Pseudohaplocaulus
Pseudohaplocaulus Warren, 1988 (ref. ID; 2082)
[ref. ID; 2082]
Warren (1988) established the genus Pseudohaplocaulus "for Haplocaulus-like peritrichs which possess rows of regularly aligned pellicular tubercles and, therefore, reticulate silverline system". However, Warren (1988) did not prove whether the species he assigned to the new genus actually have a reticulate silverline system. Foissner et al. study shows that this is the case, and thus we recognize Pseudohaplocaulus as a distinct genus. Pseudohaplocaulus and Haplocaulus very likely differ only in this character like, e.g., Vorticella and Pseudovorticella. The evolutionary significance of the peculiarity is still to known. In spite of this, a generic distinction appears warranted because it structures the "difficult" peritrichs more clearly. (ref. ID; 2082)
- Pseudohaplocaulus anabaenae (Stiller, 1940) (ref. ID; 2082, 4613)
- Pseudohaplocaulus infravacuolatus Foissner & Brozek, 1996 (ref. ID; 2082 original paper, 4613)
- Pseudohaplocaulus nicoleae (Preche, 1935) (ref. ID; 2082)
Diagnosis
On average 60x40 um, campanulate. Macronucleus J-shaped in main body axis. 2 contractile vacuoles at ventral wall of vestibulum. On average 24 silverlines (mesh rows) between anterior end and aboral wreath and 20 silverlines between aboral ciliary wreath and scopula. Epiplanktonic. (ref. ID; 2082)
Descriptions
Slenderly to distinctly campanulate, about half of specimens nodding, i.e. more or less obliquely attached to main stalk axis. Stalk usually about as long as body, rarely up to 200 um, 4-6 um across, directly attached to cyanobacterial filaments or, possibly, also to their slimy sheath; equidistant, i.e. does not narrow distally; without conspicuous granules; does not or indistinctly contract helicoidally but sinuously, even in cells fixed for preparations; myoneme only slightly helicoidal, sometimes with inconspicuous thickening, extends to distal end of stalk; stalk sheath distinctly wrinkled during contraction. Contracted specimens barrel-shaped or clavate; cells not as contractile as most other vorticellids and thus often remaining partially extended when fixed for preparations; myoneme system, however, very similar to that of Vorticella, i.e. consisting of compact ring in peristomial collar and many thin strands extending between adoral ciliary spiral and scopula, forming rather distinct tube in posterior end continuing as stalk myoneme. Macronucleus invariably (n>20) in longitudinal axis of cell, J-shaped, both ends additionally often slightly curved, long anterior portion traverses peristomial disc, middle portion extends along ventral side; rarely specimens with almost rod-shaped nucleus. Micronucleus ellipsoid, near distal anterior end of macronucleus. Two contractile vacuoles, both invariably at ventral wall of vestibulum, one pre-equatorially slightly underneath vestibular opening, the other in body centre near cytostome. Pellicle with conspicuous tubercles, especially in anterior body half and on peristomial collar often studded with large blisters; lacking on peristomial disc; distinctiveness of tubercles varies in different specimens, but always recognizable at a magnification of > /_ x400, at least in anterior body half. Tubercles usually much more irregular than underlying pellicular alveoli as evident from peeled specimens and silverline system; contain granules and substance, both invisible in live specimens, staining with silver nitrate and protargol. Silver line meshes square to slightly hexagonal, frequently elongate in transverse axis of cell, especially underneath adoral ciliary wreath; distance of mesh rows rather constant between anterior end of cell and aboral ciliary wreath, distance of mesh rows rather constant between anterior end of cell and aboral ciliary wreath, gradually decreasing from ciliary wreath to scopula, as also evident from almost equal number of mesh rows. Silverlines associated with few to many granules, possibly pellicular pores, but no pores recognizable in SEM micrographs. Anlage of aboral ciliary wreath composed of closely spaced, oblique dikinetids in protargol slides; much more complicated after silver nitrate impregnation, i.e. consisting of 2-3 very closely spaced mesh rows framed by narrow somatic ones; whole complex thus composed of 4-5 very closely spaced silverline mesh rows with tubercles recognizable also in SEM micrographs. Scopula margin formed by tightly spaced granules; centre faintly to heavily impregnated in swarmers. Oral apparatus conspicuous, peristomial collar slightly to distinctly projecting, of usual thickness, contains a thick myoneme distally and some this myonemes proximally. Peristomial disc usually slightly convex, rarely flat, conspicuously protruding above peristomial collar in feeding specimens; not umbilicated. Vistibulum (infundibulum) in feeding cells almost transverse of many body axis and large as, e. g., in Vorticella convallaria. Oral infraciliature very much like in other votricellids. Cilia conspicuously long, viz. about 20 um, possibly due to the semiplanktonic mode of life, as supposed by Stiller (1940) in P. anabaenae. Haplokinety (undulating membrane) and polykinety (adoral ciliature) describe 1.5 turns (about 540 degrees) at peristomial disc before pluning down into vestibulum and accomplishing a further turn. Haplokinety possibly not accompanied by impregnable structure, commences 0.8-3.2 um (average 2.4, n=9) behind polykinety. Peniculus (adoral membrane) 1 twisted in vestibular portion, composed of 3 kineties (ciliary rows) usually terminating at same level, rarely (inner) kinety next to peniculus 3 slightly longer. Peniculus 2 terminates distinctly above peniculus 1, its right kinety invariably slightly shortened anteriorly and posteriorly. Peniculus 3 about 5-8 um long, posteriorly usually slightly projecting above peniculus 1, its inner kinety, next to peniculus 2, posteriorly shortened by about half of length and thus terminating at same level as peniculus 2; distance between inner and middle kinety slightly wider than between middle and outer kinety. Epistomial membrane, at least its 4-6 basal bodies, recognizable in both sessile specimens and swarmers, located at vestibular opening, i. e. far from distal end of adoral ciliary spiral. (ref. ID; 2082)
Swarmers: Swarmers observed only in stained preparations, disc-shaped with scopula in centre of aboral pole. Infraciliature as in sessile specimens, except for aboral ciliary wreath whose anlage develop to small kineties bearing long cilia. (ref. ID; 2082)
Comparison with related species
Warren (1988) founded Pseudohaplocaulus with two species, namely P. nicoleae (Precht, 1935), type of the genus, and P. anabaenae (Stiller, 1940). Pseudohaplocaulus nicoleae is an epizoite of a marine polychaete, Nicolea zostericola, and has only a single, ventral contractile vacuole. Thus, it cannot be confused with P. infravacuolatus. At first glance, our species closely resembles P. anabaenae (Stiller, 1940) Warren, 1988, especially in having two contractile vacuoles and a similar size shape, pellicular structure and habitat. However, the location of the contractile vacuoles is different: both are situated at the ventral wall of the vestibulum in P. infravacuolatus, whereas one vacuole is located at the dorsal vestibular wall in P. anabaenae. Stiller (1940) described "The animal has two contractile vacuoles; one at the dorsal pharyngeal wall at the level of the peristomial collar, the other deep in the body near the end of the pharynx". We consider this difference sufficient to separate our population from P. anabaenae because the number and location of the contractile vacuoles is a very constant character and is used by many authors to distinguish species in peritrich and other ciliates. Furthermore, Canter et al. (1992) depict a peritrich from Anabaena lemmermannii, very like a Pseudohaplocaulus, which has the contractile vacuoles located exactly as described Stiller (1940). In addition, Canter's species apparently has a small vestibulum as mentioned by Stiller (1940) in P. anabaenea. There are some other character which differ in P. infravacuolatus and P. anabaenae, namely the size (length 47-67 vs. 40-45 um), the vestibulum (unusually small in P. anabaenae), the equidistant stalk (gradually narrowed in P. anabaenae), and the pellicular structure (tubercles of same size and distinctiveness throughout in P. anabaenae). These characters are not as crucial as the contractile vacuoles but should not be neglected because Stiller's description is rather detailed and based on abundant material found in Lake Plon, Germany.
Pseudohaplocaulus infravacuolatus cannot be reliably distinguished from Pseudovorticella chlamydophora and P. monilata using the number of silverline mesh rows as diagnostic character. Both of course differ by the stalk, which contracts helicoidally, from Pseudohaplocaulus, whose stalk contracts in zigzag. Pseudovorticella chlamydophora differs from P. infravacuolatus also by its single contractile vacuole. Pseudovorticella monilata is very similar in all characters, even in the number and location of the contractile vacuoles. All distinguishing characters of these three species are recognizable only in live specimens. Live observation is thus essential for their correct identification. (ref. ID; 2082)
Comparison with literature data
There are several records and micrographs in the ecological literature showing peritrichs attached to planktonic cyanobacteria. Unfortunately, the morphological data contained in these papers are too incomplete for a definite a posteriori identification. However, all very likely belong either to P. anabaenae (Stiller, 1940), or P. infravacuolatus. Kerr (1983) depicted a Vorticella prevailing on planktonic colonies of Nostoc sp. (Anabaena sp. according to Canter et al. 1992) in Balsam Lake, USA. Its habitat, size (length about 40-50 um according to the figures), shape, and short, weakly coiled stalk (up to length of body according figures) suggest that it belongs to Pseudohaplocaulus; possibly it was P. anabaenae because, with some imagination, one can recognize two contractile vacuoles in the position typical for this species in Figure 4 of Kerr's paper. Pratt and Rosen (1983) found a peritrich ciliate associated with Anabaena flos-aquae in Lake Douglas, USA. They identified it as Vorticella monilata (now Pseudovorticella, Warren, 1988) and provided two figures but, unfortunately, no description. Pseudovorticella monilata and Pseudohaplocaulus infravacuolatus are indeed similar in many characters and thus Pratt and Rosen's identification cannot be entirely refused. However, their Figure 1, which shows many contracted specimens, suggests that it was a Pseudohaplocaulus because the stalks are short and uncoiled, unlike in Pseudovorticella monilata, which usually has a long stalk distinctly coiled in contracted specimens. Canter et al. (1990, 1992) provided a lot of beautiful micrographs from a peritrich attached in great numbers to planktonic colonies of Anabaena lemmermanni occurring in Lake Windermere, England. Like Pratt and Rosen (1983), they identified it as Pseudovorticella monilata, with the help of B.J. Finlay. Again, we suggest that this was a Pseudohaplocaulus because of the short stalk which obviously contracted in zigzag and not spirally as in Pseudovorticella (see Fig.5 in Carter et al. 1992; Fig.10 shows a dead specimen with a helicoidally contracted stalk sheath, whereas the stalk myoneme is uncoiled indicating that this species cannot contract the stalk helicoidally). Furthermore, Figure 5 in Canter et al. (1992) strongly suggests that it was P. anabaenae because the contractile vacuoles are exactly in the position described for this species. (ref. ID; 2082)
Etymology
infra (below) because both contractile vacuoles are below (at the ventral wall) of the vestibulum, as opposed to P. anabaenae, which has one of its two vacuoles above the vestibulum, i.e. at the dorsal wall. (ref. ID; 2082)
Type specimens
Two holotypes and two syntypes of P. infravacuolatus as four slides of protargol- (Wilbert technique) and sliver nitrate- (Klein-Foissner technique) impregnated cells, respectively, have been deposited in the collection of microscopic slides of the Oberosterreichische Landesmuseum in Linz (LI), Austria. (ref. ID; 2082)
Measurements
Body length (in vivo) 60.0 (47-67); body width (in vivo) 40 (32-42) um. Silverlines from anterior end to aboral ciliary wreath (extremes 21-26, mean 24); silverlines from aboral ciliary wreath to scopula (extremes 16-22, mean 20); silverlines ratio 0.83 (ref. ID; 2082)