Metaradiophrya lumbrici ( Dujardin, 1841 )

Obert, Tomáš & Vďačný, Peter, 2019, Integrative taxonomy of five astome ciliates (Ciliophora, Astomatia) isolated from earthworms in Central Europe, European Journal of Taxonomy 559, pp. 1-37 : 7-12

Metaradiophrya lumbrici ( Dujardin, 1841)

Figs 2 , 3 , 4 , 5

Description

The body size is about 105–230 × 55–130 µm, with an average of 170 × 100 µm. The shape is ovate to elliptical with an anterior body end rounded and posterior end broadly rounded to truncate. The cell is distinctly dorsoventrally flattened ( Figs 2A, F , 3B , F–M, 4A–B, E–F). On the ventral side, about 10 µm away from the anterior body end, there is a conspicuous fibrillar hook composed of two unequally long arms. The longer arm is 25–35 µm long, flat and completely situated underneath the cell surface. The shorter arm is 8–13 µm long, usually appears slightly more robust at the base and projects from the cell in lateral view. A set of very distinct fibers is associated with the hook: on average 6 (5–7) fibers are attached to the upper right side of the longer arm, on average 33 (30–37) fibers to the ventral side of the longer arm and on average 11 (8–13) fibers to the left side of the shorter arm ( Figs 2 A–C, 3A, 5).

The nuclear apparatus is composed of a macronucleus and a micronucleus. The macronucleus is rodlike with both ends rounded. It begins about 27 µm away from the anterior body margin and ends about 12 µm above the posterior body margin. Its length spans a range from approximately 85 to 200 µm and its width ranges from 8 to 18 µm, averaging at 13 µm. The macronuclear surface is smooth and without any irregularities, however, small vesicules appear in its vicinity in dying cells. The micronucleus is typically situated close to the mid-portion of the macronucleus. The shape of micronucleus is circular to elliptical and its diameter is approximately 7 µm. The central region of micronucleus appears homogenous and brighter than its margin in the differential interference optics and might represent a central nucleolus ( Figs 2 F–G, 3B–M, 4A, C–D).

There are invariably two staggered rows of contractile vacuoles, extending right and left of the macronucleus. Their number ranges from 3 to 12 with an average of 6 vacuoles in the right row and from 3 to 11 with an average of 6 vacuoles in the left row ( Figs 2A , F–G, 3B, F–M, 4B–D). The cytoplasm is colorless and contains innumerable granules being ca 0.4 µm across and rod-like bacteria being about 3–15 µm long ( Figs 2G , 4 C–D). The cortex is rigid and without any specific granules ( Fig. 5 ). Swims moderately fast by rotation about the main body axis.

Somatic ciliature is holotrichous and composed of very densely ciliated and narrowly spaced kineties. The ventral ciliature is interrupted by a subapical suture that extends from the right body margin over the fibrillar hook towards the left body margin. Somatic kineties above the suture run towards the anterior body end where they curve onto the dorsal body side to meridionally extend over its surface towards the posterior body end. Somatic kineties below the suture run meridionally over the ventral side towards the posterior body end ( Figs 2 A–B, 3A, 4E–F, 5). The number of kineties on each body side ranges from 60 to 78. Lateral kineties form a right and a left subterminal suture in the posterior body region ( Figs 2 D–E, 4E).

Occurrence

Metaradiophrya lumbrici was detected exclusively in a group of anecic earthworms, namely, in L. terrestris at three localities: in gardens in the Šúrska ulica street in Rendez and in the Jakubská ulica street in Rača as well as in floodplain soils in a riparian, willow-poplar forest near the Karlova Ves branch of the Danube River ( Table 2 ). Ciliates were typically isolated from the middle part of the gastrointestinal tract, although very rarely one or two specimens were recorded also slightly above and below this gut region.

Figures

Fig. 2. Metaradiophrya lumbrici (Dujardin, 1841), Slovak specimens in vivo. A. Semi-schematic diagram of the ventral side, showing the fibrillar hook as well as the contractile vacuole and the somatic ciliary pattern. Arrowheads mark the subapical suture extending from the right body margin over the hook towards the left body margin. B. Detail of the anterior body portion, showing the fibrillar hook and its associated fibers. There are on average 6 (5–7) fibers attached to the upper right side of the longer arm, on average 33 (30–37) fibers to the ventral side of the longer arm and on average 11 (8–13) fibers to the left side of the shorter arm. C. Shape variants of fibrillar hooks. The hook is composed of two unequally long arms: the longer arm is flat and 25–35 µm long, while the shorter arm appears slightly more robust at the base and is 8–13 µm long. D–E. Lateral somatic kineties form a right and a left subterminal suture in the posterior body region. F. Ventral view, showing the general body organization. G. The cytoplasm contains innumerable granules being ca 0.4 µm across and rod-like bacteria being about 3–15 µm long. Scale bars: A, F = 50 µm; B = 10 µm.

Fig. 3. Metaradiophrya lumbrici (Dujardin, 1841), Slovak specimens in vivo. A. Detail of the anterior body portion, showing the fibrillar hook and its associated fibers. There are on average 6 (5–7) fibers attached to the upper right side of the longer arm, on average 33 (30–37) fibers to the ventral side of the longer arm and on average 11 (8–13) fibers to the left side of the shorter arm. Arrowheads mark the subapical suture extending from the right body margin over the fibrillar hook towards the left body margin. B, F–M. Variability of body shape and size as well as of the contractile vacuole and nuclear apparatus. Drawn to scale. C–E. The macronucleus is rod-like and its surface is smooth or with some indistinct irregularities. However, many small vesicules appear in its vicinity in dying cells. The micronucleus is elliptical and typically situated close to the mid-portion of the macronucleus. Scale bars: A = 20 µm; B, F–M = 100 µm.

Fig. 4. Metaradiophrya lumbrici (Dujardin, 1841), Slovak specimens in vivo. A–B. Ventral view of representative specimens, showing the typical body shape, localization of the fibrillar hook, the long rod-like macronucleus and two staggered rows of contractile vacuoles (arrowheads). C–D. Detail, showing the long rod-like macronucleus, a single micronucleus, contractile vacuoles and cytoplasmic bacteria. The central region of the micronucleus appears homogenous and brighter than its margin in the differential interference optics and might represent a central nucleolus. E–F. Somatic ciliature is holotrichous and composed of very densely ciliated meridional kineties. In the posterior body region, lateral somatic kineties form a right and a left subterminal suture (arrow in E), whose detail is shown in the left inset. Scale bars: A–B = 100 µm; C–D = 10 µm; E–F = 20 µm.

Fig. 5. A–B. Metaradiophrya lumbrici (Dujardin, 1841), Slovak specimens in vivo. Details of the anterior body portion, showing the fibrillar hook and its associated fibers. There are on average 6 (5–7) fibers attached to the upper right side of the longer arm, on average 33 (30–37) fibers to the ventral side of the longer arm and on average 11 (8–13) fibers to the left side of the shorter arm. Arrowheads mark the subapical suture extending from the right body margin over the fibrillar hook towards the left body margin. The somatic kineties above the suture run towards the anterior body end where they curve onto the dorsal body side to meridionally extend over its surface towards the posterior body end. On the other hand, the somatic kineties below the suture run meridionally over the ventral side towards the posterior body end. The ventral somatic kineties are lined with fibers attached to the fibrillar hook. Scale bars: 20 µm.