ROTATORY APPARATUS IN BDELLOIDS

All Bdelloid Rotifers have the same body plan: elongated body, ciliate d apical region (rotatory apparatus or corona), telescopically retract able foot and head with pseudosegments, paired gonads, single dorsal a ntenna, apical rostrum, ramate mastax. Bdelloids use the rotatory appa ratus for both locomotion and collecting food and therefore the shape of the corona and arrangement of the cilia, both related to the animal 's life style, probably are important for the fitness of the rotifers. We have analyzed the fine morphology of the corona and the rostrum fr om species belonging to the four families, Habrotrochidae, Philodinida e, Adinetidae and Philodinavidae, each with its own form of feeding an d locomotion. In the rostrum one can distinguish a sensorial area and a ciliated area. The former is common to all bdelloids, while the latt er is lacking in the Adinetidae. Three models of corona can be recogni zed: 1) a simple ciliated field of undifferentiated cilia (Adinetidae) , 2) a well developed ciliated field with specialized cilia forming th e paired trochi on the disks and the cingulum (Habrotrochidae and Phil odinidae), and 3) a ciliated field with a single trochus encompassing rudimentary pedicels and cingulum (Abrochtha). We propose (1) to no lo nger use Digononta as a taxon, (2) to assign the class rank to Bdelloi dea, (3) to distinguish three orders, grouping Philodinidae and Habrot rochidae under a single order and (4) to retain the current families.