- Three stages in the development of Trochus, during the process of torsion.
This typically consists of two concentric zones, the trochus and cingulum, often separated by a groove or gutter which may be finely ciliated; but in several genera of no close affinity, where it is very oblique to the longitudinal axis of the body, it is represented by a general ciliation of the surface (Taphrocampa, Rattulus, Copeus, Adineta).
2, I) and its allies, the trochus being oval with two median gaps, the cingulum, more delicate, and complete.
Conifera; the star represents the ciliated cup connected by ciliated depressions with the groove; 5, disk of Conochilus, like the Bdelloid, but with mouth antero-dorsal, the gap postero-ventral; 6, disk of Stephanoceroscingulum broken up into setiferous lobes, groove a naked funnel, trochus a horseshoe-shaped ridge, mouth central.
(B) Ploimaeae; disk variable, often circular, sometimes with a lobed trochus bearing membranelles (vibratile styles); trophi complete, malleate, submalleate, virgate, or forcipate; anus subapical; foot usually short, and usually bearing two toes which may be much elongated.
Trochus, shell umbilicated, spire pointed and prominent, British.
- Diagrammatic Views of Disks of Rotifers: cingulum continuous; trochus dotted; groove shaded; mouth black.
In most rotifers, on the contrary, the trochus is stronger than the cingulum, often lobed, and with some of its cilia aggregated into vibratile styles homologous with the combplates of Ctenophora (q.v.) and the membranelles of ciliate Infusoria (q.v.).
The trochus forms the powerful currents for locomotion, and for the supply of food material, while the cingulum produces a local current round the upper rim of the corona to bring the food particles direct to the mouth, which is displaced through a postero-ventral gap in the trochus to lie behind the disk, just as occurs in the more specialized Ciliata.
There is a dorsal interruption to the disk, in volving both trochus and cingulum and groove in this case the two halves of the disk may be developed in lobes, flower-shaped in Melicerta ringens, but often rounded and projecting like kettledrums. These give a strong impression of two crown wheels revolving in the same sense.
In most Ploima the dorsal gap is not well marked, and the trochus is broken up into a number of lobes, often furnished with vibratile styles, in front and at the sides, but ventrally passing into the uniformly ciliated oral funnel.
C, ventral view: x', trochus; x, cingulum; other letters as above.
Ment and of the struc ture of the disk to their identification of "trochus" and "cingulum" with the preoral and postoral wreaths of the trochophore larva.
Asplanchnaceae; trochus circular; foot absent or minute; trophi incudate; stomach blind; males frequent, not very dissimilar to females.
Trochus a pair of ridges or horseshoe open in front.
In Flosculariaceae the trochus is a horseshoe-shaped ridge deep down in the funnel-shaped disk.
The current formed by the trochus is a gigantic vortex-ring, the down stroke of the cilia being directly outwards, brit the wave beats running round the organ in uniform succession in one direc tion.