Frontonia multinucleata n. sp.

(Figs. 4–6; Table 1)

Diagnosis: marine Frontonia in vivo 70–120 × 40–75 µm, dorsoventrally flattened about 2:1. 58–67 somatic, 3 vestibular and 4–5 postoral kineties. 3 peniculi each with 4 kineties. 2–4 globular macronuclear nodules. Single contractile vacuole located in posterior 1/3 of cell length.

Type location: A clear sandy beach (salinity 30 ‰) of Qingdao, China.

Type slides: One holotype with silver nitrate impregnated specimens (slide number: 2007:5:17:2) is deposited in the Natural History Museum, London, UK, and one paratype (slide number: 2006060101-2) is deposited in the Laboratory of Protozoology, Ocean University of China.

Etymology: This species is the first one in Frontonia which has more than one macronucleus (2–4). Thus, it is named according to this character: multi- (many), nucleata.

Description: Size in vivo about 70–120 × 40–75 µm. Cell shape rather constant, ellipsoidal in outline when viewed from ventral side (Figs. 4 A, 4B; 5A, 5D). Dorsoventrally flattened about 2:1. Extrusomes spindle-shaped, about 8 µm long (20–25 µm long after being ejected, Fig. 5 B), densely arranged in cortex (Figs. 4 A, 4B; 6C). Somatic cilia about 8 µm long. Cytoplasm colorless or grayish, often full of tiny granules, especially in caudal part (Figs. 4 A, 4B; 5A, 5D). In all specimens observed from the culture which maintained for about 2 weeks, macronuclear nodules always in 2–4, yet mostly 4, generally globular in shape and about the same size, grouped or sparsely distributed (Figs. 4 A, 4B, 4G, 4I; 6B, 6E, 6F). One large contractile vacuole located in posterior 1/3 of cell length, ca. 15 µm in diameter (Figs. 4 A, 4B, 4E, 4J; 5E).

Movement mainly by gliding back and forth on substrate; when swimming, moderately rapid with rotation around the long axis of the cell.

Infraciliature as shown in Figs. 4 I–K. Both anterior and postoral sutures conspicuous, which extend onto dorsal side (Fig. 4 C, 4I, 4J). On average 63 somatic kineties; 4–5 postoral kineties (PK, Figs. 4 H, 4I, 4K; 6N); 3 vestibular kineties, conspicuously short (Figs. 4 H, 4I, 4K; 6J, 6L). Single CVP right dorsally located, at approximately posterior 1/3 of cell length (Figs. 4 C; 6G, 6K).

Triangular buccal cavity occupying about 1/5 of body length. Peniculus 1–3 about equally long, all with 4 kineties; among them, P3 curved to right whose length becomes conspicuously shorter from right to left (Figs. 4 F, 4H, 4I, 4K; 6D, 6H). Double-rowed paroral membrane on right side of buccal cavity (Figs. 4 H, 4I, 4K; 6L). Argentophilic line positioned parallel to paroral membrane (Fig. 4 H). Silverline system as quadrangular cortical meshes (Fig. 6 I).

Comparison: Frontonia multinucleata n. sp. is the only one among members of the genus, which has consistently several macronuclear nodules (vs. single in all other known congeners). Hence, the new species is easily recognizable (Fig. 10 C, 10D, 10I, 10J, 10K, 10M, 10N, 10R, 10S; Table 2).