Zoothamnium plumula Kahl, 1933

Ji, Daode, Shin, Mann Kyoon, Choi, Joong Ki, Clamp, John C., Al-Rasheid, Khaled A. S. & Song, Weibo, 2011, Redescriptions of five species of marine peritrichs, Zoothamnium plumula, Zoothamnium nii, Zoothamnium wang, Pseudovorticella bidulphiae, and Pseudovorticella marina (Protista, Ciliophora), Zootaxa 2930, pp. 47-59 : 48-51

Zoothamnium plumula Kahl, 1933

( Fig. 1 ; Table 1)

Emended diagnosis. Marine Zoothamnium with colony up to 3 mm high; elongate, median primary stalk giving rise to secondary stalks in regular alternate series in single plane to create feather-shaped outline. Zooids conical to vase-shaped, measuring 50–75 × 35–45 µm in vivo; peristomial lip thick, without medial, circumferential infolding when expanded. Macronucleus C-shaped, transversely oriented, located in oral half of cell. Pellicular striations closely spaced and indistinct at lower magnifications; 50–70 silverlines lying between peristomial lip and trochal band and 20–30 between trochal band and scopula. P3 consists of three rows of kinetosomes that are equal in length; row 1 separated from rows 2 and 3 by gap in abstomal quarter and all three rows converging adstomally.

Redescription. Colony large, up to 3 mm tall and including over 500 zooids. Secondary stalks up to 800µm long, branching off elongate primary stalk in regular, alternate series in one plane; tertiary stalks with same pattern of branching, measuring less than 120µm in length ( Figs. 1 B, D–F, J). Secondary stalks increasing slightly in length from most basal ones to medial region of colony and then decreasing in length toward tip of colony to create feather-shaped outline. Occasionally, most basal secondary stalk more highly developed and considerably longer than other secondary stalks ( Fig. 1 D). Stalk with diameter of 16 µm in basal portion of primary stalk, narrowing progressively to diameter of 8 µm at distal ends of tertiary stalks; cortex of stalk colorless and transparent, with smooth surface and fine longitudinal striations in interior. Spasmoneme relatively more dense than cortex of stalk, with diameter of 5–6 µm in primary stalk, narrowing progressively to diameter of 2.5 µm at distal ends of tertiary stalks; band of mitochondria, visible as dark granules with diameter of 0.8 µm, winding along helical path just beneath surface of spasmoneme ( Fig. 1 L). Colony relatively insensitive to stimulation, requiring strong turbulence or excitation to initiate full contraction of entire colony, usually contracting only partially when touched with needle.

Zooids elongate, subconical, usually 50–75 µm (n=11) long; body widest at peristomial lip, which measures 35–45 µm (n=11) in diameter ( Figs. 1 A, K). Small number of enlarged zooids (macrozooid?) measuring up to 90– 100 × 50–60 µm usually present on middle or distal parts of secondary stalks ( Figs. 1 B, F, J). Body slightly constricted below peristomial lip, which lacks a secondary, circumferential infolding (compare with Fig. 2 A); epistomial disc moderately elevated above peristomial lip ( Fig. 1 A). Pellicular striations easily visible above × 400 magnification ( Fig. 1 M), but surface of body appears uniformly smooth at low magnifications. Telotroch discoid, measuring 25–30µm x 50 –60 µm.

Cytoplasm of zooids packed with tiny (0.8–1.5 µm diameter), dense granules visible only at high magnification (×1000); cell colorless or slightly grayish at low magnifications. Food vacuoles and items of food within them variable in size, randomly distributed in body. Single contractile vacuole in adoral position beneath epistomial disc and near dorsal wall of infundibulum. Macronucleus C-shaped, transversely oriented, surrounding micronucleus and lower half of infundibulum ( Fig. 1 A).

Oral infraciliature as shown in Figures 1 H, I, N-P. Haplo- and polykinety making one and one-quarter circuits around peristome and one additional circuit within infundibulum. Haplokinety and polykinety parallel on peristome, diverging within infundibulum to lie on opposite walls ( Fig. 1 H). Epistomial membrane short, located at entrance into infundibulum (arrows in Figs. 1 H, P). Germinal kinety running parallel to haplokinety in adoral half of infundibulum ( Figs. 1 H, O, arrow). Each of three infundibular polykineties (P1–P3) consisting of three rows of kinetosomes. All rows of Pl terminating adstomally at level of cytostome; rows of P2 terminating adstomally at adstomal curvature of P1. Rows of P2 terminating abstomally without merging with P1; abstomal 1/4 of row 3 of P2 diverging from other rows of P2 ( Figs. 1 H, I, N). All rows of P3 terminating adstomally at point slightly beyond adstomal end of P2 and abstomally at point approximately 1/3 of distance from adstomal to abstomal end of P2. Rows 2 and 3 of P3 closely parallel to row 1 in adstomal half, diverging from it in abstomal half, converging again with it at abstomal end of P3 ( Fig. 1 I).

Trochal band consisting of band of dikinetids encircling cell at point 3/4 of distance from peristome to scopula.

Silverline system consisting of closely spaced, parallel, transverse silverlines ( Figs. 1 G, Q); 50–60 silverlines present between peristome and trochal band, 22–27 between trochal band and scopula. Pellicular pores sparsely distributed alongside silverlines ( Fig. 1 Q)

Remarks. The Chinese population of Z. plumula that we examined is characterized mainly by the following characters: alternately branched stalk, feather-shaped outline of colony, presence of larger zooids at some points on secondary stalks, and marine habitat. Characteristics of the colonies that we observed matched well with both the original description by Kahl (1933, 1935; Figs. 1 B, C) and the redescription by Song et al. (2002; Figs. 1 A, G). Consequently, the identification of our samples as Z. plumula is beyond reasonable doubt.

In the experience of the senior author, Z. plumula is usually abundant in eutrophic waters and is accompanied by Z. alrasheidi Ji et al., 2009 , which forms a large, leaf-shaped colony with a similar branching pattern. However, the latter species can be distinguished from Z. plumula easily by differences in infraciliature and number of silver lines, its larger zooids (80–120 × 50–60 µm vs. 50–75 × 35–45 µm), and its thick peristomial lip, which has a prominent circumferential infolding (Ji et al. 2009).

At first glance, two other marine congeners, Z. alternans Claparède and Lachmann, 1859 and Z. niveum Ehrenberg, 1838 , are very similar to Z. plumula in shape of the colony, branching pattern, and presence of macrozooids. However, zooids of both Z. alternans and Z. niveum have different sizes than those of Z. plumula (40–56 × 26–32 µm and 54–66 × 16–22 µm vs. 50–75 × 35–45 µm), and the macrozooids of both species are located on the primary stalk rather than in on the middle or distal parts of secondary branches, as in Z. plumula . In addition, Z. niveum forms a considerably larger colony (> 1 cm vs. 3 mm in Z. plumula ) ( Bauer-Nebelsick et al. 1996; Ji et al. 2006 b).

Characters Min Max Mean SD n

Number of silverlines from Z. plumula 50 60 54.5 3.36 11 peristomial lip to trochal Z. nii 47 58 52.1 3.38 15 band Z. wangi 70 85 76.4 4.63 8 P. bidulphiae 25 31 28 2.26 10 P. m a r i n a 25 30 27.5 - 4 Number of silverlines from Z. plumula 22 27 25.3 1.57 10 scopula to trochal band Z. nii 22 30 27.4 3.04 11 Z. wangi 38 50 44.2 4.46 12 P. bidulphiae 9 13 11.6 1.30 8 P. m a r i n a 10 15 12 1.79 6

Figures

FIGURE 1. Morphology of Zoothamnium plumula from live cells (A – F, J – M), after staining with protargol (H, I, N – P), and after staining with silver nitrate (G, Q) (A, G from Song et al. 2002; B, C after Kahl 1933). A. General view of a typical zooid. B, D – F. Different colony forms. C. Comparison of normal zooid with enlarged zooid. G. Silverline system, arrow marks the trochal band. H. Oral infraciliature, arrow marks the epistomial membrane, double-arrow indicates the distal fragment. I. Detail of infundibular polykineties. J. Branching pattern of a typical colony. K. Variations in shape of zooids. L. Detail of stalk, arrows mark mitochondria. M. Pellicular striations. N. Arrangement of infundibular polykineties. O. Germinal kinety (arrow) and radial myonemes in cell body (arrowheads). P. Epistomial membrane (arrow). Q. General view of silverline system. Abbreviations: G, germinal kinety; H, haplokinety; P 1 - 3, infundibular polykinety 1 – 3; Po, polykinety. Scale bars: 30 Μm (Fig. A), 100 Μm (Fig. K), 400 Μm (Figs. F, J).

FIGURE 2. Morphology of Zoothamnium nii and its synonyms from live cells (A, C – G, I – L, O, P, R), after staining with protargol (B, H, M, N), and after staining with silver nitrate (Q). A. General view of a typical zooid. B. Detail of infundibular polykineties. C, D. Zoothamnium duplicatum, after Kahl (1933). E, J. form of colony. F, G. Zoothamnium sp. after Kahl (1935). H. Oral view of the oral apparatus, arrow marks the epistomial membrane. I, K, L. Variations in shape of zooids. M. Lateral view showing macronucleus (dark area) and micronucleus (arrow). N. Macronucleus (dark area) and germinal kinety (arrow). O, P. Zooids at high magnification showing pellicuilar striations and variations in shape of the body. Q. General view of silverline system. R. Telotroch. Abbreviations: G, germinal kinety; H, haplokinety; P 1 – 3, infundibular polykinety 1 – 3; Po, polykinety. Scale bars: 40 Μm (Figs. A, O, R), 50 Μm (Figs. L, P), 300 Μm (Figs. D – F, J, K).