Zoothamnium hiketes Precht, 1935

Sun, Ping, Song, Weibo, Ji, Daode & Hu, Xiaozhong, 2005, Redescription of Pseudovorticella cylindrica (Dons, 1915) nov. comb. and Zoothamnium hiketes Precht, 1935, two poorly defined marine peritrichs (Ciliophora: Peritrichia) from the north China Sea, Journal of Natural History 39 (32), pp. 2953-2965 : 2961-2964

Zoothamnium hiketes Precht, 1935

( Figures 19–38 ; Table I) Zoothamnium hiketes was originally described by Precht (1935) from the North Sea, Germany. No further studies have been carried out since then and hence neither the infraciliature nor silverline system is clear. Based on the Qingdao population and previous studies, an updated diagnosis and a detailed redescription are presented here.

New diagnosis

Marine Zoothamnium with dichotomously branched stalk. Zooids elongate, measuring about 40–80× 30–40 mm, with fine pellicular striations. Peristomial lip double-layered. Single contractile vacuole apically located. Macronucleus generally C-shaped and transversely orientated. Number of transverse lines from oral area to aboral ciliary wreath 89–109, from aboral ciliary wreath to scopula, 35–43.

Description of Qingdao population Zooids usually elongated vase-shaped, in vivo about 60–80× 30–40 mm, and only slightly constricted below the thick peristomial lip, which is inconspicuously double-layered; large peristomial disc highly elevated ( Figures 19 , 29 ).

Pellicle smooth when observed at low magnification, fine striations recognizable under high magnification (×400 or higher) ( Figure 31 ).

Cytoplasm colourless or slightly greyish, usually contains several to many large granules (4–8 mm in diameter) ( Figures 19 , 29 ). One large contractile vacuole apically located, contracting every 4 min ( Figure 19 ; Figure 30 , arrows). Macronucleus band-like, generally C-shaped, transversely orientated ( Figures 19, 20 ); micronucleus not observed.

Colony dichotomously branched with zooids located regularly in pairs ( Figures 23 , 27 ), consisting of up to 100 zooids in a large colony ( Figure 34 ). Stalk up to 400 mm long, diameter about 12 mm in main stalk and 6–8 mm in accessory branches. Surface of stalk smooth and often covered with rod-shaped bacteria (about 1.2–1.8 mm in length) ( Figures 21 , 28 , arrowheads). Spasmoneme about 2 mm in diameter, without visible mitochondria (thecoplasmic granules).

Oral infraciliature as shown in Figures 24, 25 , 33, 36, 38 , haplo- and polykinety circling about 1.5 turns around peristomial disc, and making a further turn after entering vestibulum. Near distal end of haplo- and polykinety, always one short kinety fragment recognizable ( Figure 25 , double arrowhead; Figure 36 , arrow).

At lower half of vestibulum, polykinety transforming into three peniculi (P1–3), each of which consists of three rows. P1 longer than other two, extending to cytostome. P2 interposes between P1 and P3 and ends at curvature of P1. Rows in P3 are parallel to each other ( Figure 33 ). Germinal kinety parallel to haplokinety within upper half of vestibulum ( Figure 25 ; Figure 38 , double arrowhead). Epistomial membrane located at opening of oral cavity ( Figures 25 , 38 , arrow). Aboral ciliary wreath formed by probably double-rowed kineties ( Figure 26 ; Figures 32, 35 , arrow; Figure 37 , arrowheads).

Silverline system genus typical, 89–109 striations between peristomial area and aboral ciliary wreath, 35–43 striations from aboral ciliary wreath to scopula, with many sparsely distributed pellicular pores ( Figures 26 , 35 ).

Comparison

Zoothamnium hiketes Precht, 1935 was originally found on the seta of Gammarus species as epizoons, and the brief description concerned only the morphology of live cells ( Precht 1935; Figure 22a, b ). Since then, no redescriptions have been made. In the absence of data concerning the infraciliature and silverline system, we identified our organism mainly on the basis of its body shape, appearance of the thick peristomial lip (inconspicuous doublelayered), position of contractile vacuole, branching form, and marine habitat. The only difference is the size of the zooid. According to the original description, the zooid of Z. hiketes is smaller, about 40–55 mm in length, while in the Qingdao population the length is about 60–80 mm. Since the size of the organism, to the authors’ knowledge, is usually a population-dependent feature in most cases, we consider this difference as an intra-species variation.

Morphologically, Zoothamnium cienkowskii Wrzesniowski, 1877 ( Figure 45 ; Table III) is similar to Z. hiketes in vivo. Unfortunately, neither the infraciliature nor silverline system of the former has been described. However, Z. cienkowskii can be distinguished at least by the appearance of the stalk (transversely wrinkled at accessory branch versus smooth) and differentiation of the zooids (having enlarged zooids versus all zooids about equal size) ( Kahl 1935).

Zoothamnium affine sensu Song, 1991 ( Figures 46, 47 ) whose infraciliature also remains unknown, matches in some aspects Z. hiketes , e.g. in body size, in branching form and in some other morphometric features (Table III). However, the former can be identified by having fewer silverlines between oral area and aboral ciliary wreath (75–81 versus 89–109) and a cross-striated stalk (versus smooth) ( Song 1991b).

Another similar form, Zoothamnium maximum Song, 1986 ( Figures 48, 49 ; Table III) differs from Z. hiketes in: (1) the larger size (80–120 versus 40–80 mm); (2) more silverlines between aboral ciliary wreath and scopula (45–58 versus 35–43); (3) the appearance of P3 (the outer row loosely ciliated, about two-thirds of the other two in length versus inner row slightly longer than the other two) ( Song 1986; Ji and Song 2004).

Zoothamnium duplicatum Kahl, 1933 ( Figures 50, 51 ; Table III) also exhibits a similar size and dichotomous branching pattern, but differs from Z. hiketes by the following features: (1) significantly fewer silverlines between peristomial area and aboral ciliary wreath (48–53 versus 89–109); (2) the form of P3 (outer two rows close set, with their upper halves separated widely from the inner one versus three rows parallel to each other) ( Ji et al., 2005).

Zoothamnopsis mengi Song, 1997 ( Figures 52, 53 ) and Zoothamnopsis sinica Ji and Song, 2004 ( Figures 54, 55 ) might also be similar to the present form (Table III). However, they differ from Z. hiketes by the different silverline system ( Pseudovorticella - type versus Vorticella - type) and the structure of P3 ( Song 1997; Ji and Song 2004).

Figures

Figures 19–26. Morphology of Zoothamnium hiketes from life (19–23), after protargol (24, 25) and silver nitrate impregnation (26). (19) General view of a typical zooid. (20) Showing varieties of body shape and macronucleus. (21) Detail of stalk, arrowheads show many rod-shaped bacteria on stalk surface. (22) Zoothamnium hiketes (from Precht 1935). (23) Colony form. (24) Detail of the three oral peniculi, arrows mark separated upper end of the outer two rows in P2. (25) Oral infraciliature, arrow notes epistomial membrane, double arrowhead indicates the oral distal fragment. (26) Silverline system. ACW, aboral ciliary wreath; G, germinal kinety; H, haplokinety; P1–3, peniculi 1–3; Po, polykinety. Bars: 30 mm (19); 20 mm (21, 22a); 100 mm (22b); 150 mm (23).

Figures 27–38. Photomicrographs of Zoothamnium hiketes from life (27–31), after protargol (32–34, 36–38) and silver nitrate impregnation (35). (27) Colony at low magnification. (28) Detail of stalk, arrowheads showing rodshaped bacteria on stalk surface. (29) Zooids at 400× magnification. (30) Varieties of body shape, arrows indicate contractile vacuole. (31) Lateral view of a zooid at 1250× magnification, showing the pellicle striations. (32) Arrows mark aboral ciliary wreath. (33) Oral apparatus, indicating three peniculi (P1–3). (34) To show the branching form. (35) General silverline system, arrow marks the aboral ciliary wreath. (36) Arrow showing the distal fragment of oral apparatus. (37) General appearance, to mark aboral ciliary wreath (arrowheads). (38) To show epistomial membrane (arrow) and germinal kinety (double arrowhead). P1–3, peniculi 1–3. Scale bars: 200 mm (27); 50 mm (29); 70 mm (30); 100 mm (34).

Figures 45–55. Comparison of some morphotypes closely related to Zoothamnium hiketes. (45) Zoothamnium cienkowskii (from Kahl 1935). (46, 47) Zoothamnium affine (from Song 1991b). (48, 49) Zoothamnium maximum (from Ji and Song 2004). (50, 51) Zoothamnium duplicatum (from Ji et al. 2005). (52, 53) Zoothamnopsis mengi (from Song 1997). (54, 55) Zoothamnopsis sinica (from Ji and Song 2004). Scale bars: 50 mm (45, 46, 48, 50, 52, 54); 100 mm (47, 51, 53); 300 mm (49, 55).