Order 1. SYNHYMENIIDA de Puytorac et al., 1974

For	Synhymenida
Syns.	Nassulopsina, Scaphidiodontina, Synhymen[i]ina

Hypostomial frange extensive, winding around anterior part of body; bipolar kineties; body cylindrical, with holotrichous ciliation; no atrium; stomatogenesis parakinetal-like; free-living, predominantly fresh-water forms, though some marine and a number interstitial.

Body generally large but elongate and radially symmetrical; multiple parts to hypostomial frange, encircling much of anterior fifth of body just below level of the cytostome-cytopharyngeal apparatus and separate from preoral suture line; row of 4-5 medially located contractile vacuole pores down ventral surface; macronucleus elongate; quite widely found in fresh-water, oceasionally edaphic, habitats, with one or two species marine.	Family NASSULOPSIDAE Deroux, 1979
Body roughly ovoid, with asymmetrical lobe or beak to the left; one uncertain species very elongate with narrow, pointed tail; single lengthy "membrane," coursing across ventral surface just below oral area and turning anteriad out into the beak along the preoral suture line; predominantly in fresh-water habitats.	Family ORTHODONELLIDAE Jankowski, 1968
Broad anterior end, with body gently tapered posteriorly; hypostomial frange similar to that of the Orthodonellidae (above), but simpler and less conspicuous; mostly marine forms.	Family SCAPHIDIODONTIDAE Deroux, n. fam.