Order 3. ASTOMATIDA Schewiakoff, 1896

Syns.

Anoplophryida, Anoplophryin[e]a, Anoplophrymorphida, Astomat[e]a, Astom[at]ina, Haptophryina, Hoplitophryina

Body relatively large, especially often lengthy, cylindrical or flattened-ovoid, uniformly ciliated, mouthless; an infraciliary endoskeleton of considerable complexiry may be present, frequently with elaborate holdfast organelle at anterior end of body; typically anisotomic fission, sometimes involving budding with chain-formation; contractile vacuoles present, in one or two rows, but cytoproct absent; universally endosymbiotic (possibly one exception: see first family, below), with majority found in digestive tract of oligochaete annelids from soil, fresh-water, brackish, or marine habitats; but some species in polychaetes, leeches, turbellarians, or molluscs, and one major group exclusively in tailed amphibians.

Mouthless, medium large, ovoid, with holotrichous ciliation, mucocysts, lengthy macronucleus, multiple micronuclei, and scattered contractile vacuoles; but no endoskeleton, no thigmotactic cilia, and found entirely free-living; special feature: prominent, centrally located, regularly pulsating ("contractile"?) central vacuole; taken from a eutrophic pool in the Austrian Alps.	Family ARCHIASTOMATIDAE Foissner, 1976
No endoskeleton, apical hooks, or suckers, but area of thigmotactic cilia often present; reproduction without chain formation; body relatively small, ovoid to elongate-ovoid; primarily in terrestrial oligochaetes, though some species presumably from other hosts (e.g., the dubious Orchitophrya was found in sea-star gonads and an Anoplophrya reported	Family ANOPLOPHRYIDAE Cépède, 1910
With general characteristics of the Anoplophryidae (above), but with differences in the silverline system (kinetal patterns, "systèmes sécants," thigmotactic area, etc.) which especially set its genera apart; ciliature may be spiraled; macronucleus rod-like or dendritic; reproduction palintomic; in polychaete annelids.	Family BUETSCHLIELLIDAE de Puytorac, n. fam.
Body elongate, cylindrical, tapered posteriorly; ectoplasm thickened at apical end, with insertion of some cytoskeletal fibers; body ciliation moderate to light; generally single row of contractile vacuoles; chain formation common in division; commensals of only fresh-water aquatic oligochaetes except for a few species in an occasional terrestrial annelid.	Family HOPLITOPHRYIDAE Cheissin, 1930
Body generally ovoid and flattened, occasionally elongate; apical and dominated by prominent inverted "V"-shaped cytoskeletal organelle onto which numerous fibers converge; hooks or spines or other attachment fixtures often present; body ciliation dense; one or two rows of contractile vacuoles; chain formation not common; commensals of aquatic and terrestrial oligochaetes, a few polychaetes, and occasionally a fresh-water lamellibranch mollusc.	Family RADIOPHRYIDAE de Puytorac, 1972
Body elongate-ellipsoidal; skeletal fibers little developed; circular area at apical end of body free of cilia; a single median (or two pair of) cytoskeletal hook(s); only two contractile vacuoles; in tropical earthworms.	Family CONTOPHRYIDAE de Puytorac, 1972
Body cylindrical, rounded at both ends; skeletal fibers relatively short; small anterior spine, fixed or mobile; division equal	Family MAUPASELLIDAE Cépède, 1910
Body cylindrical, elongate; rather elaborate cytoskeletal "annulus" at anterior end; body ciliation dense, with kineties often loosely spiraled; division involves chain-formation; in aquatic oligochaetes.	Family INTOSHELLINIDAE Cépède, 1910
Body large, elongate (up to 2,000 µm in length, some species), densely ciliated; kineties converge anteriorly onto horseshoe-shaped suture line; conspicuous adhesive sucker at apical end of body, sometimes provided with two or more hooks or spines; long canal replaces row(s) of contractile vacuoles; anisotomic fission, with chain-formation common; hosts include marine and fresh-water turbellarians, anuran, and (especially) urodelean amphibians.	Family HAPTOPHRYIDAE Cépède, 1923
Body comma-shaped or broadly ellipsoidal in form, flattened, and not especially elongate; thigmotactic area present at anterior end but weakly developed and without well-defined sucker; infraciliary pattern differs from that of the Haptophryidae; scattered contractile vacuoles; two species are commensals in the body caviry of certain land snails, with a third described from African earthworms.	Family CLAUSILOCOLIDAE de Puytorac, n. fam.