Ancistrum japonicum Uyemura, 1937

Xu, Kuidong, Song, Weibo & Warren, Alan, 2015, Two New and Two Poorly Known Species of Ancistrum (Ciliophora, Scuticociliatia, Thigmotrichida) Parasitizing Marine Molluscs from Chinese Coastal Waters of the Yellow Sea, Acta Protozoologica 54 (3), pp. 195-208 : 202-203

Ancistrum japonicum Uyemura, 1937 ( Figs 18–25 ; Table 1)

Nomenclature: The species was originally described by Uyemura (1937), based on observations both of live observations and of specimens stained with Heidenhain’s haematoxylin, under the name Ancistruma japonica . The valid species name should be Ancistrum japonicum Uyemura, 1937 since Ancistruma Strand, 1926 is considered to be an objective synonym of Ancistrum Maupas, 1883 ( Raabe 1970). Other synonyms include: Ancistrumina japonica Uyemura, 1937 and Ancistrum japonicum ( Uyemura 1937) . The identification of this species is still con- fused despite a taxonomic revision of the group to which it belongs ( Raabe 1970). Furthermore, no type material exists. We suggest neotypification of Ancistrum japonicum with the specimens described in the present study which were isolated from the same host mollusc, namely Cyclina sinensis (Gmelin) , and from the same region ( East Asia) that the species was originally discovered.

Diagnosis of neotype: Size about 80 × 25 µm in vivo; body cuneate in lateral view, with anterior and posterior-dorsal ends both bluntly pointed. One ovoid macronucleus and one micronucleus. On average 20 somatic kineties, with both left and right kineties distinctly shortened in posterior region of cell. Buccal area extending to posterior pole and occupying on average 81% of body length. Membranelles 1 and 3 short, each composed of two or three rows of kinetosomes; membranelle 2 composed of two rows and occupying about 70% of body length.

Neotype host and site: Marine venus clam Cyclina sinensis (Gmelin) ; gills and mantle cavity.

Neotype locality: Marine culture beds at Rizhao on the Yellow Sea coast of northern China (35°40′N, 119°57′E).

Neotype material: A protargol slide with the neotype specimen circled in ink is deposited in the Laboratory of Protozoology , Ocean University of China with registration number RZ-950428-20. A paraneotype slide is deposited in the same collection with registration number RZ-950428-21.

Description (based on neotype specimens unless stated otherwise): Size in vivo 60–90 × 18–30 µm, usually about 80 × 25 µm with ratio of length to width about 3.3: 1; protargol-stained specimens on average 85 × 36 µm suggesting a slight body inflation during the fixation or staining process; strongly flattened bilaterally 3–4: 1 ( Table 1). Body more or less cuneate in lateral view with narrowly rounded anterior end and slightly protruded posterior-dorsal end; ventral margin convex, dorsal margin sigmoidal and convex in posterior quarter of cell ( Figs 20, 24 ). Specimens from Dosinia japonica (Reeve) slightly smaller and stouter than those from neotype population parasitizing Cyclina sinensis , usually 65–70 × 20–30 µm in vivo with ratio of length to width about 3:1; bilaterally flattened about 2–2.5: 1; body more or less distinctly concave in dorsal margin and prolonged dorsally in posterior region ( Figs 18, 19 ). Single macronucleus usually located in the mid- to anterior half of body, usually ovoid, occasionally near to triangular, about 26 × 16 µm in protargol-stained specimens. One globular micronucleus positioned anterior of macronucleus ( Fig. 25 ). Contractile vacuole located anterior of cytostome near ventral side, 5–8 µm across. Cortex flexible with cortical granules loosely arranged along ciliary rows. Cytoplasm usually hyaline in anterior half of body and opaque in posterior half due to accumulation of many food vacuoles, up to 8 µm across, and lipid droplets, about 5 µm across. Movement by rotation about main body axis with anterior and posterior ends frequently curved dorsally; cells can attach to substrate via anterior thigmotactic area ( Figs 18–20 ).

On average 20 (18–21) somatic kineties, equidistantly spaced, on average 10 (8–11) rows on each side; anterior third of kineties composed primarily of dikinetids, posterior two thirds composed mainly of monokinetids ( Figs 23–25 ). Somatic kineties mostly terminate at anterior end of body, except for several right-ventral preoral kineties which are progressively shortened anteriorly forming an imbricate structure; all kineties excluding SK1 distinctly shortened in posterior region of cell, forming a distinct glabrous zone on both left and right sides ( Figs 24, 25 ). Somatic cilia 10–15 µm long, anterior cilia very densely arranged and rigid forming a thigmotactic area.

Buccal field of typical pattern for genus, occupying about 81% of body length. Oral cilia about 15 µm long anteriorly, increasing to about 25 µm long posteriorly where they form a conspicuous brush-like structure ( Figs 20, 23 ). Membranelle 1 short, composed of two or three rows of kinetosomes; M2 hook-shaped, composed of two longitudinal rows often with several single-rowed kinetosomes anteriorly, occupying about two thirds of body length; M3 near end of M2, of similar length to M1, composed of 10 kinetosomes arranged in three oblique rows. Paroral membrane lies parallel to somatic kinety 1, composed of a zigzag file of dikinetids, extending beyond M1 anteriorly and terminating posteriorly near caudal pole. Cytostome at base of PM and M2, ellipsoidal in outline, connected with radially arranged fibers ( Fig. 21 ). Scutica (Sc) patch-like, close to caudal cilium complex (CCo) which bears a single caudal cilium about 20 µm long ( Figs 23–25 ).

Transverse silverlines very sparsely distributed between somatic kineties, in particular in mid-body; silverlines from right somatic kineties converge at posterior end; several longitudinal silverlines recognizable in buccal area. Single contractile vacuole pore (CVP) located near end of somatic kinety 2 ( Figs 21, 22 ).

Occurrence and prevalence: Ancistrum japonicum was first reported by Uyemura (1937) in large numbers in the mantle cavity of marine bivalves including Meretrix meretrix (L.), Paphia philippinarum Adams and Reeve , Cyclina sinensis (Gmelin) , Mactra veneriformis Reeve , Mactra sulcataria Reeve and Dosinia bilnulata Gray , in seas adjacent to Japan. This species was not subsequently reported until we recovered it from the venus clam Cyclina sinensis (with prevalence of 20/20 and light intensity of infestation) and likely also from the hard clam Meretrix meretrix (with prevalence of 20/22 and light intensity of infestation) at Rizhao on the Yellow Sea coast of northern China in April 1995, although this population was observed only in vivo and its identity awaits confirmation based on observations of silver-stained specimens ( Xu and Song 1999). In April 1998 we isolated it from the Japanese dosinia Dosinia japonica (Reeve) at Rongcheng on the Yellow Sea coast of northern China, where the prevalence was 11/20 and the intensity of infestation was light ( Xu and Song 2003).

Figures

Figs 14–25. Ancistrum acutum n. sp. from the surf clam Mactra veneriformis (14–17) and Ancistrum japonicum Uyemura, 1937 from the Japanese dosinia Dosinia japonica (18, 19, 21, 22) and the clam Cyclina sinensis (20, 23–25), from life (14, 15, 18–20) and after protargol (23–25) and silver nitrate impregnation (16, 17, 21, 22). 14 – left lateral view of a representative specimen; 15 – body variant and cortical granules; 16, 17 – ventral and dorsal view of the holotype specimen; 18, 19 – lateral view of living cells; 20 – lateral view of a representative specimen; 21, 22 – lateral view of same specimen; 23 – ventral ciliature; 24, 25 – lateral view of the neotype specimen. CCo – caudal complex; Cs – cytostome; CVP – contractile vacuole pore; M1–3 – membranelles 1–3; MA – macronucleus; MI – micronucleus; PM – paroral membrane; Sc – scutica; SK1, n – somatic kineties 1, n. Scale bars: 30 µm.