Frontonia ocularis Bullington, 1939

Pan, Xuming, Liu, Weiwei, Yi, Zhenzhen, Fan, Xinpeng, Al-Rasheid, Khaled A. S. & Lin, Xiaofeng, 2013, Studies on Three Diverse Frontonia Species (Ciliophora, Peniculida), with Brief Notes on 14 Marine or Brackish Congeners, Acta Protozoologica 52 (1), pp. 35-49 : 40-42

Frontonia ocularis Bullington, 1939 ( Figs 2 , 3 ; Tables 1, 2)

The original definition of this organism was based only on live specimens and no information about its infraciliature was previously available ( Bullington 1939). Based on data from both the present and previous studies, an improved diagnosis is presented here, including a description of its infraciliature.

Improved diagnosis: Marine or brackish Frontonia , about 115–140 × 50–75 μm in vivo, reniform with anterior end broad and posterior end slightly narrowed, right margin depressed in anterior 1/3 of body; length to width ratio about 2:1; small buccal field about 15 to 20% of body length; a prominent pigment on right side of anterior extremity; about 93–107 somatic kineties; three vestibular and three or four postoral kineties; peniculi 1 and 2 each with four rows, peniculus 3 with two rows; macronucleus ellipsoidal, located in central region of body; two contractile vacuoles located right-ventral, one in anterior half and the other in posterior half of body.

Description of Zhuhai population: Body 115–120 × 50–60 µm in vivo, reniform with anterior end broad and posterior end slightly narrowed, right margin depressed in anterior 1/3 of body ( Figs 2A, C , 3A, C ). Ratio of length to width between 2:1 and 3:1 ( Figs 2A , 3A ). Dorsoventrally flattened about 3:2. Buccal cavity about 20 × 10 µm, occupying 15 to 20% of body length ( Fig. 3D, F ). Cytoplasm slightly grayish, often with many large (8–10 µm across), black granules at posterior end of body ( Fig. 2A ). Many dark-green food vacuoles and small, blue crystal granules (1–2 µm) distributed randomly in cytoplasm ( Fig. 2A ). Brown-black pigment spot usually present on extreme right border near anterior end of body ( Figs 2A , 3A, B, K ). Extrusomes spindle-shaped, about 4 µm long but, when extruded, about 15 µm long and rod-shaped with one end curved ( Figs 2D , 3K ). Macronucleus ellipsoidal, about 25 × 15 μm and located in mid-region of body ( Fig. 2A ). No micronucleus observed. Two contractile vacuoles 7–10 µm in diameter, located right-ventrally, one each in anterior and posterior 1/3 of body respectively ( Figs 2B , 3B ). Somatic cilia about 6 µm long ( Fig. 3E ); cilia in caudal end longer than others, about 8 µm long. Locomotion by revolving moderately rapidly on substrate or by swimming in water while rotating clockwise about the long body axis.

Somatic ciliature as shown in Figs 2E, F, G , 3G, I, J, M, O . About 93 to 107 somatic kineties shortened progressively both anteriorly and posteriorly from lateral side to oral area, forming conspicuous anterior and posterior sutures that extend from anterior end of buccal cavity over apical end of cell and onto dorsal side. Buccal structure as shown in Figs 2G , 3H, O . Three conspicuous peniculi located on left wall of buccal cavity: peniculi 1 and 2 about equal in length, positioned close to each other parallel to edge of left vestibular wall, slightly curved to right at anterior ends and each composed of four rows of kinetosomes ( Figs 2G , 3H ). Peniculus 3 composed of two kinety rows which are about equal in length. Paroral membrane double-rowed, located on right side of buccal cavity ( Figs 2G , 3H ). Three vestibular kineties extending along the paroral membrane, each composed of densely arranged dikinetids. Three or four postoral kineties ( Fig. 2G ). Several argentophilic lines left of paroral membrane ( Fig. 3N ).

Comparison and remarks: The population studied here corresponds very well with the original description ( Bullington 1939) in terms of body shape, the prominent pigment spot in the anterior border, the number and location of the contractile vacuoles, and the manner of spiralling when swimming forwards. Hence, the identification of this species is not in doubt. Compared with previous descriptions of F. ocularis , our population has a smaller body size (about 120 × 55 µm vs. about 141 × 76 µm) and the prominent pigment spot is brown-black, whereas it is cited as being reddish-brown in earlier descriptions ( Bullington 1939). However, we consider these dissimilarities to be population-dependent.

SSU rRNA gene sequence: The SSU rRNA gene sequence of Frontonia ocularis Bullington, 1939 has been deposited in the GenBank database with accession number, length, and G+C content as follows: FJ868198, 1746 bp, 44.73%.

Figures

Fig. 2. Frontonia ocularis in vivo (A–D) and after protargol impregnation (E–G). A – ventral view of a typical individual; B – ventral view showing position of contractile vacuoles; C – different body shapes; D – extruded extrusomes; E, F – infraciliature in ventral and dorsal views, macronucleus, and contractile vacuole pore; G – infraciliature of the buccal area. CV – contractile vacuole, CVP – contractile vacuole pore, Ma – macronucleus, P1–P3 – peniculi 1, 2, 3, PM – paroral membrane, PK – postoral kineties, VK – vestibular kineties. Scale bars: A = 60 μm, E, F = 40 μm.

Fig. 3. Frontonia ocularis in vivo (A–F, K, L) and after silver carbonate (I, N) and protargol impregnation (G, H, J, M, O). A – ventral view of a typical individual, arrow shows the black brown pigment spot; B – ventral view, to show two contractile vacuoles (arrowheads), arrow shows the prominent brown pigment spot; C – different body shapes; D, F – buccal area; E – posterior part of cell, arrowheads mark caudal cilia; G, H, N – detailed structure of buccal area, arrowhead (G) marks paroral membrane, arrow (N) shows argentophilic line; I – part of argyrome; J, O – anterior suture (arrowheads in J) and postoral suture (arrowheads in O); K – extrusomes (arrowheads) forming distinct seam underneath cortex, arrow shows the black brown spot; L – extruded extrusomes; M – ventral view to show closely arranged somatic kineties. P1–P3 – peniculus 1, 2, 3. Scale bars: A, B = 50 μm, C = 80 μm.