PLATE 68 Fragilariopsis rhombica: two valves of different size, biseriate striae indicated in smaller valve. Fragilariopsis separanda: two valves, uniseriate striae indicated in smaller valve. Fragilariopsis cylindrus: (a) ribbon in girdle view, chloroplasts in top cell; (b) valves showing size variation. Fragilariopsis cylindriformis: valves showing variation in size and outline. Fragilariopsis curta: valves of different size and heteropolarity. Scale bars = 10 fim.
Fragilariopsis separanda Hustedt (Plate 68, Table 73) Synonym: Nitzschia separanda (Hustedt) Hasle.
References: Hustedt, 1958a, p. 165, Figs. 108-112; Hustedt, 1958b, p. 207, Figs. 18 and 19; Hasle, 1965a, p. 26, Plate 9, Figs. 7-10; Hasle, 1972c, p. 115; Hasle 8c Mediin, 1990b, p. 181, Plate 24.4, Figs. 7-10. Valve view: Larger (25-30 fim) specimens broadly linear with pointed ends and smaller specimens elliptical to lanceolate. Transverse striae with one row of poroids. Otherwise as described for F. rhombica.
B. Valves linear to sublinear.
1. Apical axis isopolar.
Fragilariopsis cylindrus (Grunow) Krieger in Helmcke 8c Krieger (Plate 68, Table 73)
Basionym: Fragilaria cylindrus Grunow in Cleve. Synonym: Nitzschia cylindrus (Grunow) Hasle. References: Grunow in Cleve 8c Möller, 1882, No. 314; Cleve, 1883, p. 484, Plate 37, Figs. 64a-64c; Helmcke 8c Krieger, 1954, p. 17, Plate 187; Hustedt, 1958a, p. 162, Figs. 145 and 146; Hustedt, 1959, p. 152, Fig. 665; Hasle, 1965a, p. 34, Plate 12, Figs 6-12; Hasle, 1968c, Fig. 6; Hasle, 1972c, p. 115; Hasle 8c Medlin, 1990b, p. 181, Plate 24.6, Figs. 6-12, Plate 24.8, Figs. 11-13. Girdle view: Cells rectangular; pervalvar axis fairly short. Cells in ribbons with no interspace between valves of sibling cells. Valve view: Straight, parallel margins; broadly rounded, almost semicircular apices. Transverse interstriae straight in the rectangular part of the valve; oblique ribs from the last interstria toward the rounded apex usually too weakly silicified to be resolved with LM. Distinction between fibulae and interstriae readily seen with LM. No central larger interspace. Stria structure not resolved with LM.
Fragilariopsis cylindriformis (Hasle, in Hasle 8c Booth) Hasle (Plate 68, Table 73)
Basionym: Nitzschia cylindroformis Hasle in Hasle 8c Booth. References: Booth et al., 1982, Figs. 7-12 as N. cylindrus; Hasle 8c Booth, 1984; Hasle 8c Medlin, 1990b, p. 181, Plate 24.8, Figs. 4-10; Hasle, 1993, p. 316.
Girdle view: Cells in ribbons with no interspace between valves of sibling cells.
Valve view: Largest specimens linearly oblong (similar to F. cylindrus), medium-sized specimens narrowly elliptical to lanceolate (like F.
pseudonana), and the smallest specimens broadly elliptical to subcircular. Fibulae and interstriae resolved with LM with fibulae more distinct than interstriae. Interstriae parallel and straight, except close to the poles. No central larger interspace.
Fragilariopsis curta (Van Heurck) Hustedt (Plate 68, Table 73) Basionym: Fragilaria curta Van Heurck. Synonym: Nitzschia curta (Van Heurck) Hasle. References: Van Heurck, 1909, p. 24, Plate 3, Fig. 37; Hustedt, 1958a, p. 160, Figs. 140-144, 159; Hustedt, 1958b, p. 201, Figs. 2-4; Hasle, 1965a, p. 32, Plate 12, Figs. 2-5; Hasle, 1972c, p. 115; Hasle 8c Medlin, 1990b, p. 181, Plate 24.6, Figs. 2-5. Valve view: Apical axis heteropolar with one pole slightly narrower than the other. Valve margins more or less parallel, tapering toward the narrower of the two broadly rounded poles. Interstriae and fibulae readily observed with LM; fibulae coarser than interstriae. Interstriae straight in middle part of valve and curved near the poles with some additional apical ribs, these ribs as well as stria structure just visible with LM. No central larger interspace.
C. Valves semilanceolate.
Fragilariopsis doliolus (Wallich) Medlin 8c Sims (Plate 69) Basionym: Synedra doliolus Wallich.
Synonym: Pseudoeunotia doliolus (Wallich) Grunow in Van Heurck. References: Wallich, 1860, p. 48, Plate 2, Fig. 19; Van Heurck, 1880-1885, Plate 35, Fig. 22; Cupp, 1943, p. 190, Fig. 140; Hustedt, 1958b, p. 199, Fig. 1; Hustedt, 1959, p. 259, Fig. 737; Hasle, 1972c, Fig. 9; Hasle 1976a, Figs. 29-31; Medlin 8c Sims, 1993. Girdle view: Cells rectangular in broad girdle view, united into curved ribbons by the valve surfaces; no interspace between sibling cells. Open bands, three unperforated and one with one row of perforations (Medlin 8c Sims, 1993). Chloroplasts—two plates, one on either side of the median transapical plane.
Valve view: Valves semilanceolate with bluntly rounded ends. One side of valve (ventral) straight and seldom slightly convex; the other side (dorsal) more strongly convex, gradually decreasing toward the ends, and near the ends often slightly constricted. Transverse striae with two alternating rows of poroids (LM). Interstriae thickened vertically on external and internal surfaces of valve face and mantle (SEM). Canal raphe (SEM)
Psaudo-nitzschia seriata f. seriata
P. pungens along bend between valve face and mantle, along either dorsal or ventral side, indicating a diagonal location of the raphe systems on the frustule. Some irregularities between the middle fibulae observed with LM and SEM.
Remarks: SEM investigations (Hasle, 1976a) confirmed Hustedt's (1958b) LM observation of a canal raphe in F. doliolus; central raphe endings, reported by Hustedt, were not seen (see also Medlin & Sims, 1993). The expressed curvature giving the ribbons the appearance of a section of a barrel may be due to a more shallow valve mantle along the straight rather than the curved valve margin.
F. kerguelensis, F. ritscheri, F. rhombica, and F. separanda—southern cold water region, plankton.
F. atlantica and F. cylindriformis—northern cold water region, plankton.
F. doliolus—warm water region.
F. pseudonana—cosmopolitan, plankton.
F. curta—southern cold water region, plankton and ice.
F. oceanica—northern cold water region, plankton and ice(?).
F. cylindrus—southern and northern cold water regions, plankton and ice.
Fragilariopsis kerguelensis is particularly abundant in the southern ocean but has been recorded as far north as the Cape Verde Islands (Heiden &c Kolbe, 1928).
How to identify: Fragilariopsis doliolus is readily identified in colonies and as single cells in water mounts due to the unique shape of the ribbons and the valve outline. Fragilariopsis kerquelensis may be discriminated from other planktonic species by its coarse silification, also when observed in girdle view. The other planktonic species have to be examined in valve view to secure a positive identification. Material cleaned of organic matter and mounted in a medium of a high refractive index may be required.
Genus Neodenticula Akiba &c Yanagisawa 1986
Type: Neodenticula kamtschatica (Zabelina) Akiba & Yanagisawa.
Basionym: Denticula kamtschatica Zabelina.
PLATE 69 Neodenticula seminae: (a) single cell in girdle view with pseudosepta; (b) valves with striation and pseudosepta and valve with attached band. After Simonsen &C Kanaya (1961). Fragilariopsis doliolus: (a) ribbon in broad girdle view; (b) valve with striation and areolae indicated. After Cupp (1943). Pseudo-nitzschia seriata f. seriata: (a) stepped chains in valve and girdle views; (b) valve view. From Hasle (1972d). Pseudo-nitzschia australis: valves of different size. From Hasle (1972d). Pseudo-nitzschia pungens: partial chains in (a) girdle view and (b) valve view. From Hasle (1972d). Scale bars = 10 /u,m.
Terminology specific to Neodenticula:
Pseudoseptum—diaphragm-like ingrowth of valve, in this genus shaped as a vertical wall penetrating into the cell interior and separating the lumen of the valve into chambers.
Neodenticula seminae (Simonsen 8c Kanaya) Akiba 8c Yanagisawa (Plate 69) Basionym: Denticula seminae Simonsen 8c Kanaya. Synonyms: Denticula marina Semina; Denticulopsis seminae (Simonsen 8c Kanaya) Simonsen.
References: Semina, 1956, p. 82, Figs. 1 and 2; Simonsen 8c Kanaya, 1961, p. 503, Plate 1, Figs. 26-30; Hasle, 1972c, Figs. 3, 4, and 8; Simonsen, 1979, p. 65; Semina, 1981b; Akiba 8c Yanagisawa, 1986, p. 491, Plate 24, Figs. 1-11, Plate 26, Figs. 1-10; Yanagisawa 8c Akiba, 1990, p. 263, Plate 7, Figs. 45-49; Medlin 8c Sims, 1993, Figs. 13-21. Girdle view: Cells rectangular with rounded corners, interstriae, and strong pseudosepta, the latter widening toward cell interior. Bands septate.
Valve view: Valves linear to elliptical, usually with broadly rounded ends. Valve surface with transverse striae, the areolation of the striae usually too fine to be resolved with LM. Pseudosepta seen as sharp, distinct lines with focus on external valve surface and as wide crossbars with focus on their distal parts; both ends of a crossbar connected with the thick valve wall by a suture. Pseudosepta sometimes short in pervalvar direction and without crossbars. A varying number of striae between two pseudosepta. One interstria often branched into two fibulae (SEM). Raphe continuous along the edge of valve face scarcely discernible with LM. Raphe systems of the two valves on opposite sides of the frustule. Morphometric data: Apical axis, 10-60 /am, transapical axis, 4-9 ¿im; pseudosepta, 2-4 in 10 fim; 1-4 striae and interstriae between two pseudosepta and 8-12(?) fibulae in 10 ju,m.
Distribution: Common in North Pacific Ocean, also reported from tropical parts of the Indian and Pacific Oceans (Semina, 1981b).
How to identify: The species may be identified as whole cells in water mounts.
Remarks: Controversial opinions exist concerning the crossbars being parts of the pseudosepta and thus of the valves or of the valvocopula septum. Based on our own published and unpublished observations we agree with Simonsen (1979) and Akiba 8c Yanagisawa (1986) that although the bands are septate, the crossbars do belong to the pseudosepta. Another peculiarity is the presence of open and closed bands in N. seminae (Hasle, 1972c, Fig. 4; Akiba 8c Yanagisawa, 1986, Plate 24, Figs. 6 and 7, Plate 26, Figs. 7 and 8; Yanagisawa 8c Akiba, 1990, Plate 7, Fig. 49; Medlin 8c Sims, 1993, Figs. 15, 16, 20, and 21). Medlin 8c Sims (1993) suggested that the closed bands might be more commonly associated with valves with deeper pseudosepta.
Genus Pseudo-nitzschia H. Peragallo in H. & M. Peragallo Lectotype: Pseudo-nitzschia seriata (Cleve) H. Peragallo (in H. & M. Peragallo, 1897-1908) (vide Fryxell et al., 1991, p. 243).
The genus was erected for Nitzschia sicula with the varieties bicuneata and migrans, and Nitzschia seriata with the variety fraudulenta—all pelagic forms with obscure keels ("carènes très obscures"), if present at all (H. & M. Peragallo, 1897-1908, p. 263). Pseudo-nitzschia seriata was furthermore characterized by a fine striation and cells in long filaments, and N. sicula by coarser striation and cells probably free living. The raphe system of Pseudo-nitzschia as revealed with EM is like that of Fragilariopsis, not being elevated above the general level of the valve, and lacking conopea and lacking poroids in the external canal wall. Some of the species have striae with two rows of poroids like Fragilariopsis, whereas others have more than two rows and still others have only one row. Some Pseudo-nitzschia species are rectangular in girdle view like Fragilariopsis, but many are fusiform, and in valve view in general longer and narrower than Fragilariopsis. The distinction between the two genera is especially manifest in the stepped colonies and in the tendency of heteropolarity of the transapical axis of Pseudo-nitzschia. The girdle structure may be a third distinctive character. The intercalary bands of Pseudo-nitzschia are open, distinctly pointed, narrow, and mostly striated. The striae are similar in structure to those on the valve with one or more rows of poroids (Hasle, 1965b; Hasle et al., 1995). This type of band structure together with other morphological characters such as the structure of the raphe system, characterize Pseudo-nitzschia as a natural group separate from Nitzschia (Hasle, 1994).
Pseudo-nitzschia is a geographically widely distributed genus (Hasle, 1965b, 1972d) restricted to marine plankton. More detailed studies of the distribution of taxa referred to Pseudo-nitzschia spp. are of special interest, however, since P. multiseries is well established as being capable of producing the neurotoxin, domoic acid, in growth-limiting conditions in stationary stage. This has been reported from at least two areas with different climatic and hydrographie conditions (Bates et al., 1989; Fryxell et al., 1990). Domoic acid was also detected in clams and mussels in the Bay of Fundy, eastern Canada, at a time when P. pseudodelicatissima was the predominant phytoplankton species (Martin et al., 1990), and P. australis has been documented as a producer of domoic acid in California waters (Buck et al., 1992; Garrison et al., 1992). Pseudo-nitzschia delicatissima and P. seriata have been shown to produce domoic acid in cultures (Smith et al., 1991; Lindholm et al., 1994). Domoic acid may be a worldwide threat, on temperate coasts at least, but action can be taken to alleviate the potential danger by monitoring the phytoplankton and utilizing temporary closings of selected fisheries in target areas when necessary for the duration of a bloom.
Cells strongly elongate, rectangular, or fusiform in girdle view.
Cells in stepped chains united by shorter or longer overlap of valve ends. Chains motile. Raphe strongly eccentric.
Raphe not raised above the general level of the valve.
Valve face interstriae often more than one to each fibula.
Central larger interspace in most species.
Valve face slightly curved or flattened, not undulated.
Valve narrowly lanceolate to fusiform and linear with rounded or pointed ends. Transapical axis heteropolar in some species. Stria structure usually too delicate to resolve with LM. Chloroplasts—two plates, lying along the girdle, one on either side of the median transapical plane. Resting spores unknown.
Characters showing differences between species: Valve outline.
Width of valve (= length of transapical axis).
Polarity of transapical axis.
Linear density of interstriae versus fibulae.
Size of central interspace.
Shape of valve ends in girdle and valve views.
Length of overlap of cell ends.
KEY TO SPECIES (based on light microscope observations)
1 a. Transapical axis wider than 3 /¿m 2
lb. Transapical axis narrower than 3 fim 9
2a. Central larger interspace present 3
2b. Central larger interspace absent 6
3a. Outline of valve asymmetrical in the apical axis; one margin almost straight, the other curved 4
3b. Outline of valve symmetrical in the apical axis 5
4a. Fibulae and interstriae discernible with the light microscope . P. heimii
4b. Fibulae but not interstriae discernible with the light microscope
5a. Valve outline lanceolate; margins not parallel; fibulae and interstriae equal in number P. fraudulenta
5b. Valve outline with parallel margins for the greater part of the valve length; fibulae and interstriae unequal in number . . P. subfraudulenta 6a. Outline of valve asymmetrical in the apical axis; one margin almost straight, the other curved P. seriata
6b. Outline of valve symmetrical in the apical axis 7
7a. The presence of poroids in the striae discernible with the light microscope
7b. The presence of poroids in the striae not discernible with the light microscope 8
8a. Transapical axis wider than 5 ftm; valve apices rostrate; outline of smaller valves tends to be asymmetrical in the apical axis P. australis
8b. Transapical axis narrower than 5 fxm; valve outline lanceolate with pointed (not rostrate) apices P. multiseries
9a. Central larger interspace present 10
9b. Central larger interspace absent, valve with prolonged projections (rostrate) 17
10a. Valve inflated in the middle 11
10b. Valve otherwise 14
11a. Valve with prolonged projections P. prolongatoides lib. Valves otherwise 12
12a. Valves slightly inflated before tapering ends, interstriae not discernible with the light microscope P. inflatula
12b. Valve ends obtuse, interstriae distinct 13
13a. Valves comparatively wide (length ca. 12-30 times width), valve ends broadly obtuse P. turgidula
13b. Valves narrow (length ca. 27-60 times width) P. turgiduloides
14a. Valves comparatively wide (ca. 3 /¿.m) and tapering parts of valves long
14b. Valves otherwise 15
15 a. Valves slightly lanceolate, fibulae and central larger interspace barely visible with the light microscope, interstriae not visible
15b. Valves linear, tapering parts of valves short 16
16a. Fibulae and central larger interspace clearly visible with the light microscope, interstriae also occasionally visible P. pseudodelicatissima
16b. Fibulae and interstriae clearly visible with the light microscope
17a. One valve margin straight or slightly concave, the other convex, especially in the middle part of the valve P. subcurvata
17b. Valve narrow, lanceolate to needle shaped P. granii
The species may also be grouped according to numerical data, shape of valves and stria structure, the latter mainly revealed with TEM.
A. Valves fairly wide compared to length (transapical axis ca. 3 fim or more).
1. Approximately equal numbers of fibulae and interstriae; fibulae therefore often indistinct; no central larger interspace: P. seriata, P. australis, P. pungens, and P. multiseries (Table 74).
2. Slightly more interstriae than fibulae; central larger interspace present: P. pungiformis, P. fraudulenta, and P. subfraudulenta (Table 74).
3. More than one interstria per fibula; central larger interspace present; transapical axis heteropolar: P. heimii and P. subpacifica (Table 74).
B. Valves narrow compared to cell length (transapical axis ca. 3 /am or less); approximately two interstriae for each fibula.
1. Circular poroids.
Central larger interspace present: P. delicatissima, P. lineola, P. prolongatoides, P. turgidula, and P. turgiduloides (Table 75).
2. Square poroids.
a. Central larger interspace present: P. cuspidata, P. pseudodelicatissima, and P. inflatula (Table 75).
b. No central larger interspace: P. granii and P. subcurvata (Table 75).
A. Transapical axis ca. 3 /xm or more.
This group of larger (= wider in valve view) Pseudo-nitzschia species has been called the "Nitzschia seriata complex" (Hasle, 1965b). They all have a tendency to appear in girdle view in water mounts, and with P. pungens as the only possible exception, the distinction between species can only be seen in valve view. Pseudo-nitzschia seriata seems for some obscure reasons to have been regarded by many planktonologists as the only species of this size group appearing in stepped chains. The whole group may have been identified as "Nitzschia seriata" on many occasions, and the numerous records of N. seriata from all oceans should be regarded with sceptisism.
1. Approximately equal numbers of interstriae and fibulae; no central larger interspace.
Pseudo-nitzschia seriata (Cleve) H. Peragallo in H. 8c M. Peragallo f. seriata (Plate 69, Table 74) Basionym: Nitzschia seriata Cleve.
References: Cleve, 1883, p. 478, Fig. 75; H. 8c M. Peragallo, 1897-1908, p. 300, Plate 72, Fig. 28; Cupp, 1943, p. 201, Fig. 155; Hasle, 1965b, p. 8, Plate 1, Fig. 1, Plate 3, Figs. 1-7 and 10; Hasle 8c Medlin, 1990c,
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