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Nitzschia sicula (Castracane) Hustedt var. sicula, N. sicula var. rostrata Hustedt; N. sicula var. bicuneata Grunow in Cleve 8c Möller Hasle; N. sicula var. migrans (Cleve) Hasle (Plates 74 and 75, Table 76) Basionyms: Synedra sicula Castracane; Rhaphoneis} (Raphoneis) Diatoma? bicuneata Grunow in Cleve 8c Möller; Nitzschia migrans Cleve. Synonyms: Pseudo-nitzschia sicula (Castracane) H. Peragallo (in H. 8c M. Peragallo, 1897-1908); Pseudo-nitzschia sicula var. bicuneata (Grunow in Cleve 8c Möller) H. Peragallo in H. 8c M. Peragallo; Pseudo-nitzschia sicula var. migrans (Cleve) H. Peragallo in H. 8c M. Peragallo. References: Castracane, 1875, p. 34, Plate 6, Fig. 7; Cleve 8c Möller, 1879, Nos. 208-210; Cleve, 1897b, p. 300, Fig. 9; H. 8c M. Peragallo, 1897-1908, p. 299, Plate 72, Figs. 25-27, Plate 82, Fig. 28; Heiden 8c Kolbe, 1928, p. 671; Hustedt, 1958a, p. 180, Figs. 128-132; Hasle, 1960, p. 26, Fig. 16; Hasle, 1964, p. 38, Figs. 11-13, Plate 5, Fig. 8, Plate 13, Figs. 14a and 14b, Plate 14, Fig. 22, Plate 16.

The varieties differ in valve outline, particularly in the shape of the apices. The eccentric canal raphe, the flattened, not undulated valves with a fairly coarse striation, and the equal numbers of fibulae and interstriae are common features. These diatoms have been recorded from widespread localities but evidently in small cell numbers which may be the reason why their fine structure, taxonomy and distribution are poorly known.

Nitzschia sicula var. sicula, var. bicuneata, and var. rostrata are lanceolate in valve outline with slightly rounded apices; the nominate variety has more obtuse ends, var. bicuneata has slightly protracted apices, and var. rostrata has rostrate valve ends. Nitzschia sicula var. migrans differs from the other varieties by being linear in the greater part of the valve length. Central raphe endings in a circular depression, a complex stria structure differing along the valve length, consisting of rows of small poroids close to the interstriae, and the absence of poroids in the external canal wall were documented with TEM and SEM (Plate 75, a-d; Hasle, 1964). Distribution: Probably warm water region to temperate.

How to identify: These diatoms may be identified in water mounts in valve view but not in girdle view.

Remarks: Hustedt (1958a) made the combination Nitzschia sicula (Castracane) Hustedt. If, however, Pseudo-nitzschia was regarded as a separate genus, P. sicula was, in his opinion, the correct name. Mann (1978), on the other hand, found no problems in accomodating N. sicula in Fragilariopsis. In light of the present information on the stria structures of Pseudo-nitzschia and Fragilariopsis, in addition to no observations of a possible chain formation in N. sicula, we prefer to retain the species with its varieties in Nitzschia. We have no educated opinion, however, as to which section it belongs.

Nitzschia marina Grunow in Cleve 8c Grunow (Plate 75)

Basionym: Nitzschia angustata var. marina Grunow in Cleve 8c Möller, (N.

angusta var. marina Cleve 8c Grunow, 1880, p. 70).

Synonyms: Synedra gaussi Heiden in Heiden 8c Kolbe; Pseudo-nitzschia hustedtii Meister.

References: Cleve 8c Möller, 1878, Nos. 154 and 155; Cleve 8c Grunow, 1880, p. 70; Van Heurck, 1880-1885, Plate 57, Figs. 26 and 27; H. 8c M. Peragallo, 1897-1908, p. 272, Plate 72, Fig. 24; Heiden 8c Kolbe, 1928, p. 561, Plate 5, Fig. 112; Meister, 1937, p. 272, Plate 11, Fig. 2; Kolbe, 1954, p. 40, Plate 3, Figs. 38-40; Kolbe, 1957, p. 39, Plate 1, Fig. 7; Simonsen, 1992, p. 22, Plate 18, Figs. 1-7. Valve view: Linear to lanceolate with rounded apices. Valve wall extremely coarsely silicified. Valve mantle high and rounded. Valve face and mantle similar in structure: externally with biseriate striae and slightly raised interstriae. Striation just discernible with LM. Raphe not raised above valve surface; external canal wall unperforated except for the raphe slit. Fibulae strong and curved as seen on valves in internal views. Valve wall apparently double layered, the internal layer unperforated except for one row of holes along the non-raphe bearing margin. Morphometric data: Apical axis, 53-353 /xm; transapical axis, 8-12 jum, fibulae and striae, 10-12 in 10 /xm. Distribution: Warm water region.

Nitzschia kolaczeckii Grunow

References: Grunow, 1867, p. 18; Grunow, 1877, p. 173, Plate 94, Fig. 10; Hustedt in A. Schmidt, 1924, Plate 349, Figs. 38 and 39; Kolbe, 1955, p. 174, Plate 2, Figs. 22 and 23; Hasle, 1960, p. 24, Plate 5, Figs. 50a-50c. Valve view: lanceolate with slightly outstretched apices. The two raphes of a frustule diagonally located. Central interspace slightly larger than the rest. Valve with three stria systems, one transverse and two oblique ones as in Pleurosigma.

Morphometric data: Apical axis, 67-120 (im; transapical axis, 7.511 m; eight or nine fibulae in 10 /¿m; 13-16 oblique, and.17-18 transverse striae in 10 ¿im. Distribution: Warm water region.

How to identify: Nitzschia marina and N. kolaczeckii may be identified in water mounts in valve view but most likely not in girdle view. Remarks: Cleve 8c Grunow (1880) placed N. marina in Tryblionella and N. kolaczeckii in Lanceolatae. Nitzschia sicula and N. marina have similar valve and raphe structures as seen with LM. There is also a certain similarity between the two species in external valve structure as revealed with SEM. Information on the internal valve structure of N. sicula is lacking, however. The only available information on the valve structure of N. kolaczeckii is from LM investigations. Based on light micrographs (Hasle, 1960, Plate 5, Fig. 50c) it may be assumed that the central circular depression with raphe endings is also present in N. kolaczeckii.

B. Valves with prolonged projections.

Nitzschia longissima (Brebisson, in Kutzing) Ralfs in Pritchard (Plate 74) Basionym: Ceratoneis longissima Brebisson in Kutzing. References: Kutzing, 1849, p. 891; Pritchard, 1861, p. 783, Plate 4, Fig. 23; Cupp, 1943, p. 200, Fig. 154; Hendey, 1964, p. 283; Hasle, 1964, p. 20, Plate 10, Figs. 5-7; Hasle 8c Medlin, 1990a, p. 177, Plate 23.1, Figs. 5-7.

Valve view: Linear to lanceolate, tapering to very long projections. Raphe with fibulae and central larger interspace distinct in mounted cleaned material. External canal wall poroid (TEM). Transverse striae and interstriae hardly visible with LM. Morphometric data: Apical axis, 125-450 ¿t,m; transapical axis, 6-7 [im; fibulae 6-14? in 10 pim; striae, ca. 16 in 10 /j,m (Cupp, 1943), 52-60 in 10 pan (Hasle, 1964).

Distribution: Cosmopolitan (?), inshore waters.

How to identify: As mentioned previously C. closterium and N. longissima may easily be confused when examined as entire cells in water mounts. Acid-cleaned material mounted in a medium of a high refractive index, or often EM observations, may be needed to distinguish between the extremely weakly silicified C. closterium with the numerous narrow bands and the simple canal raphe and the more coarsely silicified N. longissima with fibulae connected with silicified strips running parallel to the raphe slit (Hasle, 1964, Plate 10).

Remarks: Detailed morphological studies are needed before a good definition of this and similar freshwater and brackish water species can be given. Cleve 8c Grunow (1880, p. 100) placed N. longissima in Nitzschiella, which they characterized as a group with "Schalen mit excentrischem Kiele und lang vorgezogenen Spitzen."

C. Valves with capitate ends.

Nitzschia bicapitata Cleve (Plate 74, Table 77) References: Cleve, 1901b, p. 933, Fig. 12; Hustedt, 1958a, p. 169, Figs. 176-190; Hasle, 1960, p. 21, Fig. 10; Hasle, 1964, p. 37, Plate 5, Fig. 7, Plate 14, Figs. 8-12, Plate 15, Figs. 3-6; Simonsen, 1974, p. 50, Plate 35, Figs. 3-15; Kaczmarska 8c Fryxell, 1986, p. 242, Fig. 4; Kaczmarska et al., 1986, p. 1859, Fig. 10. Valve view: Valves lanceolate with capitate ends less pronounced in smaller specimens. Fibulae and central larger interspace readily observed on cleaned mounted valves; striae with one row of areolae discernible on well silicified specimens. Central nodule and external canal wall without poroids observed with EM. Remarks: Kaczmarska 8c Fryxell (1986, p. 237) carried out a detailed morphological study of "the diatom known in the literature as Nitzschia bicapitata CI." SEM investigations showed three morphotypes of N. bicapitata Cleve sensu lato and a new species, N. bifurcata Kaczmarska 8c Licea. The epithet of the new species refers to the stria structure revealed with SEM. Whereas the rest of the N. bifurcata valve has striae with one row of areolae, like in N. bicapitata, the margin opposite to the raphe has two rows of alternating small pores.

Nitzschia braarudii Hasle (Plate 74, Table 77) Synonym: Nitzschia capitata Heiden in Heiden 8c Kolbe. References: Heiden 8c Kolbe, 1928, p. 666, Plate 7, Fig. 151; Hasle, 1960, p. 22, Fig. 11, Plate 7, Figs. 58-63; Hasle, 1964, p. 35, Plate 2, Fig. 1, Plate 14, Fig. 20, Plate 15, Figs. 1 and 2; Taylor, 1967, p. 450, Fig. 30;

TABLE 77 Morphometric Data of Nitzschia spp.

Spccies/author

Transapical axis Apical axis (pm) (pm)

Striae in Fibulae in 10 pm 10 pm

N. bicapitata Cleve, 1901b

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