Apofrontonia
Apofrontonia Foissner & Song, 2002 (ref. ID; 4528 original paper)
Order Hymenostomatida Delage & Herouard, 1896: Family Frontoniidae Kahl, 1926 (ref. ID; 4528)
[ref. ID; 4528]
We classify Apofrontonia into the family Frontoniidae because it has: (1) three similarly-structured peniculi (no quadrulus like Paramecium, Stokesia and Neobursaridium); (2) basically frontoniid vestibular kineties (lacking in Lembadion, Urocentrum, Paramecium, Neobursaridium); and (3) a pyriform vestibular opening more similar to the triangular one of Frontonia than to the bursiform or oral vestibular opening of Paramecium, Neobursaridium, Stokesia, Lembadion, and Urocentrum: See Corliss (1979), Didier & Puytorac (1994), Foissner et al. (1994, 1999), and Kahl (1931) for figures of the genera mentioned. Possibly, Frontonia or the planktonic Marituja are the closest relatives of Apofrontonia. The former is indicated by body shape, the location of the oral apparatus, and the general somatic ciliary pattern with the distinct preoral and postoral suture; the latter by the vestibular kineties, which cover the vestibular wall, while they are at the right margin of the vestibular opening in most other peniculines, especially Frontonia. (ref. ID; 4528)
Diagnosis; Frontoniidae with large oral apparatus occupying at least half of ventral side. Vestibular cavity with pyriform opening, bowl-shaped and posteriorly gradually merging into cell surface, completely exposing three similarly-structured, comparatively large peniculi; right vestibular wall sigmoidal, covered by numerous (>6) vestibular kineties not extending beyond oral cavity. (ref. ID; 4528)
Remarks; Apofrontonia lametschwandtneri and A. obtusa both have an extraordinarily large oral apparatus, separating them from most peniculines, except Lembadion and Neobursaridium, both quite distinct and only distantly related (no vestibular kineties etc.). However, the main generic feature of Apofrontonia is the pyriform or key-hole-shaped vestibular opening not found in any other genus of the order. The generic feature "vestibular cavity bowl-shaped, completely exposing three similarly-structured peniculi" has been introduced specifically for separating Apofrontonia from Frontonia and Disematostoma. In both of the latter genera, the posterior portion of the peniculi cannot be seen because it is covered by a triangular postoral field (posterior vertex of the oral opening) bearing several short (postoral) kineties abutting to the postoral suture. Such a postoral field is definitely lacking in Apofrontonia, and thus the distal portion of the peniculi is exposed to the observer. The next feature "right vestibular margin sigmoidal and covered by many (>6) vestibular kineties not extending beyond oral cavity" also separates Apofrontonia clearly from Frontonia and Disematostoma. In Frontonia and Disematostoma, there are fewer than six vestibular kineties, and these extend postorally to abut on the postoral suture. Disematostoma, further, has a very long postoral suture extending to mid-body of dorsal side, where it abuts to the excretory pore of the contractile vacuole (Tuffrau & Savoie 1961; Serrano et al, 1990). (ref. ID; 4528)
Etymology; Composite of apo (derived from) and the generic name Frontonia. Feminine gender. (ref. ID; 4528)
Type species; Apofrontonia lametschwandtneri nov. spec. (ref. ID; 4528)
- Apofrontonia lametschwandtneri Foissner & Song, 2002 (ref. ID; 4528 original paper)
Diagnosis
Large Apofrontonia with an average size of 180x120 um in vivo. Obovate and dorsoventrally flattened up to 2:1. Macronucleus rod-like. About 30 scattered contractile vacuoles. Extrusomes fusiform and about 6 um long. Approximately 155 somatic ciliary rows. Vestibulum 2/3 of body length on average; right wall with an average of 13 vestibular kineties. Peniculus 1 composed of about thirteen, peniculus 2 of about ten, and peniculus 3 of about 4 ciliary rows. (ref. ID; 4528)
Descriptions
Cells conspicuous because of large size, look like hollowed eggs due to the large and deep vestibular cavity. Size rather stable, viz., 160-200x105-140 um in vivo, usually near 180x120 um; more variable in silver slides, viz. 167-215x115-180 um, on average 183x145 um; length:width ratio 1.3-1.6, on average 1.5 in vivo and 1.3 in silver nitrate preparations. Shape basically obovate and considerably asymmetrical since more or less flattened right laterally and ventrally and distinctly vaulted dorsally, where thickness gradually increases from anterior to posterior, an unusual pattern. Anterior end almost invariably more broadly rounded than posterior, smoothly rounded or slightly tapering, especially in silver slides; posterior end often slightly indented where postoral suture extends. Shape rather sensitive, becomes roundish in disturbed and preserved specimens. Macronucleus not in fixed position, rod-like and often rather tortuous, with a definite deep constriction in about 5% of specimens; one end often slightly inflated; contains many long fibres visible by interference contrast optics. Micronucleus not observed. About 30 contractile vacuoles scattered beneath body surface, each with one, rarely two excretory pores between ciliary rows; without collecting canals. Cortex composed of ordinary peniculine "units" easily recognizable with interference contrast optics; units less distinct dorsally, where the longitudinal ridges are more conspicuous than the transverse ones; after silver nitrate impregnation, three cortical patterns can be observed: (i) quadrangular cortical meshes similar to those seen in vivo and, for instance, also in Frontonia and Paramecium (Roque 1961; Dragesco & Dragesco-Kerneis 1986; Foissner et al. 1994, 1999; Petz et al. 1995); (ii) irregular, short transverse silverlines connecting neighbouring kineties, similar to those sometimes seen in Paramecium (Gelei 1937); and (iii) no pattern, likely due to insufficient impregnation. Extrusomes numerous, very regularly arranged possibly right of and within ciliary rows, that is, alternate with cilia, do not form distinct fringe because small compared to size of cell; fusiform, about 6x0.7 um in size, become up to 25 um long, slightly curved rods when extruded. Cytoplasm colourless, does not contain pigment granules or a granule spot (as some Frontonia species do), cells however dark at low magnification (< /_ x100) because large and usually packed with food vacuoles, many lipid droplets up to 10 um across, and some 1-3 um-sized crystals. Feeds on bacteria, coccal cyanobacteria and medium-sized ciliates, such as Colpoda magna and Nassula spp., digested in food vacuoles up to 30 um across; the latter may make cells colourful due to the food vacuoles containing cyanobacteria in various stages of digestion. When undisturbed, cells remain almost motionless collecting food, and can thus be easily photographed; when disturbed, they glide and swim rather quickly by rotation about main body axis. Somatic cilia about 15 um long in vivo, arranged in approximately 155 closely spaced rows. Ciliary pattern basically as in Frontonia (Dragesco & Dragesco-Kerneis 1986; Foissner et al. 1994); that is, with a distinct preoral and postoral suture, both rather short and not extending onto dorsal side, anterior suture more conspicuous than posterior one because wider and first cortical unit of left side ciliary rows unciliated. Ciliary rows extend meridionally, those of ventral side abut to the sutures, except the vestibular kineties and about 10 postoral kineties gradually shortening from anterior to posterior along left mouth margin. Details of kinetids as in other peniculines, especially Frontonia (Roque 1961; Gil & Perez-Silva 1964; Didier 1971; Dragesco & Dragesco-Kerneis 1986). Briefly, cilia appear single in scanning electron micrographs and silver carbonate preparations, where each cortical unit contains a single, distinct granule, likely a basal body, associated with a kinetodesmal fibre extending anteriorly at the right side of the kinety; sometimes, a faintly impregnated second granule is recognizable anterior of the strongly impregnated one; in vivo, the cortical units contain two granules, while usually even three granules forming conspicuous triangles are recognizable in silver nitrate preparations; the rightmost granule of the triangles often appears ring-like and slightly larger, suggesting that is a parasomal sac or extrusome. Further, there is a minute ring (in vivo) or a granule (in silver nitrate preparation) between each two kinetids of a row; likely, this is an attachment site of a trichocyst. Oral opening very large, occupying two thirds of body length and, at widest site, almost one third of body width on average, distance to anterior body end slightly shorter than to posterior; left margin convex and sharply defined, right gradually merging into body proper and sigmoidal, producing a highly characteristic pyriform or key-hole-shaped vestibular outline. Vestibular cavity deepest in anterior third, where it extends to mid of body, flattens in posterior half to gradually merge into cell surface at posterior mouth margin; fragile, that is, often flattens or even bursts in preparations. Left vestibular wall convex, covered by three conspicuous peniculi: peniculus 1 as long as vestibulum, slightly narrowed anteriorly and posteriorly, where kineties shorten along left margin, composed of about 13 rows of very regularly and densely spaced, approximately 20 um long cilia; peniculus 2 close to peniculus 1, slightly cuneate, that is, widest anteriorly and slightly shorter than peniculus 1, composed of about 10 rows of very regularly and densely spaced, approximately 20 um long cilia; peniculus 3 distinctly separate from peniculi 1 and 2, sigmoidal, posteriorly 20% shorter than peniculi 1 and 2, composed of only 4-5 rows of densely spaced, 5-10 um long cilia forming many closely spaced short, oblique rows. Right vestibular wall flabby, sigmoidal both in outline an surface view, covered by an average of 13 kineties, hardly recognizable if cells are viewed ventrally, but forming a conspicuous stripe in specimens viewed slightly laterally; in preparations, the vestibular cavity and its right wall flatten, exposing the vestibular kinety stripe to the observer even if cells are viewed ventrally. Vestibular kineties as long as vestibular opening, do not extend posteriorly as in Frontonia, anteriorly gradually slightly shortened from left to right, while posteriorly distinctly shortened from right to left, composed of very closely spaced dikinetids zigzagging in posterior two thirds of rows. Paroral membrane at left (proximal) margin of vestibular kinety stripe and thus distinctly shortened posteriorly, composed of very closely spaced, zigzagging dikinetids associated with fine fibres impregnating with silver nitrate and extending to the cytostomial slit. Cytostomial slit in mid vestibulum, sigmoidal, about as long as peniculus 3, and thus not extending to posterior end of vestibulum. There is a complicated fibre system associated with the oral structures. (ref. ID; 4528)
Remarks
Apofrontonia lametschwandtneri has a very distinct identity due to the huge oral apparatus and the scattered contractile vacuoles. This combination of features separates it from all described peniculine species, except the Frontonia obtusa discovered by Song and Wilbert (1989) in pond in Germany. Frontonia obtusa has the same generic features as A. lametschwandtneri and is thus transferred to that genus: Apofrontonia obtusa (Song & Wilbert, 1989) nov. comb. Apofrontonia obtusa differs from A. lametschwandtneri by the following features: body size (80 vs. 180 um), number of somatic (90 vs. 170) and vestibular kineties (9 vs. 13), number of kineties in the peniculi (about 1/3 higher in A. lametschwandtneri), and number (4-5 vs. about 30) and location (laterally vs. scattered) of the contractile vacuoles. (ref. ID; 4528)
Dedication
We dedicate this species to Prof. Dr. Mag. Alois Lametschwandtner, an honest colleague and head of the Zoology Institute of Salzburg University. (ref. ID; 4528)
Type locality
Saline soil from flooded grassland in the Maracay National Park, north coast of Venezuela, W 68 degrees, N 10 degrees. (ref. ID; 4528)
Type specimens
1 holotype slide and 4 paratype slides of silver nitrate-impregnated specimens have been deposited in the Biology Center of the Museum of Upper Austria, Linz (LI), Austria. Relevant cells are marked by a black ink circle on the cover glass. (ref. ID; 4528)