Protocyclidium terricola (Kahl 1931) Foissner, Agatha & Berger 2002

Ciliate, moderately variable in size, usually about 140 x 100 microns but large trophonts occasionally up to 250 microns in length; starved and precystic cells are usually about 80-120 microns long. Shape fairly constant, bean-like, dorsal side markedly convex, ventral side concave at level of bottom of vestibulum, anterior and posterior ends broadly rounded. Right wall of vestibulum semicircular to slightly sigmoid, extends to posterior third of cell. Left wall of vestibulum commences at level of the bottom of vestibulum, extends semicircularly dorsad, to meet cowl-like anterior end. Thus, right wall of vestibulum distinctly longer than left. Right side markedly convex, left side flat to slightly convex, no diagonal groove. Macronucleus elliptical (ratio about 2: 1), usually located in posterior half of body. Nucleolus net-like. Single, elliptical micronucleus attached to macronucleus. Contractile vacuole in posterior third of left side of cell; during diastole surrounded by many smaller collecting vesicles, single excretory. Pellicle soft, flexible. Many subpellicular mucocysts, about 1.5 X 1 microns, arranged in small clusters between somatic kineties, give cells brownish colour at low magnification. Mucocysts become extruded after addition of methyl green-pyronin, form spongy envelope around cell consisting of 5-10 microns long threads. Cytoplasm colourless, in well-nourished cells densely packed with about 1 microns roughly spherical, yellowish crystals and 1-10 microns refractile globules. Many small and large food vacuoles containing few to hundreds of small, colourless flagellates or one to few individuals of various species of ciliates. In starved cultures, cannibalism may even occur. Movement slowly gliding on right side or rotating about main body axis, remains nearly motionless during feeding. Kuehneltiella terricola waits for prey, which is captured in huge vestibulum and then apparently sucked in by strong cytoplasmic cyclosis.

Ciliate with a fairly constant shape. Dorsal side convex, ventral side neatly curved, anteriorly and posteriorly somewhat tapering. Slightly flattened (less than 2:1), curved in ventral view, right side concave, left convex; very similar to some populations of P. alpestris. Macronucleus in centre of cell, slightly ellipsoid, about 5 microns in diameter; nucleoli large, roundish. Micronucleus large compared to macronucleus, lenticular, about 2.5 x 2.5 x 2 microns in vivo. Contractile vacuole at posterior end. Cortex flexible, slightly furrowed on right side by somatic kineties. Extrusomes not recognizable in vivo although many minute, cortical granules impregnate with protargol; show similar arrangement to those of P. alpestris, but are slightly smaller and thus less striking. Cytoplasm colourless, hyaline, in well-fed specimens rather densely packed with 2-5 microns sized food vacuoles which contain only 1-3 bacteria each. As in P. alpestris, 1-2 small vacuoles containing a single, yellowish crystal near posterior end. Movement moderately rapid gliding and rotating about longitudinal axis. Cilia 7 microns long, arranged in 10 slightly spiralling rows. Somatic infraciliature rather similar to that of P. alpestris, especially regarding wide gap between kineties 1 and 2. Kineties 1-4 bear 10-15 ciliated dikinetids each. Kinety 5 has ciliated dikinetids in anterior and single cilia in posterior half. Kineties 6-8 consist of single cilia. Postoral kineties 9 and 10 commence with single, ciliated dikinetid each and continue with single cilia. Kinety 10 markedly shortened; all other kineties terminate slightly before posterior pole which is thus without cilia. Kineties 1-8 form straight, short preoral suture.

Colpodid ciliate, 20-30x 15-20 microns. Broadly reniform to oval, ventral side usually slightly indented preorally, dorsal side almost semicircular, both ends broadly rounded. Flattened approximately 2:1, right side flat, left more or less convex. Macronucleus and micronucleus spherical to slightly ellipsoid, left of median between paroral membrane and contractile vacuole. Macronucleus with conspicuous, central nucleolus. Single micronucleus which does not impregnate with protargol. Excretory pore of contractile vacuole at apex of posterior pole. Cytopyge on dorsal side between posterior thirds of somatic kineties 5 and 6, marked by argyrophilic line extending to excretory pore of contractile vacuole. Cortex thin, bright, distinctly furrowed and crenulated by somatic kineties. Many discoid cortical structures (mucocysts?) which usually impregnate heavily with protargol. Cytoplasm colourless, often appearing greenish due to many about 3 microns sized food vacuoles containing bacteria and vacuoles with crystalline inclusions. Movement very slow, remarkably clumsy. Division in reproductive cysts. Cilia paired, about 7 microns long, widely spaced except in anterior thirds of kineties 1 and 2. Usually 10, rarely 11 curved and posteriorly slightly shortened somatic kineties. 3 of these commence postorally others abut along distinct preoral suture. Posterior half of kinety 2 slightly shifted to left. Oral aperture ventro-lateral slightly above mid-body, elliptical, somewhat inclined to longitudinal axis of cell. Vestibulum gradually deepening from distal to proximal. Paroral membrane completely covered by right and proximal vestibular wall, thus not recognizable in specimens prepared with the dry silver nitrate method. Very fine fibres, which form a curtain-like structure and originate from paroral dikinetids. 4-5 adoral organelles on left slope of vestibulum, become gradually larger and wider from distal to proximal and thus form triangular ribbon; proximal organelles often indistinctly separated from each other.

Ciliate, about 150-200 x 60-100 microns. Approximately 60 somatic kineties consisting postorally of single cilia. 21 adoral organelles on average, 6-8 of which insert along the vestibular slope. Anterior end broadly curved, postorally usually convex and narrowing, posterior extremity narrowly rounded. Preoral rostrum bluntly pointed. Laterally evenly flattened approximately 2:1. Rather stiff and not contractile. Macronucleus near centre of cell and about 35 microns in diameter, shrinks considerably during preparation; in protargol slides surrounded by alveolated coat containing single micronucleus; nucleolus reticulate. Contractile vacuole at posterior end, with short, anteriorly projecting collecting canal at left; excretory pore on right side near posterior pole. Cortex deeply furrowed by somatic kineties. Cytoplasm colourless, conspicuously vacuolated. Well-fed specimens contain many 10-15 microns sized food vacuoles with spongious or compact content. Movement moderately rapid gliding, without peculiarities. Somatic kineties course slightly spirally posteriad. Several shortened postoral kineties form more or less pronounced median suture in posterior third of right and left side. As in the other species an argyrophilic line, probably the LKm fibre, right of kineties. Ciliature slightly condensed near adoral organelles, loosen up in posterior third. All somatic kineties consist of slightly inclined dikinetids; in anterior third of cell both basal bodies have about 10 microns long cilia, whereas postorally only one basal body of each dikinetid is ciliated. Oral aperture in anterior 1/6-1/7 of cell (distance anterior end to proximal oral margin in protagol impregnated cells 20-26 microns, strikingly small (about 10 x 6 microns) compared to size of cell, only slightly depressed. Paroral membrane semicircular, consists of 20-30 dikinetids. Adoral zone of organelles distinctly sigmoid e to dorsal side. Organelles along vestibular slope consist of 2 long kineties (5 basal bodies each) and 1 short row (2-3 basal bodies), whereas those in preoral suture consist only of 2 kineties with 4-6 basal bodies each.

Length 2.5-4 microns. Cell outline roundish to ovate, D-shaped, compressed laterally, about one fifth as thick as long. Two heterodynamic flagella inserted subapically at an angle of about 70 degrees -90 degrees to anterior end of cell. Flagella taper at tips. Anterior flagellum approximately of cell length or slightly shorter, posterior flagellum 1.5 to 2.0 times cell length, trails. Cell truncate in profile, with depression where flagella leave cell. Flagella emerge from a broad pocket, which originates near centre of cell. Cell, in particular the area surrounding flagellar pocket, rich in granules, possibly extrusomes. Nucleus ventral, close to flagellar pocket. Contractile vacuole dorsal. Cells appear to be surrounded by mucilage; sometimes covered with adhering particles. Dividing cells with two trailing and one or two anterior flagella often observed. Cells glide in a wobbling manner, much like Heteromita globosa; posterior flagellum trails, anterior flagellum moves across substrate in front of cell, beat envelope covers an angle of about 150 degrees. Ingestion of bacteria seen in several cases. When anterior flagellum makes contact with a bacterium, the prey is moved towards the cell by the flagellum and taken up in the flagellar pocket just anterior to the site where the flagellum leaves the pocket.

Colpodid ciliate, 25-35 x 10-15 microns. Shape very distinctive, with posterior two thirds cylindrical, anterior third usually bluntly pointed and projecting ventrally, posterior end usually broadly, rarely narrowly, rounded. Moderately flattened, wedge-shaped in ventral and dorsal view. Macronucleus spherical to slightly ellipsoid, usually in posterior half of cell, more rarely in centre; nucleoli large but not very compact, hence indistinct. Micronucleus conspicuously large, 4 x 2 microns, comma-shaped, attached to macronucleus. Contractile vacuole at posterior end; at left posterior end hyphen-like, argyrophilic structure, presumably the cytopyge. Cortex deeply furrowed by somatic kineties, especially in anterior half, giving live cells twisted appearance; rope-like furrowing disappears almost entirely in silver preparations. Cortex slightly nodulated by about 1 microns sized globules, presumably extrusomes, which are refractile and arranged in indistinct rows between somatic kineties. Cytoplasm colourless, contains several up to 5 microns sized, apparently empty vacuoles and few 1-5 microns sized yellowish, rhomboid to hook-shaped crystals. Food not known, presumably bacteria. Movement slow by rotation about longitudinal axis. Cilia paired, rather widely spaced, especially in postoral portion of cell. Somatic kineties distinctly spiralling, commence at anterior pole, except for 3 shortened postoral kineties. First kinety right of oral apparatus commences in the posterior half of the cell. Oral apparatus small, on ventral side of projecting anterior end; aperture triangular, opening directed anteriorly as in Cyrtolophosis. Paroral membrane on right slope of vestibulum, continues as normal somatic kinety postorally; 2-4 argyrophilic, unpaired granules (basal bodies?), recognizable only after protargol impregnation, between paroral membrane and postoral tail. Adoral organelles arranged like an inverted letter V, composed of zigzag ordered, ciliated basal bodies. Paroral membrane and left adoral organelle at same level on anterior vestibular slope forming archway over right organelle, which inserts obliquely on bottom of shallow vestibular trough; cilia of right adoral organelle always posteriorly inclined in protargol impregnated cells. Pharyngeal fibres very short and fine.