Pseudepistylis songi, Peng, Xiaohui, Shi, Xinlu & Warren, Alan, 2007

Peng, Xiaohui, Shi, Xinlu & Warren, Alan, 2007, Establishment of a new peritrich ciliate genus, Pseudepistylis n. gen. (Ciliophora: Peritrichia: Epistylididae), with a description of a new freshwater species, Pseudepistylis songi n. sp. from Wenzhou, China, Zootaxa 1524, pp. 35-45 : 37-42

Pseudepistylis songi n. sp.

( Table 1 ; Figs. 1–37 )

Diagnosis: Limnetic species with transparent or translucent, dichotomously branched stalk. Zooids elongate, bell-shaped, measuring 220 × 140 μm in vivo on average, with thick peristomial lip that is invariably reflected aborally. One contractile vacuole located on dorsal wall of infundibulum. Macronucleus C-shaped and transversely oriented. More than 137 transverse silverlines between oral area and aboral ciliary wreath, on average 77 between aboral ciliary wreath and scopula. Haplokinety and polykinety make one and one-quarter turns on peristome; terminal ends of kineties of infundibular polykinety 2 terminate adstomally at different levels within infundibulum.

Type specimens: One holotype (registration number WZ2005102504) and one paratype slide (WZ2006110204) with protargol and silver nitrate impregnated specimens respectively are deposited in the Laboratory of Zoological Systematics, Hangzhou Normal University, China. A second paratype of protargolstained specimens is deposited in the Natural History Museum, London, UK with registration number 2006:6:20:1.

Dedication: We dedicate this new species to Prof. Dr. Weibo Song, Director of Laboratory of Protozoology, Ocean University of China, Qingdao, China, in acknowledgement of his outstanding contributions to the study of ciliated protozoa in China.

Type locality: Freshwater pond, Lishui Street, Wenzhou, China (N 28°20.418’; E 120°43.817’).

Ecological data: Freshwater, water temperature 22.4 o C, pH 7.34.

Description: The zooid is bell-shaped, in vivo 170–285 μm long and 110–190 μm wide; length to width ratio of the fully extended zooid was 1.30–1.85. The peristomial lip is much wider than greatest body width, thick, and invariably reflected aborally. The peristomial disc is large, dome-shaped, and conspicuously elevated above the peristomial lip ( Figs. 1 , 11 ). Contracted zooids are ovoid or dumbbell-shaped ( Figs. 6 a,b, 15) with several conspicuous folds, usually numbering 3–4 adoral to the aboral ciliary wreath and 2–3 between the aboral ciliary wreath and the scopula ( Figs. 6 a,b, 12, arrowhead). The pellicle appears smooth at low magnification but fine, reticulate striations are visible at higher magnifications ( Figs. 5 , 30 ). Colonies without macrozooids.

The cytoplasm is grey or colourless, containing many large food vacuoles 13–40 μm in diameter ( Figs. 1, 6 b, 11–15). There is one contractile vacuole, ca. 29–37 μm in diameter, located on the dorsal wall of the infundibulum slightly aboral to the peristomial disc ( Figs. 1 , 11 ). The thick, C-shaped macronucleus is transversely oriented and located in the mid-body region ( Figs. 1 , 18 , 33 ); the micronucleus lies near the midregion of the macronucleus ( Figs. 1 , 33 , arrow).

The stalk is transparent or translucent, dichotomously branched, and slender, with a main trunk measuring approximately 500 μm long and 9 μm in diameter and zooid-bearing branches measuring 400–500 μm long and 10 μm in diameter ( Figs. 3 , 20, 21 ). The stalk surface is smooth. In culture, colonies usually contained only one or two zooids, occasionally four, rarely eight or more ( Fig. 3 ).

Zooids are very sensitive to stimuli and readily detach from the stalk to become free-swimming by means of their prominent oral cilia ( Figs. 4 , 14, 16, 17 ); free-swimming zooids usually have several pellicular folds ( Figs. 4 , 14 , arrowhead). The telotroch is cylindrical, measuring approximately 220 × 120 μm in vivo, with a conical posterior and domed-shaped anterior protuberance ( Figs. 2 , 19 ). Detached zooids can transform into telotrochs.

The haplokinety and polykinety of the peristomial infraciliature make approximately one and one-quarter circuits (450o) around the peristome before plunging into the infundibulum, where they make a further complete circuit ( Fig. 10 ). The haplokinety and polykinety at the peristomial region are folded after protargol impregnation ( Figs. 10 , 25, 31 ). This folding is almost certainly a consequence of the extremely broad peristome being compacted into the restricted confines of the peristome proper when the organism contracts. There are three infundibular polykineties, each consisting of three rows of kinetosomes. The adstomal ends of the three rows of infundibular polykinety 1 (P1) terminate at the same level while those of P2 terminate at different levels, the kinetosome row next to P3 being the shortest, and the one next to P1 the longest ( Figs. 8, 9 , 26, 27 ). The latter sometimes has a short, additional branch ( Figs. 9 , arrow, 27, arrow). The row of P3 farthest from P2 (outer row) is shorter than the other two rows ( Figs. 8 , arrowhead, 9, arrowhead). The outer two rows of P3 join together approximately 1/3 of the way from their abstomal to adstomal ends. The inner row of P3 terminates adstomally either at the same level as the outer two ( Fig. 8 , double arrowhead) or above the outer two at about the same level as the outer row of P2 ( Fig. 9 , double arrowhead).

The haplokinety passes around the infundibulum on the wall opposite to the infundibular polykineties. The germinal kinety (G) is relatively long, lying adoral to and parallel to the haplokinety and terminates adstomally slightly above the adstomal end of the haplokinety ( Figs. 10 , 26, 27 ). The aboral ciliary wreath (ACW) of the zooid consists of two staggered rows of kinetosomes (dikinety) that encircle the cell at approximately 1/3 of the distance between the scopula and the peristome ( Figs. 7 , arrow, 35, arrow). The ACW is significantly broader in the telotroch because of the proliferation of kinetosomes to form a polykinety ( Figs. 32, 34 , arrow).

The silverline system is reticulate, consisting of both transverse and longitudinal silverlines ( Figs. 5 , 30 ). The transverse silverlines in the oral region of the cell are more widely spaced than those in the aboral region ( Fig. 5 ). The ACW is represented by two parallel silverlines ( Figs. 5 , 30 , arrow). There are 125–145 transverse silverlines between the peristome and the ACW and 70–80 between the ACW and the scopula ( Fig. 5 ). The vertical silverlines are irregularly spaced ( Fig. 30 ). No pellicular pores associated with silverlines were observed. The scopula is the most argentophilic part of the cell ( Fig. 37 ).

There are two main kinds of myonemal fibers in Pseudepistylis songi , the longitudinal fibers and the circular fibers, both of which comprise several morphological subtypes. The longitudinal and circular fibers are interconnected to form a single, complete myoneme system.

Longitudinal fibers: Three types of longitudinal fiber can be recognized: long longitudinal fibers (LLF), short longitudinal fibers (SLF) and peristomial longitudinal fibers (PLF) ( Figs. 7 , 22–24, 28, 29 ). The LLF are less numerous, more diffuse, and more slender than the other two types of longitudinal fibers and extend throughout the entire length of the zooid ( Figs. 7 , 28, 29 ). The SLF are the most densely packed and thickest in diameter of the three types and are confined to the region between the PLF and the adoral one third of the zooid ( Figs. 7 , 29 ). The PLF are also densely packed, being intermediate in thickness between the other two types, and are confined to the region of the peristomial lip ( Figs. 7 , 22–24, 29 ). All three types of longitudinal fibers branch and interconnect with nearby fibers, thus forming a complete, anastomosing, meshlike network ( Figs. 7 , 28, 29 ).

Circular fibers: Three types of circular fibers were observed in the oral region of the cell. From outermost to innermost these are: peristomial ring fibers (PRF), central ring fibers (CRF), and peristomial disc fibers (PDF) ( Figs. 7 , 22–25, 29 ). The PRF consists of approximately 10 individual circular fibers located within the peristomial lip ( Figs. 7 , 22–24, 29, 36 ). The CRF comprises several circular fibers that combine to form a conspicuously thickened fiber located in the adoral part of the cell and connecting to the adoral ends of the PLF ( Figs. 7 , 22–25, 29 ). It appears that contraction of the CRF causes the peristomial disc to elevate when the zooid contracts ( Figs. 13 , 24, 25 ). The PDF are relatively inconspicuous, short, bundles ( Figs. 23, 24 ).

Figures

FIGURES 1 – 7. Pseudepistylis songi n. sp. in vivo (1 – 4, 6), protargol impregnation (7), silver nitrate impregnation (5). 1. Typical zooid; arrow indicates micronucleus. 2. Telotroch. 3. Colony of eight zooids showing both extended and contracted states as well as structure of stalk. 4. Detached zooid; arrowheads mark pellicular folds. 5. General silverline system; arrows indicate aboral ciliary wreath. 6. Zooids at low magnification, showing varieties of body shape when contracted; arrowheads mark pellicular folds. 7. Myoneme system; arrows indicate aboral ciliary wreath. Abbreviations: CRF, central ring fibers; LLF, long longitudinal fibers; PDF, peristomial disc fibers; PLF, peristomial longitudinal fibers; PRF, peristomial ring fibers; SLF, short longitudinal fibers. Scale bars: 100 μm (Fig. 1), 600 μm (Fig. 3).

FIGURES 8 – 10. Infraciliature of oral apparatus of Pseudepistylis songi n. sp. following protargol impregnation. 8. Typical arrangement of three infundibular polykineties showing the short outer row of P 3 (arrowhead) and the inner row of P 3 (double-arrowhead). 9. An alternative arrangement of the three infundibular polykineties showing the short outer row of P 3 (arrowhead), the shorter inner row of P 3 (double-arrowhead) and the short additional branch of P 2 (arrow). 10. General infraciliature of the oral apparatus. Abbreviations: F, filamentous reticulum; G, germinal kinety; H, haplokinety; P 1 – P 3, infundibular polykineties 1 – 3; Po, polykinety (peristomial continuation of P 1).

FIGURES 11 – 21. Pseudepistylis songi n. sp. in vivo. 11. Typical zooid. 12, 15, 18. Contracted zooid. 13, 14, 16, 17. Detached zooid. 19. Telotroch. 20. Stalk. 21. Newly divided zooids and stalk. Arrow in 11 indicates contractile vacuole; arrowheads in 12 and 14 indicate pellicular folds; arrows in 12 and 15 indicate food vacuoles; arrow in 13 indicates peristomial disc; arrow in 18 indicates macronucleus; arrow in 19 indicates aboral ciliary wreath. Scale bars: 100 μm (Fig. 11), 300 μm (Fig. 20).

FIGURES 22 – 37. Pseudepistylis songi n. sp. protargol (22 – 29, 31 – 37) and silver nitrate (30) impregnation. 22, 25. Typical zooid. 23, 24. Peristomial disc and myonemal fibers. 26, 27. Infraciliature of oral apparatus. 28, 29. Myoneme system. 30. Pellicular striae. 31. Haplokinety and polykinety. 32, 34. Aboral ciliary wreath of telotroch. 33. Zooid showing macronucleus and micronucleus (arrow). 35. Aboral ciliary wreath of typical zooid. 36. Oral fiber. 37. Scopula. Arrows in 30, 32, 34, 35 indicate aboral ciliary wreath. Abbreviations: CRF, central ring fibers; F, filamentous reticulum; G, germinal kinety; H, haplokinety; LLF, long longitudinal fibers; P 1 – P 3, infundibular polykineties 1 – 3; PDF, peristomial disc fibers; PLF, peristomial longitudinal fibers; Po, polykinety (peristomial continuation of P 1); PRF, peristomial ring fibers; SLF, short longitudinal fibers. Scale bars: 50 μm (Fig. 25).

Tables

TABLE 1. Morphological characterization of Pseudepistylis songi n. sp. (all measurements in μm).

Character	n	Min	Max	Mean	SD	SE	CV (%)
Length of zooid, in vivo	18	170	285	220	31.90	7.74	14.5
Width of zooid, in vivo	18	110	190	140	22.91	5.56	16.3
Width of peristomial disc, in vivo	18	150	230	180	22.51	5.46	12.4
Length of zooid, protargol-impregnated	24	106	197	151.3	29.06	6.06	19.2
Width of zooid, protargol-impregnated	24	86	207	131.9	31.29	6.52	23.7
Width of peristomial disc, protargol-impregnated	24	56	131	91.4	17.13	3.57	18.7
Number of silverlines from peristome to ACW	13	125	145	136.6	7.49	2.16	5.5
Number of silverlines from ACW to scopula	13	70	80	76.6	2.66	0.77	3.5