Morphology and ontogenesis of two new Hemiholosticha species (Ciliophora, Hypotrichia, Hemiholostichidae nov. fam.).

The morphology and ontogenesis of two new hypotrich ciliates, Hemiholosticha solitaria and Hemiholosticha germanica, were studied using live observation, protargol impregnation, and scanning electron microscopy. Both species share a medium-sized, almost globular body with a short anterior projection; two macronuclear nodules with a single micronucleus in between; a central contractile vacuole; three or four ventral, one postoral, one right and one left marginal cirral row; and three dorsal kineties extending along ribs. However, H. germanica is distinguished from congeners by a higher number of cirri in ventral rows R1 and R2 (3-6 vs. 2 cirri in each row). Hemiholosticha solitaria differs from congeners by having four (vs. three) ventral cirral rows and by the lack (vs. presence) of intracellular green algae. The ontogenesis of H. solitaria follows the H. pantanalensis mode in that (i) the oral primordium develops in a deep pouch and generates the first two cirral streaks in addition to adoral membranelles and undulating membranes, (ii) the undulating membrane anlage does not produce any cirri, and (iii) the longitudinal ventral cirral row R3 originates from two anlagen. The ontogenetic peculiarities along with the 18S rRNA gene phylogenies suggest classification of Hemiholosticha, Psilotrichides, and Urospinula into a new family, Hemiholostichidae.