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The World of Protozoa, Rotifera, Nematoda and Oligochaeta

Platyophryides

Platyophryides Foissner, 1987 (ref. ID; 4409)

[ref. ID; 4409]
Platyophryides differ from Platyophrya in that the adoral membranelles are parallel to the paroral in the former genus and perpendicular to it in the latter. Foissner (1992) distinguishes three species in the genus, differing essentially on morphometric characteristics: Platyophryides latus (Kahl, 1930) Foissner, 1987 (65-120 um long, 28-37 somatic kineties, and 5-8 adoral membranelles); Platyophryides dragescoi Foissner, 1987 (70-100 um long, 19-22 somatic kineties, and 3-4 adoral membranelles); and Platyophryides magnus Foissner, 1992 (more than 130 um long, 40-55 somatic kineties, and 9-10 adoral membranelles). Foissner suspects that the three species could be variations of the same form, which our observations support. (ref. ID; 4409)
  1. Platyophryides dragescoi Foissner, 1987 (ref. ID; 4409)
  2. Platyophryides latus (Kahl, 1930) Foissner, 1987 (ref. ID; 4409)
  3. Platyophryides magnus Foissner, 1992 (ref. ID; 4409)

Platyophryides latus (Kahl, 1930) Foissner, 1987 (ref. ID; 4409)

Descriptions

When fed on bacteria and maintained in a culture medium made from a wheat infusion and yeast extract, the Protargol-stained ciliates are ovoid, about 85 um in length (60-110 um, n=32) and 68 um in width (50-90 um, n=32). The somatic kineties, composed of dikinetids, are slightly spiralled, numbering 42 (34-48, n=23), with two to three more right kineties (16-25) than left kineties (15-22). There are no pre- or post-oral sutures and no pseudomembrane formed from the ends of the left somatic kineties. The median macronucleus is ovoid, 17-22 um in length, and is flanked by a small micronucleus. There is a posterior contractile vacuole. The subapical buccal region is elongated along the anterior third of the ventral surface. From 30-45 um (n=23) in length, it is bordered on its right by a paroral formed from a double row of kinetosomes and five to nine (n=23) adoral membranelles. The anterior and posterior ends of the paroral curve toward the left a either end of the superficial buccal region. The adoral membranelles are aligned almost parallel to the long axis of the buccal region along its left side. When these cells have fed, they become immobile after rotating in one place. They secrete a cyst and undergo one or two divisions. Under unfavorable conditions, resting cysts with three wall layers appear. When the cell density is high or when Tetrahymena or, even more effectively, Colpidium are introduced, active predatory giant forms appear. Their size is quite variable, up to 5 times the size of the bacterivorous forms. The number of somatic kineties more than doubles (87-112; n=19), while the small difference between right kineties (46-58) and left kineties (41-54) is maintained. The buccal region increases to 180-220 um (n=8) in length, with the paroral maintaining its position along the right side of the buccal region and the number of adoral membranelles increasing to 15-20 (n=8). The macronucleus remains ovoide but increases to 50-78 um (n=13) in length. If regularly fed ciliate prey, these giant forms grow and divide within cysts, like the bacterivorous forms. However, if the prey numbers decrease, the cells rapidly become small. In addition to division within cysts, resting cysts of the giant forms have also been observed. (ref. ID; 4409)
  • Ultrastructure: The alveolar layer is usually very flattened and the epiplasm is very thin. Dikinetids are implanted in cortical grooves and accompanied by three parasomal sacs. The two kinetosomes of each dikinetid are ciliated and united by three desmoses. Two lateral desmoses link triplets 9 and 1-2 of the anterior kinetosome to triplets 5-7 and 3-4 of the posterior kinetosome, respectively, while the median desmose links triplets 5-6 to triplets 9-1. The anterior kinetosome bears the following: 1) two to four postciliary microtubules, which are not always visible; 2) a tangential ribbon of about 15 transverse microtubules, at first obliquely directed before becoming transverse to the kinety and extending into the adjacent ridge; and 3) a dense material associated with the transverse ribbon. The posterior kinetosome bears the following: 1) a postciliary ribbon of four to six microtubules; 2) a short, thick kinetodesmal fibril; 3) a transverse ribbon of about a dozen microtubules, directed towards the rear and overlapping the ribbons of more anterior kinetosomes; and 4) a short dense fiber. In some sections, a massive fiber with periodic striations is linked to triplets 3-4 of the posterior kinetosome. Mucocysts are numerous and the macronucleus and micronucleus have their own distinct nuclear envelopes. The paroral is composed of two rows of kinetosomes: an internal row of non-ciliated kinetosomes, bearing postciliary ribbons and possibly transverse ribbons; and an external row of ciliate kinetosomes, bearing postciliary ribbons and giving rise to oral nematodesmata. Each adoral membranelle seems to be composed of groups of three ciliated kinetosomes: two kinetosomes (KS1, KS2) are joined to each other and the more external one gives rise to a nematodesma; and the third kinetosome (KS3) is adjacent to KS2 and also gives rise to a nematodesma. The cytopharynx is limited on its inside by ribbons of microtubules that extend toward the posterior, forming a simple circular layer and, on its outside, by the nematodesmata originating from the paroral and adoral membranelles. Phagoplasm is conspicuous under the buccal surface. (ref. ID; 4409)