Paradiophrys irmgard ( Mansfeld, 1923 ) Jankowski, 1978

Paradiophrys irmgard ( Mansfeld, 1923) Jankowski, 1978

Description. Only several protargol-stained specimens are available, which still allows for the identification of species. Cell size 67–90 × 42–68 μm after protargol staining, elongate rectangular in outline ( Fig. 3 View FIGURE 3 ). Adoral zone of membranelles occupying 55–60% of body length, divided into two parts and composed of 33–36 membranelles: about six membranelles in apical part, positioned on dorsal side and widely arranged; the remaining on ventral side; kinetosomal structure typical of euplotid ( Fig. 3A, C, G View FIGURE 3 ). Undulating membranes composed of paroral and endoral membranes, which are of about the same length, spatially intersecting ( Fig. 3A, G View FIGURE 3 ), but the detailed structure undetermined. Somatic ciliature basically stable. Nine or ten relatively weak frontoventral cirri, about 30 μm long, sparsely distributed throughout the frontal region; one of them located close to and ahead of transverse cirri ( Fig. 3A, C, H View FIGURE 3 ). Invariably, there are five transverse cirri, with the left four cirri markedly large, and the rightmost one rather small, aligned transversely; the cilia about 50 μm long ( Fig. 3A, C, I View FIGURE 3 ). Two or three left marginal cirri shifted posteriorly when compared to members of the genus Diophrys ( Fig. 3A, C, F View FIGURE 3 ). Invariably three caudal cirri on dorsal side of right cell margin, prominent because of hook-like ( Fig. 3B, C, J View FIGURE 3 ). Constantly six dorsal kineties on dorsal side, with 17–20, 26–28, 21–25, 24–28, 21–22, and 14–17 dikinetids (counted from left to right), respectively; all kineties dikinetidal, closely spaced at the anterior end and loosely spaced at the posterior end, and conspicuously shortened posteriorly except the second one, which is the longest and extends to the rear end of cell ( Fig. 3B D View FIGURE 3 ); only the anterior basal body of each dikinetid bearing a 4 μm long cilium. Invariably two ellipsoidal macronuclear nodules, 18–20 × 8–10 μm, which are connected by a thin fiber ( Fig. 3B, E View FIGURE 3 ); micronucleus not observed in preparations. Fine cortical granules densely aligned in rows along dorsal kineties on dorsal side (not shown).

Ecological data. Water temperature 27.6 ºC, pH 8.2, salinity 32.8‰, DO 7.6 mg /L.

Morphological comparison. This species was originally described by Mansfeld (1923) under the name Diophrys irmgard , which was transferred to the newly erected genus Paradiophrys by Jankowski (1978). Hill and Borror (1992) first studied several USA isolates of Paradiophrys irmgard using the protargol staining method, which revealed considerable variability in body size, and the number and distribution of frontoventral cirri and transverse cirri ( Table 3 View TABLE 3 ), but relatively minor difference in cell shape and the arrangement of left marginal cirri and dorsal kineties among populations. Song et al. (2007) redescribed it as Diophrys irmgard and provided morphometric data based on a China population, compiled in the monograph by Song et al. (2009). The present form investigated is very similar to type population in body shape and size after fixation, the number and the positioning of cirri, especially left marginal cirri, so it can be identified as Paradiophrys irmgard , a new record for Japan. With regards to ciliature, the present form is very similar to Qingdao and USA populations in: (i) the number of adoral membranelles (33–36 vs. 25–39); (ii) posteriorly shifted left marginal cirri; and (iii) constantly two macronuclear nodules and six dorsal kineties. Nevertheless, minor differences exist among these isolates in terms of the numbers of frontoventral cirri and transverse cirri as well as left marginal cirri, variable characters commonly recognized within some species of Diophrys -complex ( Song et al. 2007; Hu 2008; Jiang et al. 2011; Luo et al. 2014). Hill and Borror (1992) did not provide the details of paroral and endoral membranes, but described ‘a monokinetid endoral row of cilia and a large polykinetid paroral membrane extend from the cytostome anteriorly along the right edge of the buccal overture’, inferring that both are equal long as shown in Paradiophrys multinucleata and Diophrys species; according to the illustrations, it may occupy about 3/4 of the length of buccal field. Therefore, all these divergences discussed above could be accepted as intraspecific variation. Song et al. (2007) recorded an extremely reduced endoral membrane in their form, which might represent a distinct species in the genus. However, as regards its high similarity with populations of P. irmgard reported previously and in this study, it might be conservatively considered as a population of the species.

Within Paradiophrys , only three congeners can be compared with the Nagasaki population of Paradiophrys irmgard ( Table 3 View TABLE 3 ). P. kahli ( Dragesco, 1963) Jankowski, 1978 has only been described once without details of the ciliature ( Dragesco 1963), but can be distinguished from P. irmgard by its unsculptured surface, small buccal field, slender body shape, and most frontoventral cirri clustered together right of buccal field as well as single caudal cirrus. P. multinucleata ( Hartwig, 1973) Jankowski, 1978 was first reported by Hartwig (1973) to have many macronuclear nodules clustered. This species was later described to possess six frontoventral and four transverse cirri, 20-30 macronuclear fragments and a dorsal ridge along the right side of the cell ( Hill & Borror 1992), and thus cannot be confused with P. irmgard . The Nagasaki isolate of P. irmgard differs from Paradiophrys zhangi Jiang et al., 2011 by more adoral membranelles (33–36 vs. 26–30), endoral membrane (nearly equal to paroral membrane vs. highly reduced, one-third of paroral membrane in length), more frontoventral cirri (9 or 10, sparsely arranged vs. usually 7, two-grouped), and more dikinetids (26–28 vs. 21, counted from illustration of holotype) in the second dorsal kinety ( Jiang et al. 2011).