Epistylis unioi Gong, 1986

Li, Ming, Li, Weidong, Ge, Xianping, Wang, Chong, Zhang, Lin, Huang, Feng & Liu, Huiyu, 2012, First report of Epistylis unioi Gong 1986 (Sessilida: Epistylididae) infecting fry of Pelteobagrus fulvidraco in Hubei, China, Zootaxa 3556, pp. 80-88 : 81-86

Epistylis unioi Gong, 1986

( Table 1 and Figs. 1–5)

Host: Fry of Pelteobagrus fulvidraco .

Type locality: freshwater; Honghu Lake Fish Hatchery, Hubei Province, China, with water temperature of 22? and pH 6.85.

Deposited specimens: Slides 2010W001-006 of protargol-stained specimens, slides 2010W007-010 of silver nitrate-impregnated specimens have been deposited in Hubei Key Laboratory of Animal Nutrition and Feed Science, Wuhan Polytechnic University, China.

Description: Zooid is elongated and somewhat vase-like in shape, tapering gradually from the peristome disc to aboral end when fully expanded and measuring 56–88 (68) µm×22–38 (30) µm in vivo (Fig. 1c). Ratio of length to width is 1.7–3.2 (2.3):1, with maximum width at peristomial lip, 27–45 (35) µm in diameter. Peristomial disc is broad, flattened and slightly obliquely elevated in expanded individual (Figs. 2b and 4). The peristomial lip is so contractile that it can cover the adoral cilia and peristomial disc completely and put them into the body (Fig. 2c). Pellicle appears smooth at low magnification, with fine transverse striations detectable of 400× and higher, especially in SEM and silver nitrate specimens (Figs. 2d and 3a). The cytoplasm is colorless to slightly greyish, usually containing numerous food vacuoles (3–5 µm in diameter) in the anterior and mid-body region (Figs. 1c, d and 4). One contractile vacuole is apically located slightly below the peristome disc and around the infundibulum, measuring 5–10 µm in diameter (Figs. 1c and 4). The macronucleus is conspicuous and horseshoe-shaped, always transversely situated at the foreside of the body (Fig. 4).

Colony is asymmetrically and dichotomously branched, usually with only two levels of branches. Zooids are situated in pairs, numbering 2–4 per colony (Fig. 1d). Terminal stalks are unequal in length, while the primary stalk is quite short. Its ringlike base adheres to the body surface, secreting adhesive material and causing obvious skin lesions (Figs. 2e and f).

Haplokinety (H) and polykinety (Po) form a distinct spiral going counterclockwise and make approximately one and a half turns aroud peristome disc. Then, all of them extend into the infundibulum, where they make a further turn (Figs. 3b, c and d). One short kinetal fragment is visible near distal end of haplo- and polykinety (Fig. 3b). Polykinety forms three peniculi in lower half of vestibulum, each consisting of three kineties (Figs. 3b, c and 5). Peniculus 1 (P1) and 2 (P2), much longer than peniculus 3 (P3). Adstomal ends of the three rows of P1 terminate at the same levels. Row 2 and 3 of P2 are shorter than row 1. P2 and P3 terminate adstomally at the same level, above the adstomal ends of P1 (Fig. 5). Haplokinety passes around vestibulum on opposite wall to peniculi. Germinal kinety (G) parallels haplokinety within the upper half of vestibulum (Figs. 3b and 5). Epistomial membrane (EM) is short, located near upper level of vestibulum (Figs. 3c and 5). Aboral trochal band (TB) consists of two staggered rows of kinetosomes, encircling cell in posterior region and measuring 13.2–24 (19.5) µm in diameter (Figs. 3a–c and 4). The distance between TB and peristome is 20.4–28.8 (24.6) µm compared to 12.0–24.2 (16.2) µm between TB and scopula.

FIGURE. 1 Light microscopic images of E. unioi in vivo. a–b Numerous epistylids occurred all over the baraels (a) and gills (b) of the fry of Pelteobagrus fulvidraco . Scale bar in a =100 µm and b =50 µm. c A typical zooid in vivo. Scale bar=10 µm. d Entire colony, dichotomously branched, usually with only two levels of branches. Scale bar=30 µm.

FIGURE. 2 SEM images of E. unioi . a Overview of the ciliates, occurring over the body surface of fish fry. Scale bar=10 µm. b Extended zooid, showing the adoral cilia and peristomial lip. Scale bar=5 µm. c Contracted zooid, showing the peristomial lip. It is so contractile that it can cover the peristomial disc completely. Scale bar=5 µm. d Pellicle of E. unioi , showing many sparsely distributed pellicular pores (arrowhead) associated with pellicular striations (arrow). Scale bar=2 µm. e Primary stalk (st), showing its ringlike base (arrow) adhering to the body surface of fish and secreting adhesive material (am). Scale bar=5 µm. f the stalk (st), causing obvious skin lesions (arrow) on the host. Scale bar=2 µm.

Silverline system consists of 37–45 (41.2) pellicular striations between peristome and TB, and of 26–33 (29.1) between TB and scopula, with an average distance between adjacent silverlines of 0.5 µm (Figs. 2a and 3a). Many sparsely distributed pellicular pores associated with pellicular striations can be observed (Fig. 2d).

Detailed morphometric parameters of E. unioi in our present study are presented in Table 1 .

In addition, the telotrochs of E. unioi were also observed in our work (Figs. 3e and f). The zooid destined to become a telotroch stops feeding activities and contracts. Structures such as the peristomial disc, oral cilia are then covered by the peristomial lip. The lower half contracts progressively, with its stalk being absent gradually. And the upper half folds over the contracted lower part, the whole structure becoming much shorter, broader and somewhat column-like in shape. It has a distinct wreath of locomotor cilia forming at trochal band and beating strongly.

FIGURE. 3 Light microscopic images of E. unioi stained with silver nitrate (a, e), and protargol (b–d, f). a Specimens stained with silver nitrate, showing transverse striations over the pellicle. Scale bar=10 µm. b–c–d Specimens stained with protargol, showing oral infraciliature: the distal kinetal fragment (arrow), epistomial membrane (EM), germinal kinety (G), haplokinety (H), polykinety (Po) and infundibular polykineties 1–3 (P1–3); trochal band (TB), scopula (Sc) and macronucleus (Ma). Scale bar in b–c–d =10 µm. e Telotroch of E. unioi stained with silver nitrate, showing the distinct wreath of locomotor cilia forming at trochal band (arrow). Scale bar=10 µm. f Telotroch of E. unioi stained with protargol, showing its oral infraciliature and trochal band (arrow). Scale bar=10 µm.

FIGURE. 4 Schematic drawing of E. unioi , showing the general form and structures: peristomial disc (PD), peristomial lip (PL), cytopharynx (Cy), contractile vacuole (CV), macronucleus (Ma), food vacuole (FV), trochal band (TB), scopula (Sc) and stalk (St). Scale bar=10 µm.

FIGURE. 5 Schematic drawing of oral infraciliature, showing the distal kinetal fragment (arrow), epistomial membrane (EM), germinal kinety (G), haplokinety (H), polykinety (Po) and infundibular polykineties 1–3 (P1–3).

Measurements in µm; Min minimum, Max maximum, Mean arithmetic mean, SD standard deviation, CV coefficient of variation, N number of individuals investigated.

Tables

TABLE 1. Morphometric light microscopic characterization of E. unioi.

Character	Min	Max	Mean	SD	CV	N
Length of zooid, in vivo	56.4	88.2	68.0	9.1	13.4	20
Width of zooid in, vivo	22.3	37.7	29.8	4.0	13.5	20
Ratio of length to width of zooid, in vivo	1.7	3.2	2.3	0.4	18.7	20
Length of zooid, protargol	33.6	52.8	40.8	5.5	13.5	20
Width of zooid, protargol	15.6	26.4	22.2	2.8	12.5	20
Diameter of peristomial lip, in vivo	26.5	44.9	35.4	4.7	13.6	20
Diameter of oral apparatus, protargol	12.0	21.6	18.1	2.3	12.7	20
Diameter of trochal band (TB), protargol	13.2	24.0	19.5	2.9	15.1	16
Width of scopula, protargol	3.6	4.8	4.5	0.4	9.3	10
Distance from TB to peristome, protargol	20.4	28.8	24.6	2.7	10.9	12
Distance from TB to scopula, protargol	12.0	24.2	16.2	3.2	19.8	12
Number of silverlines from TB to peristome, silver nitrate	37	45	41.2	2.4	5.8	9
Number of silverlines from TB to scopula, silver nitrate	26	33	29.1	2.2	7.7	9