the fresh-water Polyzoa; and it is much to be hoped that its discoverer will not long delay in giving us a figure, with anatomical details, of so beautiful and interesting an animal.
Genus III. LOPHOPUS, Dumortier, 1835.
Name.—From dópos, a crest, and rojs, a foot.
In a historical point of view, Lophopus is the most interesting genus of the entire class. The “Polype à Panache,” discovered by Trembley, in 1741, was the first Polyzoon of which we have any record. It long continued to be confounded with species of Plumatella and Alcyonella, until Dumortier, rediscovering it in 1834, and perceiving its distinctness, assumed it as the type of a new genus, and described it under the name of Lophopus crystallinus. Though the characters given by Dumortier to his new genus are not entirely correct, yet with some alterations in his diagnosis, Lophopus must be preserved as a well-marked and easily characterised generic form.
Shortly after the original discovery of the “Polype à Panache,” the same animal was met with in England by Baker, who described it under the appellation of the “ Bellflower animal.” M. Van Beneden believes Baker's animal to be distinct from that of Trembley, and describes it by the name of Lophopus Bakeri; but there are certainly no grounds for this distinction. Indeed, I am convinced that the animal called L. Bakeri by Van Beneden, and which has been so beautifully figured by this naturalist, is entirely identical with L. crystallinus; I must therefore still consider the genus as consisting of but a single species, the original “* Polype à Panache' of Trembley.
Generic character.—Cænæcium sacciform, hyaline, with a disc which serves for attachment but not for locomotion ; ectocyst gelatinoid; orifices scattered. Statoblasts elliptical, with an annulus, but without marginal spines.
Species unica. Lophopus crystallinus, Pallas.
, Pl. II.
Specific character. -Same as that of the genus.
SYNONYMS.—1744. Polype à Panache. Trembley, Mém. sur les Pol. d'eau douce, p. 210,
tab. 10, figs. 8, 9. (Original figures.) 1746. Polype à Panache. Beck, Acta Suecica, p. 198, tab. 6, figs. 3, 4. (Figures
copied from Trembley.) 1753. Bell-flower Animal. Baker, Employment for the Microscope, p. 306, pl. 12,
figs. 15-22. (Original figures.) 1766. Tubularia crystallina. Pallas, Elenchus Zooph., p. 88. 1767. Tubularia campanulata. Linnæus, Syst. Nat., edit. xii. 1789. Tubularia reptans. Linn., Syst. Nat. cura Gmelin, p. 3835. 1789. Campanulated Tubularia. Shaw, Nat. Miscel., tab. 354. (Original figure.) 1806. Tubularia campanulata. Turton, Linn., Syst. Nat., vol. iv, p. 668. 1816. Plumatella cristata. Lamarck, Hist. des An. sans Vert., 1st edit., vol. ii,
1820. Plumatella cristata. Schweigger, Handbuch der Naturg., p. 424.
copied from Trembley.)
de la Soc. d'Hist. Nat. de Paris, vol. iv, p. 129. 1834, Plumatella cristata. Blainville, Man, d’Actin., p. 490. 1835. Lophopus crystallinus. Dumortier, Bull. de l'Acad. de Brux., 1835, p. 424,
pl. 5, 6. (Original figures.) 1836. Plumatella cristata. Lamarck, An. sans Vert., 2d edit., vol. ii, p. 122. 1837. Plumatella campanulata. Gervais, Ann. Sc. Nat., 2d ser., tom. vii, p. 78. 1838. Alcyonella stagnorum. Johnston, Brit. Zooph., 1st edit., p. 311, fig. 48, p. 314.
(Figure copied from Trembley.) 1839. Plumatella crystallina. Gervais, Ann. Franç. et Etrang. d'Anat., tom. iii,
1844. Alcyonella stagnorum. Allman, Ann. Nat. Hist., vol. xii, p. 330.
p. 395. (Figure copied from Trembley.)
Mém. de l'Acad. Roy. de Belg. 1848. Lophopus Bakeri. Van Beneden, Sur les Bryoz. fluv. de Belg., p. 24, pl. 2,
Mém. de l'Acad. Roy. de Belg. (Original figure.) 1849. Lophopus crystallinus. Allman, Rep. Brit. Assoc., Trans. of Sect., p. 72.
Iconography.— The original figures are those of Trembley, Baker, Shaw, Dumortier, and Van Beneden.
Habitat.-In ponds and ditches, where it attaches itself to the submerged parts of Lemna, Sparganium, and various other aquatic plants, avoiding exposure to bright sunlight.
LOCALITIES.— British : Abundant in a millpond near Little Baddow, Essex; a pond in the Zoological Gardens, Dublin; abundant. G. J. A.-In the water by the side of the Willow-walk, Chelsea, and in various waters in the neighbourhood of London. Shaw.
Foreign: Holland. Trembley.-Belgium. Dumortier and Van Beneden.
When removed from the water, L. crystallinus appears immersed in a transparent gelatinous investment which envelopes the entire colony, leaving only the orifices free. This investment, which, as has been already shown,* is really a delicate transparent membrane filled with a fluid and representing the ectocyst, may be easily removed; and, indeed, specimens kept for some time in confinement may often be found quite freed from it. I cannot help thinking that the specimens observed by M. Van Beneden, and described by this naturalist as destitute of the investment in question, were only accidentally in this state, which I believe is never presented by freshly captured, healthy individuals.
* Vide supra, p. 14.
Full-grown specimens have the endocyst deeply lobed, so as to cause it to present a kind of palmate appearance. The intervals of the lobes, however, are nearly filled by the gelatinoid ectocyst. Young specimens are not lobed, and then they correspond to the “Bellflower Animal ” of Baker.
Both Baker and Van Beneden ascribe to this animal a power of locomotion. To the existence of this power, however, my own observations are opposed; the colony is certainly very easily detached, and will when all is quiet again readily fix itself, so that a passive change of place may in this way be effected; but though I have had numerous specimens constantly under my eyes, I have never witnessed anything like the active locomotion of Cristatella.
The ectocyst is perfectly colourless and transparent, the endocyst and polypides are pale brownish-yellow.
The statoblasts are larger than those of any other fresh-water Polyzoon, except Cristatella. They are of an elliptical form, with the long diameter prolonged at each extremity into a short acute point.
L. crystallinus is one of the largest of the Polyzoa, and this circumstance, together with the transparency of the cænæcium, renders it peculiarly well adapted for examining the structure of the class.
In many cases the perigastric space in Lophopus was found to contain numerous spherical bodies (Pl. II, figs. 16–23), which floated freely in the perigastric fluid, where they were rapidly whirled about under the influence of the currents. They varied much in size, some being about the doo of an inch in diameter, while others were as large as an ordinary Volvox globator. Some were seen to consist in a spherical transparent cell, with nearly colourless granular contents, involving numerous minute spherical bodies, apparently young cells; these contents were aggregated on the inner surface of the wall, where they constituted a thick, somewhat irregular layer. In other cases the contents were seen to be entirely resolved into a brood of young cells, which completely filled the parent-cell; while in the largest individuals these secondary cells might themselves be seen in various stages of growth and subdivision, some presenting the appearance of a little spherical granular mass with visible nucleus, but without distinct cell-wall, others somewhat larger, with the cell-wall become distinct, and others in which the granular contents had retired from the cell-wall towards the centre of the cell, where they were to be seen surrounded by a colourless fluid. In a still further stage the contents had become divided into two masses, while in still more advanced cases each of these masses might be seen again dividing into two others, the subdivision being preceded by the appearance of two nuclei in each mass. The whole of this brood of young cells was ultimately liberated by the rupture of the large parent-cell, and then floated away in the perigastric fluid.
That the bodies now described had no necessary connection with the Polyzoon in whose interior they occurred, must, I think, be admitted ; their presence is, without doubt, purely parasitical.