Hemigastrostyla szaboi, Wilbert & Song, 2005

Wilbert, Norbert & Song, Weibo, 2005, New contributions to the marine benthic ciliates from the Antarctic area, including description of seven new species (Protozoa, Ciliophora), Journal of Natural History 39 (13), pp. 935-973 : 966-969

Hemigastrostyla szaboi nov. spec.

( Figure 11A–D , 16G–L ; Table VIII)

Diagnosis Medium-sized marine Hemigastrostyla in vivo about 100–150630–50 M m with elongated

body shape; ca 27 adoral membranelles, eight (including one buccal) frontal, five ventral, five transverse and three caudal cirri; left and right marginal row each with 23 cirri on average, three dorsal kineties; two macro- and two to six micronuclei.

Dedication

We dedicate this species to the Hungarian protozoologist, Dr Andras Szabo, in recognition of his contributions to the study of ciliates.

Description

Cells generally inflexible; body shape distinctly slender with both ends only slightly narrowed, ratio of cell length to width about 3:1 ( Figure 11A ); buccal field narrow, about one-third to two-fifths of body length; dorsoventrally flattened 1:2. Cell margins generally parallel but in anterior portion often slightly swelling outward. Ventral side conspicuously grooved because of the presence of marginal rows ( Figure 11A , arrow).

Pellicle thin; no cortical granules recognizable (not carefully observed). Cytoplasm often containing numerous light-reflecting globules (3 M m across), which render the cell completely dark, especially in posterior portion of body. Food vacuoles basically not detectable. No contractile vacuole detected. Two macronuclei, elongate and often conspicuously separated from each other ( Figures 11D , 16K ); two to five oval micronuclei near macronuclei ( Figure 16G , arrows).

Movement relatively slow, crawling without pause on debris.

Buccal field narrow, adoral zone of membranelles (AZM) extending to about one-third of body length, bases of membranelles up to 8 M m long, cilia ca 15 M m long in vivo. Distal end of adoral zone of membranelles bending considerably posteriad at right margin. Paroral and endoral membranes about equally long, parallel to each other. Pharyngeal fibres short and conspicuous after protargol impregnation ( Figure 11C ).

Frontal area constantly eight cirri, anterior two to three of which are distinctly enlarged, while others are smaller ( Figure 11C ). Single buccal cirrus (counted among frontal cirri in Table VIII), situated beside mid-point of undulating membranes. Three postoral ventral cirri anteriorly located, immediately beneath the cytostome level ( Figure 11C ), while two pretransverse ventral cirri close to five terminally positioned thick transverse cirri. Right marginal row terminating subcaudally anterior to rightmost transverse cirrus, which often gives an appearance of confluence of right marginal cirri and TC ( Figure 16L , arrow). Cirri in both marginal rows rather large and densely spaced; anterior portions of right marginal row often extending on to dorsal side. At posterior end, the two marginal rows widely separated. All cirri associated with strongly impregnated fibre system ( Figures 11B , 16I, L ).

Dorsal kineties constantly three, cilia about 3 M m long, positioned in small pit as recognized after impregnation. Three caudal cirri located caudally on cell margin ( Figure 11D , arrowheads).

Remarks

The genus Hemigastrostyla previously contained only two species ( Borror 1963; Song and Wilbert). This new organism can be separated from the closely related H. enigmatica (Dragesco and Dragesco-Kernéis 1986) Song and Wilbert by having fewer frontal and buccal cirri (eight versus consistently more than eight in the latter), no ‘‘extra’’ ventral cirri (versus present), fewer dorsal kineties (three versus five) and the body shape (non-cephalized versus cephalized) (Dragesco and Dragesco-Kernéis 1986; Song and Wilbert 1997). Differences from H. stenocephala ( Borror 1963) Song and Wilbert 1997 , are that the new species has conspicuously shorter dorsal cilia (ca 3 versus 16 M m in length in H. stenocephala ), fewer frontal and ventral cirri (13 versus 17), less slender body shape and no extra ventral cirri (versus two in H. stenocephala ) ( Borror 1963).

Figures

Figure 11. (A–D) Hemigastrostyla szaboi nov. spec. and (E–K) Amphisiella antarctica nov. spec. from life (A, E–H) and after protargol impregnation (B–D, I–K). (A) A typical specimen, arrow marks the groove, where the marginal cirri are positioned; (B) posterior portion of ventral side, arrow marks the two small ventral cirri, doublearrowheads indicate the transverse cirri, arrowhead points to the posterior end of right marginal row, note that there is a conspicuous gap between the transverse and right marginal cirri; (C) ventral view, arrow marks the undulating membranes, while the arrowhead indicates the position where the right marginal row and transverse cirri join together; (D) dorsal view, arrow indicates the anterior end of right marginal row, while arrowheads mark the caudal cirri; (E) ventral view of a typical individual; (F) dorsal view, to show the cortical granules; (G) lateral view, to demonstrate the flattened body shape; (H) to show the flexible body; (I) anterior portion of ventral side, arrowhead indicates the double-rowed paroral membrane, arrow marks the endoral membrane; (J) ventral view, arrowheads mark the extrusomes, which are positioned along undulating membranes, arrow indicates the posterior end of ventral row, while double-arrowheads mark the transverse cirri; (K) dorsal view, arrows mark the micronuclei, double-arrowhead indicates the caudal cirri. Scale bars: 50 Mm (A, C); 80 Mm (E); 30 Mm (I); 60 Mm (J, K).

Figure 16. Photomicrographs of (A–F) Amphisiella antarctica nov. spec. and (G–L) Hemigastrostyla szaboi nov. spec. after protargol impregnation. (A) Ventral view of buccal region, to show the ventral row (arrow); (B) macro- and micronuclei (arrows); (C, E) buccal area, to show the argentophilic granules along the undulating membranes (arrows and arrowheads); (D) caudal portion, to show the transverse and caudal cirri; (F) ventral view, arrow marks the micronucleus; (G) nuclear apparatus, arrows indicate the micronuclei; (H) to show the fibres associated with the marginal cirri; (I) ventral view of posterior cell end, to show the transverse cirri, note that there is no gap between right marginal row and the transverse cirri; (J) ventral view, to show the general appearance of infraciliature; (K) ventral view, to show a slender form, arrow indicates the distal end of adoral zone of membranelles; (L) ventral view of caudal region, arrow marks the transverse cirri.