Gymnostomata

Subclass (1) Gymnostomata Bütschli, 1889

Syns. Gymnostomatida-Rhabdophorina s.l.,
Gymnostomorida p.p.,
Homotricha p.p.

Cytostome, at or near body surface, located apically, subapically, or laterally. Limited oral ciliation, but often uniform holotrichous somatic ciliation. Cytopharyngeal apparatus of rhabdos type. Toxicysts common. Single nucleus (one very small group), micro- and macronucleus both diploid (one major group of psammophilic forms), and macronucleus oligoploid (rarely) or highly polyploid (rest of the groups). Body size often large, and many species carnivorous.

Homokaryotic forms (two or more nuclei, but all allegedly diploid with RNA-rich nucleolus); small body size; cytostome apical, slit-like, partially encircled by cytoplasmic protuberances; body convex dorsally; cilia principally on ventral surface; marine benthic organisms, mainly algivorous. Order 1. PRIMOCILIATIDA Corliss, 1974

Dual nuclear apparatus, but macronuclei diploid, nondividing; fragile, highly thigmotactic, often elongate; oral area apical or ventral; contractile vacuolar system often, anparently, absent; obligate interstitial forms, all marine, except one genus. Order 2. KARYORELICTIDA Corliss, 1974

With characteristics of subclass s.s. (above). Cytostome apical or subapical; circumoral infraciliature unspecialized; macronucleus polyploid; species widely distributed. Order 3. PROSTOMATIDA Schewiakoff, 1896

Cytostome apical or subapical, oval or slit-like, sometimes not permanently open; cytopharynx eversible in some species; coronal ciliature and field of clavate "sensory" cilia often present; toxicysts localized, typically in or near oral area; rhabdos complex; kinetodesmata reported; rapacious carnivores, some equipped with proboscis and a few with (nonsuctorial) tentacles. Order 4. HAPTORIDA Corliss, 1974

Cytostome vent- or slit-like, along edge (ventral surface?) of laterally compressed body, with nearby ciliature showing left-right differentiation; macronuclei possibly of low ploidy number; often large (sometimes with lengthy, attenuated anterior end), voracious carnivores, widely distributed and facultatively interstitial. Order 5. PLEUROSTOMATIDA Schewiakoff, 1896

Homokaryotic forms (two or more nuclei, but all allegedly diploid with RNA-rich nucleolus); small body size; cytostome apical, slit-like, partially encircled by cytoplasmic protuberances; body convex dorsally; cilia principally on ventral surface; marine benthic organisms, mainly algivorous.	*Order 1. PRIMOCILIATIDA* Corliss, 1974**
Dual nuclear apparatus, but macronuclei diploid, nondividing; fragile, highly thigmotactic, often elongate; oral area apical or ventral; contractile vacuolar system often, anparently, absent; obligate interstitial forms, all marine, except one genus.	*Order 2. KARYORELICTIDA* Corliss, 1974**
With characteristics of subclass s.s. (above). Cytostome apical or subapical; circumoral infraciliature unspecialized; macronucleus polyploid; species widely distributed.	*Order 3. PROSTOMATIDA* Schewiakoff, 1896**
Cytostome apical or subapical, oval or slit-like, sometimes not permanently open; cytopharynx eversible in some species; coronal ciliature and field of clavate "sensory" cilia often present; toxicysts localized, typically in or near oral area; rhabdos complex; kinetodesmata reported; rapacious carnivores, some equipped with proboscis and a few with (nonsuctorial) tentacles.	*Order 4. HAPTORIDA* Corliss, 1974**
Cytostome vent- or slit-like, along edge (ventral surface?) of laterally compressed body, with nearby ciliature showing left-right differentiation; macronuclei possibly of low ploidy number; often large (sometimes with lengthy, attenuated anterior end), voracious carnivores, widely distributed and facultatively interstitial.	*Order 5. PLEUROSTOMATIDA* Schewiakoff, 1896**