Balanion
Balanion Wulff, 1919 (ref. ID; 7477)
Order Prostomatida (ref. ID; 7040)
Order Prorodontida Corliss, 1974: Family Balanionidae Small & Lynn, 1985 (ref. ID; 7477)
[ref. ID; 7477]
The genus is typically barrel-shaped with a flattened anterior oral region, which is encircled by dikinetids. Oral flaps also encircle the oral region in B. comatum and B. planctonicum. Within the circle of oral dikinetids is a group of oral cilia, "the brush" or "brosse", arising from a few specialised short kineties or kinetal segments (Bardele, 1999, Lynn et al., 1999); in Balanion the brush may be reduced to only a few kinetosomes, which may be impossible to see without the aid of electron microscopy and even then may be difficult to recognize (Bardele, 1999). Thus, for routine ecological studies, the brush is not a useful diagnostic feature; observation of the its variation will likely be restricted to phylogenetic studies. The cell body is surrounded by several, equally spaced, longitudinally-oriented somatic kineties composed of monokinetids, extending only part way down the cell. The posterior of the cell is bare, and typically possesses a single caudal cilium, located in a small dipression. Lynn and Small (1999) distinguished the Family Balanionidae by the placement of the brush within the circle of oral dikinetids; this distiction is supported by Bardele (1999). (ref. ID; 7477)
- Balanion comatum Wulff, 1919 (ref. ID; 1619, 3540, 7477 redescribed paper)
- Balanion planctonicum (Foissner, Oleksiv & Muller, 1990) (ref. ID; 4611, 4613) reported author and year? (ref. ID; 1629, 7040, 7141, 7477)
Syn; Pseudobalanion planctonicum Foissner, Oleksiv & Muller, 1990 (ref. ID; 4611, 4613)
Balanion comatum Wulff, 1919 (ref. ID; 1619, 3540, 7477 redescribed paper)
Descriptions
The cell is cylindrical with a flattened anterior end and rounded or bluntly-pointed posterior end. Live cells are transparent, when viewed with light microscopy, except when they have ingested pigmented food, at which times their food vacuoles acquired the colour of their prey. A distinct "lip" exists around the anterior end; in protargol-stained cells the lip may be underlain by dark material. In preserved material, the flattened anterior end (the oral disk) often forms a dome with the perimeter recessed in a groove, internal to the circumoral lip. The closely packed "bulbs", which occur at the base of the oral flaps, may form the lip. The cytostome is rarely observed in protargol-stained, Lugol's iodine preserved, TEM, or live specimens, but a slight funnel-like central depression occurs occasionally. The cell is 15 um (range, 10-24) long and 10 um (7-13) wide. Twenty five (20-29) somatic kineties extend 75% (50-90) of the cell length. The posterior end of the cell is bare, except for a single caudal cilium (total length 10-15 um) that arises from a small central depression; the posterior portion of the caudal cilium (3-4 um) is tapered and was not visible in our protargol-stained cells. Somatic kineties possess 18(12-26) monokinetids. Somatic cilia extend perpendicular to the cell length and typically curve anteriorly; length 5-8 um. The anterior end of the cell is completely surrounded by a circle of 40 (35-46) ciliated dikinetids. The oral cilia are directed anteriorly; length 8-11 um. An oral flap originates at the base of each oral dikinetid, internal to the dikinetid. In preserved material there is a swollen "bulb" at the base of each flap (~0.5 um wide). Each oral flap possesses 9-10 supportive microtubules (visible in TEM preparation only), running the length of the flap. The oral flaps extend anteriorly; length 5-10 um. Fine filaments may extend for 5-7 um beyond the end of the flaps; these are likely ejected extrusomes. A reduced number (>/_ 2, exact number unknown at this time) of brush kinetosomes occur within the circle of oral kinetids. The brush kinetosomes prossess clavate ciliary stumps that are difficult to observe in TEM sections and are not recognisable in protargol-stained, live, or Lugol's preserved specimens. One spherical macronucleus is positioned slightly anteriorly and acentrically; diameter 4 um (3-7). (ref. ID; 7477)
Swimming behavior: The swimming behavior of B. comatum is typical of many marine planktonic ciliates and can be divided into two patterns: swimming in a helix and occasional tumbles, followed by a fast jump. The swimming helix had a diameter of 50 to 100 um and a mean frequency of ~1 sec-1. The swimming speed along the helical path was ~450 um sec-1, and the mean linear displacement of one turn of the helix was ~400 um, although cells did swim in a circle or in almost a straight line at times. Jumps appeared to be initiated both spontaneously and by contact with objects and were at rates of up to 3,000 um sec-1, travelling distances that were at times >1,000 um. When prey cells were captured, they appeared to stick to either the oral cilia or the flaps. After a R. salina cell was captured, the ciliate darted back and forth, about one cell length, 3-5 times. It may be that, as the oral disk of the ciliate (~8.7 um) is smaller than the length of the prey (12 um long by 7 um wide), the ciliate must orient the prey in order to ingest it. After the prey was engulfed the ciliate resumed its swimming in an helix. Prey capture and handling took no more than 5 sec. Length and width of Lugol's fixed cells were affected by food concentrations under which the cells are cultured. However, the length:width ratio (1.43+/-0.08, SD) and the oral disc diameter (8.65+/-0.45 um) of Lugols' fixed specimens were independent of food concentration. Thus, these two characters may be useful to distinguish Balanion comatum from other species, regardless of ambient prey concentrations. (ref. ID; 7477)
Comparison with related species
Lynn and Small (1999) used an undescribed species of illustrate the genus Balanion in a recent guide to the ciliates: the illustration they provide is distinctly different from the two described species of Balanion: B. comatum Wulff, 1919 and B. planctonicum (Foissner et al.) Foissner et al., 1994. However, the two described species are remarkably similar. The mean values of a number of characters differ between the ciliate we describe above and Balanion planctonicum, which is a freshwater species, but there is considerable overlap in the range of most characters. Besides the difference in habitats, there are two clear characters that separate these species: the number of kinetosomes in the somatic kineties and the number of supportive microtubules in the oral flaps. These features are difficult to observe but adequately distinguish the two species. Structures, of particular interest in the comparison of the two species of Balanion are: 1) the circumoral microtubular ribbons ; 2) the oral dikinetid-flap complex; and 3) the brush. Many prostomatids possess a band of circumoral microtubules (comt) forming a ribbon associated with the oral dikinetids, and Balanion is no exception. The "comt" is easily observed in TEM preparations and may be the darkly staining structure at the base of the oral cilia, in protargol-stained specimens. Bardele (1999) speculated that the "comt" may be either contractile, aiding in ingestion, or supportive, forming a rigid structure. Our data indicate that the oral disk diameter remains constant, regardless of the ciliate's nutritional state. Furthermore, the oral disk diameter remains slightly larger (8.7 um) than the optimal prey size (7x12 um) of B. comatum. We therefore speculate that the "comt" is a non-contractile structure. In contrast, W. Foissner (pers. commum.) has observed that the anterior of Balanion planctonicum is highly flexible during prey ingestion; this has also been illustrated. Clearly, the function of this structure requires further elucidation. The oral dikinetid-flap complex, which may appear in light microscopy to be a fused structure, formed by oral cilia, is clearly composed, in both species of Balanion, of two separate cilia and a flap. Furthermore, in both Balanion species the base of the flap swells to form a "bulb", which may be caused by swelled pellicular alveoli, although its exact architecture is unknown (Bardele, 1999). Furthermore, like B. planctonicum, B. comatum appears to possess extrusomes in the flaps, and these are likely toxicysts (Bardele, 1999). The brush kinetosomes in both Balanion species are highly reduced and are only visible in TEM sections (Bardele, 1999) or in deciliated SEM preparations. Balanion planctonium has two sites on the oral disk where single cilia emerge from an oral disk dikinetid. We have only observed a single pair of clavate ciliary stumps within the circle of oral dikinetids; there may be other pairs, but they were not observed in serial TEM sections of the oral region. Furthermore, B. comatum was not easily deciliated, following the method of Bardele (1999), and we were unable to use this method to determine the exact number of brush kinetosomes. Balanion comatum was originally observed in a similar habitat to our isolate, but the description of the original isolate differs from ours in several minor ways. Most of these differences can be accounted for by the quality of observational and preservational techniques at the turn of the 20th century, but the most remarkable difference is that the original description has a pronounced oral depression, which Wulff (1919) emphasised. In contrast, this feature was rarely observed in our isolate. As the presence of an oral depression may virtually disappear (related to feeding) in Balanion planctonicum, we have considered it to be a diagnostic feature. The other features that might be used to differentiate these two isolates either overlap in range, may vary depending on nutritional state, preservation of material, and staining techniques, or are not included in the original description of B. comatum. Therefore, we have been conservative and consider our species of represent an isolate of B. comatum. Our data comprise the first redescription of this species. (ref. ID; 7477)
Locality of isolation
Denmark, Oresund, the straight separation the Kattegat and the Baltic (buoy M4; 56 degrees 03'30N, 12 degrees 39'00E) at a depth of 5-10 m, temperature of 10-12 degrees C, and salinity of 22-26 0/00. (ref. ID; 7477)
Deposition of type material
A slide of protargol-stained cells representing a neotype resides in the collections of the Natural History Museum, London, UK, with registration number 1999:1:11:1. (ref. ID; 7477)
Balanion planctonicum (Foissner, Oleksiv & Muller, 1990) (ref. ID; 4611, 4613) reported author and year? (ref. ID; 1629, 7040, 7141, 7477)
Synonym
Pseudobalanion planctonicum Foissner, Oleksiv & Muller, 1990 (ref. ID; 4611, 4613)
Descriptions
Algivorous ciliates. (ref. ID; 7141)