VORTICELLIDAE Ehrenberg, 1938

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 : 2954-2959

Family VORTICELLIDAE Ehrenberg, 1938

Genus Pseudovorticella Foissner and Schiffmann, 1974 Pseudovorticella cylindrica ( Dons, 1915) nov. comb.

( Figures 1–18 ; Table I) Synonym Vorticella cylindrica Dons, 1915 . Since no ciliature information was previously available for this organism, here we supply an improved diagnosis and detailed data on the infraciliature as well as on the morphology of living cells, based on the Qingdao population.

Revised diagnosis Inverted bell-shaped Pseudovorticella , length in vivo 40–50 mm and length: width ratio about

1:1; macronucleus J-formed; one contractile vacuole apically located; reticulate silverline system with 33–40 transverse striations between oral area and aboral ciliary wreath, and

14–19 striations between aboral ciliary wreath and scopula. The inner row of peniculus 3 conspicuously shorter than other two. Marine.

Description

Cell constant in size and shape, about 40–50× 45–50 mm in vivo, usually with a slight constriction in the aboral region. Maximum width of cell at peristomial area with thin and relatively rigid peristomial lip (PL; Figures 1, 5 , 9 ). Peristomial disc (PD) flat and only slightly elevated when cell fully extended ( Figures 1 , 9 ). Pellicle generally smooth, while a finely reticulate pattern of striations can be observed only under high magnification (1000×) ( Figure 1 ).

Cytoplasm colourless or greyish, usually containing several refractive particles, 4–7 mm in length ( Figures 1, 5 , 13 ). Single contractile vacuole large, apically located, contracting every 2–3 min. Macronucleus J-formed, variable in shape and generally situated transversely ( Figure 7 ). Micronucleus not observed.

Stalk usually two to four times zooid length, relatively thick and about 5 mm in diameter ( Figure 11 ). The spasmoneme (Spa) about 2 mm in diameter, with a string of conspicuous, dark grey thecoplasmic granules (ca 0.3 mm in diameter) ( Figures 2 , 10 , arrows).

Individuals often closely grouped together thus forming pseudocolonies of up to 30 zooids. Telotroch (swarmer) was not observed.

Infraciliature as shown in Figures 6 , 12, 15, 17, 18 . Haplokinety (H) and polykinety (Po) describing about 1.5 turns around peristomial disc before entering vestibulum, where they make a further turn. Similar to that of other congeners, polykinety forms three peniculi in lower half of vestibulum, each consisting of three rows. The posterior ends of peniculus 1 (P1) and P3 terminate at the same level whereas P2 situates between and terminates conspicuously above P1 and P3 ( Figures 6 , 15 ). The inner row of P3 is characteristically displaced relative to the other two: very short, about one-third length of the outer two rows which converge with P1. The haplokinety passing around the vestibulum on the opposite wall to the peniculi. Germinal kinety (G) consisting of zig-zag structure of kinetosomes and extending to the upper one-third of the vestibulum, where it passes immediately beyond the haplokinety ( Figure 6 ). The epistomial membrane is short, located near the opening of the infundibulum ( Figures 6 , 12 , arrow). Aboral ciliary wreath encircles cell in posterior region and seems to be composed of a Z-rowed structure ( Figure 14 , double arrowhead; Figure 17 , arrowheads).

Silverline system reticulate ( Figure 16 ). Transverse lines in the anterior region of the cell are more widely spaced than those in the posterior region ( Figures 8 , 14, 16 ). The number of transverse silverlines from peristome to aboral ciliary wreath (5aboral trochal band), 33– 40; from aboral ciliary wreath to scopula, 14–19 ( Table I).

Comparison

Pseudovorticella cylindrica was originally described by Dons (1915) ( Figure 3 ) under the name of Vorticella cylindrica . Its infraciliature remained unknown though it was redescribed in the last decade by Song (1991a) ( Figure 4 ). The Qingdao population resembles the previous descriptions in all aspects, e.g. body shape, size, number of contractile vacuoles, as well as marine habitat, hence we are confident that the identification is correct.

A summary of comparisons between P. cylindrica and similar Pseudovorticella and Vorticella spp. is given in Table II.

Morphologically, Pseudovorticella patellina (Müller, 1776) Song and Warren, 2000 ( Figure 39 ) should be closely related to P. cylindrica . Nevertheless, the former differs from P. cylindrica in its larger size (55–110 versus 40–50 mm), the number of transverse silverlines between the aboral ciliary wreath and the anterior end (19–22 versus 33–40), number of contractile vacuoles (two versus one), and the extreme outwards extension of the peristomial lip. In addition, the structure of peniculus 3 is completely different (see Song and Warren 2000).

Pseudovorticella punctata (Dons, 1918) Warren, 1987 ( Figure 43 ) is most similar to P. cylindrica , especially in terms of body size and the habitat. However, P. punctata can be clearly distinguished from the latter by the appearance of the peristomial lip (considerably thick versus thin), the lower position of the contractile vacuole (below the vestibulum versus apically located), and having significantly fewer transverse lines (about 30 versus 52) ( Warren 1987).

Considering the general morphology, further comparisons should be also made with some Vorticella species. Vorticella campanula Ehrenberg, 1831 ( Figures 40, 41 ) corresponds very well in vivo with Pseudovorticella cylindrica . In the past 80 years, P. cylindrica was repeatedly considered to be a marine variety of V. campanula ( Noland and Finley 1931; Warren 1987). In 1992, a thorough redescription of V. campanula using modern techniques was given by Foissner et al. (1992). Thus, we have the opportunity to compare these two forms. Vorticella campanula can be separated from P. cylindrica by size (50–160 versus 40–50 mm), the habitat (freshwater versus marine), Vorticella - type silverline system (versus Pseudovorticella pattern), and dissimilarities considering the infraciliature ( Foissner et al. 1992).

Vorticella nebulifera Müller, 1786 also bears some resemblance to Pseudovorticella cylindrica , particularly with respect to the smooth pellicle and cell size. However, the two taxa can be clearly separated by the position of the contractile vacuole (lower ventral versus apically dorsal located) ( Figure 42 ), different pattern of silverline system, and the body shape (slender in V. nebulifera ) ( Song 1991a).

With reference to body shape and the habitat, another similar form, Vorticella marina Greeff, 1870 whose silverline system and infraciliature remain unclear, should also be compared with P. cylindrica . The former differs from the latter, even at the in vivo level, in the lower position of contractile vacuole ( Figure 44 ) and appearance of pellicle (distinctly striated versus finely striated) ( Song 1991a).

Figures

Figures 1–8. Morphology of Pseudovorticella cylindrica from life (1–5), after protargol (6, 7) and silver nitrate impregnation (8). (1) A typical zooid. (2) Detail of stalk, arrows to show conspicuous thecoplasmic granules in spasmoneme. (3) From Dons (1915) (called Vorticella cylindrica). (4) From Song (1991a) (called Vorticella cylindrica). (5) Typical zooids at low magnification. (6) Buccal apparatus, arrow indicates epistomial membrane. (7) Variable shape of macronucleus. (8) Silverline system. ACW, aboral ciliary wreath; G, germinal kinety; H, haplokinety; P1–3, peniculi 1–3; PD, peristomial disc; PL, peristomial lip; Po, polykinety; Sc, scopula; Spa, spasmoneme. Scale bars: 30 mm (1); 20 mm (4); 50 mm (5).

Figures 9–18. Photomicrographs of Pseudovorticella cylindrica from life (9–11, 13), after protargol (12, 15, 17, 18) and silver nitrate impregnation (14, 16). (9) A fully extended zooid at low magnification. (10) Detail of stalk, arrows show thecoplasmic granules in spasmoneme. (11) Zooids at low magnification. (12) Arrow indicates epistomial membrane. (13) A contracted zooid at low magnification. (14, 16) Silverline system, showing reticulate meshes, double arrowhead marks aboral ciliary wreath. (15) Anterior end of zooid showing peniculi 1–3. (17) Lateral view, showing aboral ciliary wreath (arrowheads). (18) Apical view, showing polykinety and haplokinety. H, haplokinety; P1–3, peniculi 1–3; Po, polykinety. Scale bars: 120 mm (9); 200 mm (11); 60 mm (13).

Figures 39–44. Species of Vorticella and Pseudovorticella that are similar to Pseudovorticella cylindrica. (39) Pseudovorticella patellina (from Song and Warren 2000). (40) Vorticella campanula (from Kahl 1935). (41) Vorticella campanula (from Noland and Finley 1931). (42) Vorticella nebulifera (from Song 1991a). (43) Pseudovorticella punctata (from Warren 1987). (44) Vorticella marina (from Song 1991a). Scale bars: 70 mm (39); 30 mm (41, 42); 20 mm (43, 44).