All Bdelloid Rotifers have the same body plan: elongated body, ciliated apical region (rotatory apparatus or corona), telescopically retractable foot and head with pseudosegments, paired gonads, single dorsal antenna, apical rostrum, ramate mastax. Bdelloids use the rotatory apparatus 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 from species belonging to the four families, Habrotrochidae, Philodinidae, Adinetidae and Philodinavidae, each with its own form of feeding and locomotion. In the rostrum one can distinguish a sensorial area and a ciliated area. The former is common to all bdelloids, while the latter is lacking in the Adinetidae. Three models of corona can be recognized: 1) a simple ciliated field of undifferentiated cilia (Adinetidae), 2) a well developed ciliated field with specialized cilia forming the paired trochi on the disks and the cingulum (Habrotrochidae and Philodinidae), and 3) a ciliated field with a single trochus encompassing rudimentary pedicels and cingulum (Abrochtha). We propose (1) to no longer use Digononta as a taxon, (2) to assign the class rank to Bdelloidea, (3) to distinguish three orders, grouping Philodinidae and Habrotrochidae under a single order and (4) to retain the current families.
rotatory apparatus rostrum Rotifera Bdelloidea SEM systematics