Drepanomonas minuta Foissner & Omar, 2014

Omar, Atef & Foissner, Wilhelm, 2014, Three New Microthoracids (Ciliophora, Nassophorea) from Austria and Venezuela, Acta Protozoologica 53 (4), pp. 295-311 : 296-297

Drepanomonas minuta Foissner & Omar nov. spec.

( Figs 1–6 , 9–15 ; Table 1)

Diagnosis: Size in vivo about 22 × 11 µm. Body semi-ellipsoidal with tapered anterior and rounded posterior end, dorsal margin convex, ventral straight. Cortex flat, crenellated along somatic kineties. Two extrusomes, one in anterior dorsal half, the other subterminally in ventral side. Somatic kinety 4 commences with three dikinetids and one monokinetid, followed by a wide break in mid-body and three monokinetids posteriorly. Kineties 6 and 7 partially and fully non-ciliated, respectively. Left portion of postoral complex with three narrowly spaced monokinetids and a single monokinetid far posteriorly. On average a total of 85 basal bodies. Oral apparatus slightly posterior to mid-body.

Type locality: Upper soil layer from a mixed forest in the surroundings (Neuhaus area) of the town of Salzburg, Austria, 47°48′N, 13°04′E .

Type material: One holotype and nine paratype slides with protargol- and silver nitrate-impregnated specimens have been deposited in the Biology Centre of the Museum of Upper Austria, Linz (LI). The holotype and important paratype specimens have been marked by black ink circles on the coverslip .

Etymology: The Latin adjective minuta (small) emphasizes the small size of the species.

Description: Size in vivo 18–25 × 8–13 µm, usually about 22 × 11 µm, as calculated from some in vivo measurements and values shown in Table 1, assuming 15% preparation shrinkage. Body semi-ellipsoidal to slenderly semi-ellipsoidal with a length: width ratio of 1.8–2.5:1 and an average of 2.1:1; dorsal side distinctly convex, ventral straight; anterior end tapered, posterior rounded, cells thus slightly wider posteriorly than anteriorly; flattened laterally up to 2:1 and lenticular in ventral and dorsal view ( Table 1; Figs 1–6 , 9–15 ). Nuclear apparatus anterior to mid-body. Macronucleus globular to broadly ellipsoidal, contains some globular masses, probably nucleoli up to 1 µm across. Micronucleus globular, near or attached to ventral side of macronucleus ( Table 1; Figs 1, 6 , 9–12 ). Contractile vacuole in third quarter of body, slightly posterior and dorsal of buccal cavity, excretory tube difficult to see ( Table 1; Fig. 1 ). Cytopyge posterior and slightly left of contractile vacuole, usually forms a blister containing food remnants; in silver nitrate preparations, represented by a thick, short silverline right of left portion of postoral complex ( Figs 1 , 14 ). Extrusomes lenticular, about 4 × 1 µm in size, only one extrusome each in anterior and posterior portion of body: anterior extrusome present in only few specimens, slightly anterior and dorsal of macronucleus; posterior extrusome recognizable in most specimens in vivo, invariably in subterminal ventral side posterior to cytopyge, occasionally impregnated with protargol ( Figs 1 , 12, 13 ). Cytoplasm hyaline, contains some lipid droplets about 1 µm across. Glides rapidly interrupted by short jerks.

Cortex rigid and glossy, smooth except for a distinct crenellation left of somatic kineties ( Figs 1, 2 ). Details of ventral side organized as follows: preoral kineties in distinct furrows; oral opening slightly posterior to mid-body; posterior to oral apparatus a short concavity containing cytopyge and the single cilium of the right portion of the postoral complex ( Figs 1, 4, 5 , 9, 11, 14 ). Silverline pattern as described in D. hymenofera by Omar and Foissner (2013), i.e., cortex studded with minute, argyrophilic granules ( Figs 14, 15 ).

Somatic cilia 7–9 µm long in silver nitrate preparations ( Fig. 15 ). Invariably nine somatic and three preoral kineties with a total of 85 basal bodies on average ( Table 1). Kineties 3, 4 and 6 bipolar; kineties 1, 2, 5 and 7–9 shortened anteriorly and/or posteriorly. Kineties 1–4 on right side; kineties 5–7 on the left side; kineties 8 and 9 extend ventrally ( Table 1; Figs 4–6 , 9–11, 13–15 ).

Kinety 1 along upper right margin of oral cavity, forms an inverted sickle-shaped figure, consists of six narrowly spaced, usually ciliated dikinetids ( Figs 4 , 9, 11 ). Kinety 2 begins in second quarter of body with a single dikinetid and a single monokinetid, both ciliated and spaced very narrowly, resembling the characteristic trikinetid of D. sphagni ; followed by a very wide break, a single ciliated monokinetid, and one or two ciliated dikinetids near posterior end of body ( Figs 4, 5 , 14 ). Kinety 3 commences with a single, ciliated dikinetid followed by: (i) one or two widely spaced, ciliated monokinetids, (ii) a very wide break interrupt- ed in mid-body by a single, non-ciliated monokinetid, and (iii) a few, narrowly spaced, ciliated monokinetids and dikinetids near posterior end of body ( Figs 4, 5 , 14 ). Kineties 4 and 5 limit dorsal margin of body, all kinetids ciliated: kinety 4 commences with three widely spaced dikinetids followed by one or two widely spaced monokinetids, a very wide space in mid-body, and three widely spaced monokinetids posteriorly ( Figs 1, 5 , 9, 14 ); kinety 5 commences with a single dikinetid followed by five widely spaced monokinetids, ends near posterior quarter of cell ( Figs 2, 6 , 10, 15 ). Kinety 6 composed of widely spaced monokinetids forming indistinct pairs, usually only two and one kinetid ciliated in anterior and posterior end of row, respectively ( Figs 2, 6 , 10, 15 ). Kinety 7 begins in second quarter of body, consists of two widely spaced, non-ciliated monokinetids ( Figs 2, 6 , 10, 15 ). Kinety 8 consists of two segments ( Figs 4, 5 , 9, 11 ): anterior segment posterior to and very similar to preoral kinety 3, composed of two ciliated dikinetids and one ciliated monokinetid at left (posterior) end; posterior segment composed of three narrowly spaced monokinetids and a single monokinetid far posteriorly (see postoral complex below). Kinety 9 composed of three segments ( Figs 4, 5 , 9, 11 ): anterior segment left of adoral membranelles, composed of few, likely barren dikinetids recognizable only in appropriately oriented specimens; middle segment composed of one (rarely two) ciliated monokinetid far posterior to buccal cavity (see postoral complex); posterior segment composed of two ciliated monokinetids near rear cell margin. Postoral complex composed of the monokinetidal posterior segment of kinety 8 and the single, ciliated monokinetid in mid of kinety 9 ( Figs 1, 4, 5 , 9, 11, 14, 15 ).

Three preoral kineties each composed of ciliated dikinetids and a ciliated monokinetid at left end of kineties 2 and 3; occupy preoral ventral side and extend obliquely to left side ( Table 1; Figs 1, 4, 5 , 9, 11, 14, 15 ).

Oral apparatus slightly posterior to mid-body ( Table 1; Figs 1, 4, 5 , 9–11 ). Buccal cavity deep, contains membranelles 2 and 3 slightly obliquely arranged to main body axis and so close together that details cannot be recognized. Nasse kinetosomes and oral basket not recognizable.

Occurrence: This is a rather common species occurring, e.g., in Austria and Venezuela. Before its discovery in 1997, we did not separate it from D. revoluta .

Comparison of Drepanomonas minuta with similar species: Drepanomonas minuta belongs to a group of small species that have an acute (vs. rounded) anterior body end, viz., Drepanomonas revoluta and D. pauciciliata . Both are contained in the same preparation as D. minuta and thus can be easily compared. Drepanomonas revoluta Penard, 1922 , as redescribed by Foissner (1987) and Foissner et al. (1994), is slightly larger ( Table 1), has a deep, broad furrow (vs. flat) on the left side, has several (vs. 1–2) extrusomes, and differs in details of the somatic ciliature ( Table 1; Figs 7, 8 ). Drepanomonas pauciciliata Foissner, 1987 is slightly larger (22 vs. 20 µm in protargol preparations), has a slightly to distinctly convex (vs. flat) ventral side, a rather broad and deep furrow (vs. flat) on the left side, and several (vs. 1–2) extrusomes. In sum, D. minuta has a clear identity, i.e., a very small size, a flat left and right side, and only 1 or 2 extrusomes.

Figures

Figs 1–8. Drepanomonas minuta (1–6) and Drepanomonas revoluta (7, 8) from life (1–3, 7, 8) and after protargol impregnation (4–6).1, 2 – right and left side view of a representative specimen, length 20 µm, showing the flat cortex and the crenellations along the somatic kineties. This species has only 1 or 2 extrusomes and several non-ciliated basal bodies (arrowheads) in kineties 6 and 7; 3 – dorsal view showing the slightly convex right and left side; 4 – ventral view of a paratype specimen, showing the ventral ciliary pattern and the postoral complex. The anterior portion of kinety 2 is blended by the deeply impregnated macronucleus; 5, 6 – right and left side view of holotype specimen, length 20 µm. The kinetids of kinety 6 form widely spaced pairs; 7, 8 – Drepanomonas revoluta, right and left side view (from Foissner 1987). Note the deep furrow on the left side and the widely spaced kinetids of the postoral complex. E – extrusomes, K1–9 – somatic kineties, M – adoral membranelles, MA – macronucleus, MI – micronucleus, PC – postoral complex, PO(1–3) – preoral kineties, R – cortical ridges. Scale bars: 10 µm.

Figs 9–15. Drepanomonas minuta after protargol (9–13) and Klein-Foissner silver nitrate impregnation (14, 15). 9, 10 – right and left side view of the holotype and a paratype specimen, showing the kinetid pattern and the nuclear apparatus; 11 – ventral view of a paratype specimen, showing the obliquely arranged preoral kineties and the postoral complex; 12, 13 – right and left side view of paratype specimens, showing the slenderly semi-ellipsoidal body and the characteristic posterior extrusome;14, 15 – right and left side view, showing the kinetid pattern and the cytopyge. CY – cytopyge, E – extrusomes, K1–9 – somatic kineties, M – adoral membranelles, MA – macronucleus, MI – micronucleus, PC – postoral complex, PO(1–3) – preoral kineties. Scale bars: 10 µm.