Pleuronema setigerum Calkins, 1902

Pan, Xuming, Huang, Jie, Fan, Xinpeng, Ma, Honggang, Al-Rasheid, Khaled A. S., Miao, Miao & Gao, Feng, 2015, Morphology and Phylogeny of Four Marine Scuticociliates (Protista, Ciliophora), with Descriptions of Two New Species: Pleuronema elegans spec. nov. and Uronema orientalis spec. nov., Acta Protozoologica 54 (1), pp. 31-43 : 36-37

Pleuronema setigerum Calkins, 1902 ( Figs 3 I–M ;

Table 1 )

Since first reported, this species has been rede- scribed on four occasions ( Kahl 1931, Noland 1937, Borror 1963, Pan et al. 2010). Some new characters were found in the Shenzhen population and hence an improved diagnosis of this species is supplied here based on both previous and present studies.

Improved diagnosis: In vivo 25–50 × 10–30 μm in size, slender oval in outline; buccal field occupying four-fifths of body length; about 9–13 prolonged caudal cilia; three to five preoral kineties and 12–22 somatic kineties; M1 about 20% of the anterior part of M2a in length, consisting of three longitudinal rows of basal bodies; posterior end of M2a ring-like; contractile vacuole subcaudally positioned; one macronucleus; marine habitat.

Description of the Shenzhen population: In vivo 25–40 × 10–20 µm, slender oval in outline, widest at mid-body ( Fig. 3I ). Ventral side almost flat, dorsal side convex. Buccal field cavity about four-fifths of body length ( Fig. 3I ). Extrusomes 3 μm long, lying beneath notched pellicle and closely arranged between ciliary rows ( Fig. 3J ). Cytoplasm colourless to slightly grayish, containing many shining globules of varying size (3–5 μm across), food vacuoles (4–6 μm across) and irregularly-shaped crystals (mostly 3–4 μm across) ( Fig. 3I, J ). One spherical macronucleus, about 16 × 15 µm, located in anterior 1/3 of cell, usually with many globular nucleoli. Single contractile vacuole about 10 µm in diameter, located subcaudally near dorsal cell margin ( Fig. 3K ). Somatic cilia about 8 µm long ( Fig. 3I ). About thirteen prolonged caudal cilia, each about 20 µm in length ( Fig. 3K ).

Swims moderately fast while rotating about main body axis, sometimes drifting or lying motionless on debris for short periods ( Fig. 3M ).

Twelve to 14 somatic kineties, composed of paired basal bodies in anterior three-quarters of the body and monokinetids in the posterior quarter, extending almost the entire length of the cell ( Fig. 3M ). Five or six preoral kineties to left of buccal field.

Oral apparatus typical for genus: M1 with one short and two longer rows of basal bodies; M2a mostly two-rowed but with a middle section that is single-rowed in a ‘zigzag’ pattern, with its posterior end characteristically ring-like ( Fig. 3L ). M2b V-shaped, distinctly separated from M2a; M3 three-rowed ( Fig. 3M ). Paroral membrane about 80% of cell length.

Comparison and remarks: Pleuronema setigerum was first reported by Calkins in 1902 and then rede- scribed by Kahl (1931) who cited Calkins’s drawing. Borror (1963) described its infraciliatrue but gave only a diagram of the buccal morphology, then Small (1964) provided a detailed line drawing based on Borror’s protargol stained specimen. Pan et al. (2010) redescribed this form and provided an improved diagnosis based both on the Qingdao population and the previous studies. The Shenzhen population is very similar to the previous ones in both living and infraciliature data, except for having a smaller body size (25–40 × 10–20 µm vs. 30–50 × 15–30 µm), fewer somatic kineties (12–14 vs. 14–22) and more preoral kineties (five or six vs. three or five). We consider these variations to be populationdependent, and thus treat the Shenzhen population as conspecific with other populations of P. setigerum .

Figures

Fig. 3.Pleuronema grolierei Wang et al., 2008 (A–H) andP. setigerum Calkins, 1902 (I–M) in vivo (A–D, I–K) and after protargol (E–H, L, M). A, I – ventral views of typical individuals, arrow in (A) shows contractile vacuole, arrowheads in (I) mark paroral membrane; B – ventral view, arrowheads mark oral cilia; C, K – ventral views, arrowheads point to caudal cilia; D – ventral view, arrow marks ingested algae, arrowhead shows irregularly-shaped crystals; E – anterior region, arrow shows the anterior part of membranelle 2; F – detailed structure of the buccal area; G – posterior region, arrowhead points to membranelle 3; H – macronucleus; J – ventral view, arrowheads show irregularly-shaped crystals; L – posterior region, arrowhead indicates the ring-like posterior end of M2a; M – detailed structure of the buccal area, arrow marks membranelle 3, arrowheads show preoral kineties. M1 – membranelle 1; M2a – the anterior part of membranelle 2; M2b – the posterior part of membranelle 2; Ma – macronucleus. Scale bars: A, I = 20 μm, M = 5 μm.