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Protistology 1, 30-33 (1999) April, 1999
Protistology
Korotnevella diskophora n.sp. (Gymnamoebia, Paramoebidae) - small freshwater amoeba with peculiar scales
Alexey V. Smirnov
Department of Invertebrate Zoology, Faculty of Biology and Soil Sci, StPetersburg State University
Summary
A new freshwater amoeba species, Korotnevella diskophora, is described. This species is the smallest representative of the genus; it had most probably been already noted by researchers (as an unidentified isolate) due to its peculiar, disk-shaped scales. All known freshwater scale-bearing amoebae differ in the scale structure, while marine species have similar scales.
Key words: amoebae, Lobosea, Gymnamoebia, morphology, systematics, scales
Introduction
The genus Korotnevella (Schaeffer, 1926) Goodkov, 1988, formerly known as “Dactylamoeba Korotneff, 1880” (Page, 1982; 1988; 1991) and renamed in 1988 (Goodkov, 1988; Smirnov, 1996), includes scale-bearing gymnamoebae without a parasome. Two freshwater and one marine species are known within this genus (Page, 1991; Smirnov, 1996), and it is highly probable that more species exist and even had been observed by researchers (Bovee, 1953; Pennick & Goodfellow, 1975; Page, 1983), but remain undescribed or had not been studied electron-microscopically. It was noted (Smirnov, 1996) that in two known marine species of scale-bearing amoebae (Korotnevella nivo and Paramoeba eilhardi), the structure of scales is similar, while the two known freshwater species (Korotnevella stella and K.. bulla) have different scales. One more freshwater species reported here also have a peculiar scale structure.
Samples of the bottom sediments containing amoebae were collected from freshwater lake Leshevoe (Valamo Island, the Lake Ladoga, North-Western Russia) at a depth of 0.5 m. Amoebae were cloned and supported on NN agar (Page, 1988), with the overlay of PJ (Prescott & James, 1955) mineral medium. For EM study amoebae were fixed using three different fixation procedures, described earlier in detail (Smirnov & Goodkov, 1997).
Results and discussion
The amoeba is of dactylopodial morphotype (definition in: Smirnov & Goodkov, 1999) and in locomotion (Figs. 1) frequently resembles an irregular triangle with the basis situated anteriorly. A moving cell usually has a wide anterior hyaline zone, from which it produces a finger-shaped subpseudopodia (dactylopodia) (Figs. 1-2). Sometimes, the moving cell elongates in antero-posterior direction and forms one or two long, thin, anteriorly directed subpseudopodia (Fig. 3). However, cells of this sort do not seem to be pre-floating, and are able to keep this type of organisation and to move with these pseudopodia for a long time. Some specimens have bulbous uroid (Fig. 1), but most lack differentiated uroidal structures (Fig. 4). The average length of the locomotive form is 23 ^m (1634 ^m), breadth, 9 ^m (6-14 ^m); L/B 2-2.5.
When not moving, the amoebae are rounded, sometimes with small dactylopodia. The floating form has 1-4 very long, thin, tapering hyaline pseudopodia (Fig. 9). The cell has one vesicular nucleus 1-2 ^m in diameter, with rounded central endosome (Fig. 8). One contractile vacuole is present. There is no cytoplasmic cristals. Cyst were not found in our cultures.
Electron microscopy show that the amoeba is covered with disk-shaped scales (Figs. 5-7). Each scale has conical projection in the middle, resembling a specific sort
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of hat (Fig. 7). The diameter of the scale is about 350 nm, and the central projection is about 80 nm high. Cytoplasmic organelles were never well preserved. Based on the material available, we can only state that the cell has mitochondria with dense matrix and tubular, probably anastomosing cristae (Fig. 6). The nucleus has a dense, nearly compact central nucleolus and numerous patches of electron-dense material (probably chromatin), situated throughout between the nucleolus and nuclear envelope (Fig. 8). A single large dyctiosome is situated near the
nucleus. This species seems to be bacteriofagous, with single bacteria enclosed in the phagosomes visible in the cytoplasm (Fig. 5).
This species undoubtedly belongs to the class Lobosea, subclass Gymnamoebia, family Paramoebidae, genus Korotnevella (due to the morphotype, pseudopodial pattern, and the presence of scales) and obviously represents a new species, because of the small size and peculiar shape of its scales. We named it Korotnevella discophora, according to the disk-like basis of its scales.
Fig. 1-8.
1-4: Different locomotive forms of Korotnevella discophora. 5: Overwiev ofthe cell covered with scales (arrowed). 6: Mitochondria and scales (arrowed). 7: Scales (arrowed) under higher magnification. 8: Nucleus. Scale bar is 5 pm for 1-4 and 0.5 pm for 5-8.
32 ■ Alexey V. Smirnov
Diagnosis
Class Lobosea Carpenter, 1861
Subclass Gymnamoebia Haeckel, 1862
Family Paramoebidae (Poche, 1913) Page, 1987
Genus Korotnevella (Schaeffer, 1926) Goodkov, 1988
Korotnevella diskophora n. sp.
Irregularly triangular or elongate in locomotion, usually with several short dactylopodia, but sometimes with 1-2 very long, thin, tapering hyaline pseudopodia. Bulbous uroid may be present. Average length of the locomotive form, 23 ^m (16-34 ^m); breadth, 9 ^m (6-14 ^m); L/B 2-2.5. Floating form irregular, with 1-4 very long, thin, tapering pseudopodia. One vesicular nucleus, 1-2 ^m in diameter, with compact central endosome and patches of dense material throughout the caryoplasm. Cyst unknown. Cell covered with disk-shaped scales; each scale has conical projection in the middle, resembling a specific sort of hat. Diameter of the scales about 350 nm, and height of central projection, about 80 nm. Bacteriophagous, freshwater.
Type location: bottom sediments of the lake Leshevoe (Valamo Archipelago, the Lake Ladoga, North-Western Russia), from a depth of 0.5 m.
Type material: Holotype No 919; paratype No 920. Type slides are deposited with the collection of preparations of the Biological Research Institute, St. Petersburg State University.
Differential diagnosis the present species is smaller than both other known freshwater species of Korotnevella and has a peculiar floating form, which does not resemble those of K. bulla andK. stella. It can well be distinguished from any known species with the use of EM, due to its peculiar scales.
It is interesting to note that the present species most probably represents “Mayorella sp. 3”, noted by Pennick and Goodfellow (1975). These authors presented EM of the surface of this isolate, having the same characteristic scales. However, this EM picture was the only data on this isolate in their paper.
Smirnov (1996) noted that all three studied isolates of marine Korotnevella (including the only named species, K. nivo) (Grell & Benwitz, 1970; Anderson, 1977; Smirnov, 1996) have similar scales, resembling that of P. eilhardi. In contrast, both previously known freshwater species of Korotnevella have different, peculiar scale pattern. The present isolate resembles none of known species, and adds one more pattern of the scale organisation among Gymnamoebia. However, all members of the genus Korotnevella belong to the same morphotype and have similar ultrastructure (excuding the scale structure).
Sometimes, the form of Korotnevella discophora trophozoites (see Fig.3) resembles the amoebae described by Bovee (1953, 1953a, 1970) as members of the genera Oscillosignum, Subulamoeba and Flagellipodium. Members of these genera were not studied with EM, and their systematic position is unclear. However, they may be po-
Fig. 9 - floating forms of Korotnevella discophora, scale bar is 5 pm
tential candidates for inclusion into the genus Korotnevella in its current status, provided they are reliably re-isolated and studied.
Acknowledgements
The work was supported with the RBFR grant 98-0449815, provided to A.V. Goodkov, and a grant from St. Petersburg Committee on Culture and Higher Education, provided to A.V. Smirnov. This work was based on the material collected over many years at the field station of the Valamo Expedition of St.Petersburg Soc. of Naturalists.
References
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Address for correspondence: A.V. Smirnov, Dept. of Invertebrate Zoology, Fac. of Biology & Soil Sci., St.Petersburg State University, 199034, Universitetskaja nab. 7/9, St.Petersburg, Russia. E-mail: smirnov@as2187.spb.edu
The manuscript is presented by A.V.Goodkov
