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 Flosculariaceae the trochus is a horseshoe-shaped ridge deep down in the funnel-shaped disk.
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.
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.
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.
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).
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.).
Asplanchnaceae; trochus circular; foot absent or minute; trophi incudate; stomach blind; males frequent, not very dissimilar to females.