Fam. 5. Philodinidae: Philodina E. (Fig. 110), Rotifer Schrank, Actinurus E., Callidina E. (Fig. 109), Adineta H.
This group is remarkable for the great resisting powers of its members to drought and to heat and cold when dried, a fact which may explain the absence of males, though Janson records the occurrence of winter eggs in four species of Callidina and in Adineta vaga. The body is often strongly pigmented; red in Philodina roseola, Callidina scarlatina, and C. russeola, yellow in P. citrina, Rotifer citrinus, and Discopus synaptae. Most of the species are dust- or moss-dwellers; some, such as Rotifer vulgaris, are equally common in organic débris in infusions, pools, and ditches. Discopus adheres to the skin of the Holothurian Synapta.
Order IV. Asplanchnaceae.—Females ovoid, footless except in Asplanchnopus. Disc often bearing a pair of antennae; circular, often prolonged at the margin into two rounded lobes, interrupted dorsally, depressed at the ventral side into a deep ventral funnel. Trophi incudate (virgate in Ascomorpha), mastax enlarged dorsally into a wide crop; stomach large, blind. Kidneys large, with a "recurrent duct" and numerous tags; bladder large. Brain large, with a median eye, and frequently paired smaller eyes at the base of the marginal processes of the disc; anterior antennae paired, relatively far back on dorsal surface. Males (Fig. 107, 5) relatively large, frequently found.
Fam. 6. Asplanchnidae: Asplanchna G., Asplanchnopus De Guerne, (?) Ascomorpha, Perty, (?) Dinops Western.
Order V. Scirtopoda.—Females of conical shape, with the body prolonged into hollow limb-like expansions (see p. [201]) moved by strong muscles, and ending in branched setose fins like the limbs of Crustacea. Disc as in Bdelloids, but not retractile. Foot represented by two subventral toes, ciliated, inconstant or absent. Trophi malleoramate. Eyes two, latero-ventral, on the disc. Male (Fig. 107, 8) conical, with simple setae.
Fam. 7. Pedalionidae: Pedalion H. (Fig. 117),[[272]] Hexarthra Schmarda.[[273]]
Order VI. Ploima.—Free-swimming forms, more rarely parasites, often adherent by their trophi to a host. Disc variable, often bearing within the cingulum a number of lobes fringed with coarse compound cilia. Foot rarely absent, marked off by a sharp constriction. Mastax variable, rarely malleoramate, never incudate or uncinate. Intestine not blind. Males small.[[274]]
Sub-Order A. Illoricata.—Ploima with a soft flexible integument; disc variable; ciliated auricles sometimes present (Synchaetidae, Notommatidae); foot rarely absent; trophi usually malleate.
Fam. 8. Microcodonidae: Microcodon E., Microcodides Bergendal.
Fam. 9. Rhinopidae: Rhinops H.