Fig 1.
Photomicrographs of Metasterkiella koreana from life.
(A, B) Specimens, showing body shape. (C, D, G) Slightly compressed specimens due to cover slip pressure, showing cytoplasmic crystals and lipid droplets. (E) Section, showing the buccal wall and postoral ventral cirri. (F) A squeezed specimen, showing the lipid droplets and the cytoplasmic crystals mainly around the margin of the cell. (H) Nuclear apparatus in ventral view. (I–K) Resting cyst. Optical section (I), showing the cyst wall (opposed arrowheads). Surface view (J), showing the wrinkled hyaline ridges (opposed arrowheads). Squeezed cyst (K), showing cyst wall (opposed arrowheads). AZM, adoral zone of membranelles; BW, buccal wall; C, crystals; CV, contractile vacuole; FV, food vacuoles; L, lipid droplets; MA, macronuclear nodules; MI, micronuclei; S, scutum; IV/2, V/4, V/3, postoral ventral cirri. Scale bars = 15 μm (E, H–K) and 40 μm (A–D, F, G).
Fig 2.
Line diagrams of Metasterkiella koreana from life (A–E) and after protargol impregnation (F, G).
(A) A representative cell with a length of 85 μm. (B, C) Body shape of partially starved (B) and well fed (C) specimens. (D) Dorsolateral view. (E) Cytoplasmic crystals. (F, G) Ventral view of the holotype (F) and dorsal view of a paratype specimen (G), showing the ciliature and the nuclear apparatus. AZM, adoral zone of membranelles; CC, caudal cirri; DK1,4, dorsal kineties; DM1,2, dorsomarginal kineties; E, endoral membrane; LM, left marginal row; MA, macronuclear nodules; MI, micronuclei; P, paroral membrane; RM, right marginal row; I/1, II/3, III/3, frontal cirri; II/2, buccal cirrus; III/2, IV/3, VI/3, VI/4, fronto-ventral cirri; IV/2, V/4, V/3, postoral ventral cirri; V/2, VI/2, pretransverse ventral cirri; II/1, III/1, IV/1, V/1, VI/1, transverse cirri. Scale bars = 40 μm.
Fig 3.
Photomicrographs of Metasterkiella koreana after protargol impregnation.
(A) Ventral view of the holotype specimen. (B–F) Paratype specimens, showing body shape, nuclear apparatus, and ciliature of the ventral (B–D) and dorsal surface (E, F). Rarely a specimen (F) with three macronuclear nodules occurs. Arrowheads in (A–D) point to the pretransverse ventral cirri. AZM, adoral zone of membranelles; BC, buccal cirrus; CC, caudal cirri; DK1,3,4, dorsal kineties; DM1,2, dorsomarginal kineties; E, endoral membrane; FC (1, 3), frontal cirri; FVC, frontoventral cirri; LM, left marginal row; MA, macronuclear nodules; MI, micronuclei; P, paroral membrane; PC, postoral cirri; RM, right marginal row; TC, transverse cirri; V/3, postoral ventral cirrus. Scale bars = 40 μm.
Table 1.
Morphometric data on Metasterkiella koreana n. gen., n. sp.
Fig 4.
Line diagrams of protargol stained early dividers of Metasterkiella koreana.
(A) Oral primordium develops close to transverse cirri. (B) Two anlagen arise from anterior of the oral primordium. (C, D) Anlage II of the opisthe moves anteriorly incorporating the postoral cirrus IV/2, part of this anlage merges with the parental buccal cirrus in early divider. Arrowhead points to the de novo origin of the rightmost anlagen for the proter and the opisthe. (E, F) The anterior portion of the de novo originated anlage moves anteriorly; while the posterior portion elongates incorporating cirrus V/3 and splits longitudinally forming anlagen V and VI of the opisthe. Postoral cirrus V/4 disaggregates and contributes to form the growing anlage IV of the opisthe. A rare specimen (F), showing the late disaggregation of cirrus V/3 (double arrowheads), already dissolved in previous stages. Overall, six parental cirri (II/2, III/2, IV/2, IV/3, V/3, and V/4) disaggregate to give rise to five fronto-ventral—transverse anlagen for proter and opisthe. AM, adoral membranelles; AZM, adoral zone of membranelles; E, endoral membrane; FC3, frontal cirrus 3; FVC, frontoventral cirri; LM, left marginal row; MA, macronuclear nodules; OP, oral primordium; P, paroral membrane; PC, postoral cirri; RM, right marginal row; TC, transverse cirri; V/3, V/4, postoral ventral cirri. Numerals denote cirral anlagen. Scale bars = 40 μm.
Fig 5.
Line diagrams of protargol stained early (A–C, F), middle (D, G), and late dividers (E) of Metasterkiella koreana.
(A, B) The anterior portion of the de novo originated anlage splits longitudinally forming anlagen V and VI of the proter. Cirrus IV/3 begins to disagreegate forming proter’s anlage IV, cirrus III/2 form the anlage III. (C) Four anlagen for marginal cirri develop incorporating four to five parental marginal cirri in the proter and the opisthe. (D, E) The newly formed fronto-ventral-transverse cirri migrate to their specific sites and dorsomarginal kineties develop close to the newly formed right marginal row. (F, G) Specimens, showing the details of the morphogenetic event on the dorsal surface with respect to the nuclear division. Within row formation of the anlagen for dorsal kineties 1–3 (F). Dorsal kinety 3 undergoes simple fragmentation forming kineties 3 and 4 (G). Caudal cirri are formed at the posterior end of dorsal kineties 1, 2, and 4, and the newly formed dorsomarginal kineties shift to the dorsal surface. AM, adoral membranelles; AZM, adoral zone of membranelles; CC, caudal cirri; DK1–4, dorsal kineties; DM1,2, dorsomarginal kineties; FC3, frontal cirrus 3; LM, left marginal row; MA, macronuclear nodules; OP, oral primordium; P, paroral membrane; RM, right marginal row; TC, transverse cirri; Numbers denote cirral anlagen. Scale bars = 40 μm.
Fig 6.
Photomicrographs of Metasterkiella koreana after protargol impregnation.
For explanation refer to the legend of Fig 4A–4F. Double arrowheads and arrowheads in (C–E) point the anterior and the posterior portion of the rightmost anlagen for the proter and the opisthe which originates de novo. Arrowhead in (F) points to the disaggregating cirrus III/2 which forms anlage III of the proter. AZM, adoral zone of membranelles; E, endoral membrane; FC3, frontal cirrus 3; FVC, frontoventral cirri; LM, left marginal row; MA, macronuclear nodules; MI, micronuclei; OP, oral primordium; RM, right marginal row; TC, transverse cirri; V/3, V/4, postoral ventral cirri. Numerals denote cirral anlagen. Scale bars = 40 μm.
Fig 7.
Photomicrographs of Metasterkiella koreana after protargol impregnation.
For explanation refer to the legend of Fig 5A–5G. Arrowhead in (A) points to the anterior portion of the opisthe’s anlage II which moves anteriorly of the buccal vertex and merges with the parental buccal cirrus in early dividers. Arrowheads in (F) point to dorsal kinety 4 for the proter and the opisthe, which is formed by the simple fragmentation of dorsal kinety 3. AM, adoral membranelles; AZM, adoral zone of membranelles; CC, caudal cirri; DK1, dorsal kinety 1; DM1,2, dorsomarginal kineties; FC3, frontal cirrus 3; FV, food vacuole; LM, left marginal row; MA, macronuclear nodules; MI, micronuclei; OP, oral primordium; RM, right marginal row; TC, transverse cirri; Numerals denote cirral anlagen. Scale bars = 40 μm.
Fig 8.
Bayesian tree inferred from the SSU rRNA gene sequences, showing the phylogenetic position of Metasterkiella koreana (bold).
Codes following the names are GenBank accession numbers. Numbers at the nodes represent the Bayesian inference (BI) posterior probabilities and the maximum likelihood bootstrap values out of 1000 replicates. A hyphen (-) represents differences between the BI and ML tree topologies. The scale bar corresponds to two substitutions per 100 nucleotide positions.