Korotnevella
Korotnevella (Page, 1981) Goodkov, 1988 (ref. ID; 4891)
Class Flabellinea: Order Dactylopodida (ref. ID; 6789)
- Korotnevella bulla (ref. ID; 4891)
- Korotnevella nivo Smirnov, 1996/97 (ref. ID; 4891 original paper)
- Korotnevella stella (ref. ID; 4891, 6789)
Descriptions
Freshwater species. (ref. ID; 4891)
Korotnevella nivo Smirnov, 1996/97 (ref. ID; 4891 original paper)
Diagnosis
Body triangular or elongate during locomotion. Subpseudopodia hyaline, short finger-shaped or long conical (up to 1.5 times body length). Mean length of the locomotive form 39 um (19-51 um), mean breadth 21 um (14-40 um). Mean length/breadth ratio (L/B) 1.9 ranging between 0.95 and 2.8. Nuclear diameter 2.2-3.8 um in live specimens and 3.4-4.5 um in stained preparations. Capable of living and multiplying in seawater (35 0/00) and does not survive in freshwater. Length of each scale 400-514 nm, breadth 170-230 nm and width about 200 nm. (ref. ID; 4891)
Differential diagnosis
Korotnevella nivo differs well from both freshwater species of this genus by the tendency to produce very long anterior hyaline pseudopodia. It does not survive in freshwater. It has a nucleus with a distinct structure with differs from that of may freshwater scale-bearing species. At the light-microscopic level it may be confused with some marine Vexillifera, but the structure of the cell coat allows it to be differentiated from the members of this genus. (ref. ID; 4891)
Descriptions
During locomotion the amoebae had a variable shape; usually they were elongate or more or less triangular. They produced only hyaline subpseudopodia which were short and finger-shaped or long (up to 1.5 times the body length) and conical. The latter type is very characteristic for this species. The cell could sometimes be broad and triangular, with 3-5 anteriorly directed, long pseudopodia. In this case it resembled some marine members of the genus Vexillifera (Page 1983). The locomotive form without long pseudopodia resembled that of Neoparamoeba pemaquidensis (Page 1970, 1983; as Paramoeba) or the limnic Korotnevella stella. The frontal hyaloplasm always formed the border which had a variable width and which was more flattened than the granuloplasmic region of the body. The pseudopodia often continued as ridges on the dorsal surface of the amoeba and three or four of these ridges were usually present in the locomotive form. In most cases there was no differentiated uroid, but sometimes the posterior end of the amoeba was plicate or irregularly morulate. During continuous locomotion the amoebae always lacked differentiated uroidal structures. The subpseudopodia never determined the direction of the locomotion. In order to change the direction of movement the amoeba formed a broad wave of hyaloplasm which was thrown out in the current direction of movement. When resting the amoeba had an irregular shape or rounded with many short, hyaline finger-shaped projections. These projections were formed in all directions from both the lateral and the dorsal hyaloplasm. The floating form was radial and it had from three or fifteen long, tapering and pointed hyaline pseudopodia. The longest were 3-4 times the diameter of the central mass of cytoplasm. The nucleus was vesicular with a single nucleolus which was located centrally or slightly eccentrically. The nucleolus was visible in both living specimens and in haematoxylin-stained preparations. The diameter of the nucleus, measured in living specimens, was 2.2-3.8 um, that of the nucleolus was 1.2-2.2 um. In stained preparations the nucleus was 3.4-4.5 um in diameter. A parasome was not detected, neither in living specimens nor in stained preparations. Feulgen-stained preparations showed a slightly Feulgen-positive nucleus with a small central or eccentric Feulgen-negative lacuna and no evidence of a parasome. DAPI staining showed a homogeneously fluorescent nucleus without discernible internal differentiation and no evidence of other fluorescent inclusions, except for the food vacuoles in some specimens. No contractile vacuole was observed. The cytoplasm was packed with different types of inclusions including small food vacuoles, optically opaque granules of different size and shape, but no crystals were detected. Cysts were not found in the cultures. (ref. ID; 4891)
Electron microscopy: Electron microscopic examination showed that the cell coat of this species bore scales. They were generally basket-shaped and looked very like the scales of Paramoeba eilhardi illustrated by Grell & Benwitz (1970). The length of each scale was 400-514 nm, the breadth 170-230 nm and the width about 200 nm. The nucleus had a very distinct structure. At its middle, or somewhat eccentric, a compact rounded mass of electron-dense material was situated measuring about 1.6 um in diameter. It was surrounded by an area of less electron-dense material which formed an irregular, but generally rounded body in the center of the nucleus. In some specimens this body made direct contact with the nuclear envelope, but often there was a distinct space between the body and the nuclear envelope which was filled with patches of electron-dense material. A differentiation of the fibrillar component in the nucleus was not observed; there was no nuclear lamina. With respect to its dimensions and position, the dense central body seems to correspond to the Feulgen-negative lacuna, while the less dense material surrounding it corresponds to the "endosome" which was visible in haematoxylin-stained preparations. No parasome was detected at the electron-microscopical level during the examination of serially-sectioned amoebae. A satisfactory fixation of the cytoplasm and of the organelles was not obtained, but it was possible to conclude that the mitochondria of this species had tubular cristae and an electron-dense matrix. The single large dictyosome was always situated near the nucleus. Rounded lipid bodies were common in the cytoplasm. (ref. ID; 4891)
Remarks
The combination of light- and electron-microscopical features of this species (finger-shaped hyaline pseudopodia ['dactylopodia'], absence of the parasome, radiate floating form, microscales) gives good reason to classify it as a member of the genus Korotnevella (Page, 1981) Goodkov, 1988 (Gymnamoebia, Paramoebidae). Within this genus only two freshwater species -K. bulla and K. stella- have been studied in detail including the use of electron microscopy (Pennick & Goodfellow 1975; Page 1981). Both are clearly distinct from the present species with respect to light-microscopical morphology. Possibly, electron-microscopic study of some strains of Mayorella sensu lato, which are described only from light-microscopic data (Bovee & Sawyer 1979; Page 1983, 1991 and reference therein), will show them to be scale-bearing. Pennick & Goodfellow (1975) illustrated (using TEM) two unidentified marine scale-bearing amoebae (designated as Mayorella sp. 1 and Mayorella sp. 2). The first species has scales which are clearly distinct from those of the present species. There are some similarities between the scales of the present species and those of "Mayorella sp. 2", but the absence of any light-microscopic description of these species leaves no possibility for further comparison. An unidentified parasome-free amoeba strain studied by Grell & Benwitz (1970) has scales closely resembling those of the present species (and of P. eilhardi). But in the case of this species, the authors (op. cit.) stressed a close morphological similarity to P. eilhardi while the present species is much smaller and has different pseudopodia. An unidentified strain studied by Anderson (1977), is more similar to the present species in dimensions and has scales of the same shape, though smaller than those of the present species. The pattern of nucleolar organisation, illustrated by Anderson (1977, p.371) for his strain is different to that described here, but the absence of a light-microscopical description of Anderson's strain does not allow for a more detailed comparison. The above discussion warrants the description of a new species -Korotnevella nivo (the specific name corresponds to the Danish pronunciation of the name of the bay where the species was found). Comparison of the information given by Anderson (1977) and Grell & Benwitz (1970) with the present description suggests that at least three different species of marine Korotnevella exist (given that the strain, studied by Grell & Benwitz is not a parasome-free strain of P. eilhardi). They all seem to show morphological differences, but all have the same general pattern of scales. Scales of P. eilhardi also closely resemble scales of these species. In contrast, two freshwater species, K. stella and K. bulla, each has a distinct scale pattern. Recently a freshwater Korotnevella was isolated and studied (Smirnov, unpublished). It has discoid scales with a conical projection in the middle of each scale. Such scales are different from those of any described species, but they closely resemble those of "Mayorella sp. 3" (Pennick & Goodfellow 1975, Plate 5, Fig. e). This indicates that the taxonomic importance of such features as shape and dimensions of the scales in amoebae needs further detailed study. (ref. ID; 4891)
Type locality
The Sound, Niva Bay (brackish-water, salinity about 15 0/00), Denmark. (ref. ID; 4891)
Type slide
Type slides are deposited at the British Natural History Museum (London, U.K.). Holotype: 1995:2:9:3, Paratype: 1995:2:9:4. This isolate is deposited with the CCAP No. 1543/1. (ref. ID; 4891)
Measurements
Eighty-five live specimens were measured in the culture dishes with the use of a water immersion objective. The length of the locomotive form varied between 19 um and 51 um (mean 39 um); the breadth varied between 14 um and 40 um (mean 21 um). Mean length/breadth ratio (L/B) was 1.9 (range: 0.95-2.8). (ref. ID; 4891)
Descriptions
Freshwater species. (ref. ID; 4891)