P. granii var. granii

Pseudo-tiitzschia subcurvata (Hasle) G. Fryxell in Fryxell et al. (Plate 73, Table 75)

Basionym: Nitzschia subcurvata Hasle.

References: Hasle, 1964, p. 28, Plate 12, Figs. 14-16, Plate 13, Figs. 1 and 3; Hasle, 1974, p. 426; Hasle 8c Medlin, 1990a, p. 177, Plate 23.2, Figs. 6-8, Fryxell et al., 1991. Girdle view: Overlap of cell ends very short.

Valve view: Middle part (one-fourth to one-half of cell length) dilated, abruptly attenuated toward long, slender projections; one side of valve straight or slightly concave and the other convex, especially in middle part of the valve. Fibulae of irregular distances, interstriae not resolved with LM.

Remarks: The species was transferred to the section Pseudo-nitzschia by Fryxell et al. (1991) based on type of colony formation, valve shape, and the nature of the raphe and fibulae.


P. granii—northern cold water region to temperate? P. cuspidata—warm water region to temperate. P. prolongatoides, P. subcurvata, and P. turgiduloides—southern cold water region.

P. turgidula, P. lineola, and P. inflatula—cosmopolitan. The information on distribution is mainly from Hasle (1964, 1965b) and represents only fragmentary observations. Pseudo-nitzschia delicatissima and P. pseudodelicatissima are common, occasionally as the predominant diatom species, in North Atlantic plankton, and may be cosmopolitan although without reliable identifications from the Antarctic. Pseudo-nitzschia granii was described from the Norwegian Sea and has most probably a wide distribution in the North Atlantic region. Small needle-shaped Nitzschia species in or on Phaeocystis colonies have been reported from the Norwegian Sea and the North Sea since the beginning of this century (see Hasle, 1964, p. 30). In July, 1988 it was found together with Phaeocystis as far north as the King's Bay, Spitzbergen, ca. 80°N (G. Hasle and B. Heimdal, personal observations). How to identify: In general, single valves mounted in a medium of a high refractive index examined with an oil immersion lens under darkfield or phase contrast illumination are required to identify the Nitzschia

PLATE 73 Nitzschia americana: valves showing size variation and fibulae. Pseudo-nitzschia subcurvata: valve with fibulae. Pseudo-nitzschia prolongatoides: (a) partial chains in valve and girdle views; (b) valve with fibulae and central larger interspace. Pseudo-nitzschia granii: var. granii: Valves, size variation, fibulae. Scale bars = 10/xm.

delicatissima complex to species. In these circumstances the fibulae are resolved, and in some species the interstriae are also resolved. The structure of the striae is discernible in coarsely silicified specimens of a few species. Remarks: Takano (1993) described Nitzschia multistriata from inlets of southern Japan, forming a bloom in summer 1991. It forms stepped chains, has no central nodule, more interstriae than fibulae, valve striae with two rows of circular poroids, and is thus similar to P. delicatissima except for the lack of a central nodule. Takano (1995, p. 74) made the new combination Pseudo-nitzschia multistriata.

lncertae sedis (Nitzschia)

With the exception of Nitzschia longissima, records of the following species are in recent literature. Their morphology is poorly known and, as a consequence, so is their taxonomy. Our EM observations are fragmentary but are used here as a starting point for further investigations. As far as we have observed these species all have an eccentric raphe; they are marine and occur in plankton although that may not be their primary habitat.

A. Valve outline linear to lanceolate to slightly rostrate. Nitzschia americana Hasle (Plate 73)

References: Hasle, 1964, p. 41, Plate 14, Figs. 13-19; Hasle, 1993, p. 318. Girdle view: Linear.

Valve view: Linear with slightly convex margins; valve ends obtusely rounded. Fibulae more conspicuous than interstriae. Striae with two rows of small poroids (EM). Remarks: Nitzschia americana is probably primarily epiphytic on Chaetoceros setae (G. Hasle and E. Syvertsen, personal observations) and possibly epiphytic on other diatoms. Being confused with a mophologically similar, probably undescribed species occurring in stepped colonies, N. americana was incorrectly transferred to Pseudo-nitzschia (Hasle, 1993). Mophomeric data: Apical axis, 16-40 fim; transapical axis, ca. 3 /xm; 18-20 fibula and 27-30 striae in 10 /xm. Distribution: Cosmopolitan (?).

PLATE 74 Nitzschia sicula: valves, var. bicuneata to the left, var. rostrata to the right. Nitzschia longissima: (a) whole cell; (b) valve view. Nitzschia bicapitata: valve with striae and central larger interspace. Nitzschia braarudii: valve with striae and slightly central larger interspace. Scale bars = 10 pm.

NitzsGhfa var. bicuneata

N. sicula var. rostrata

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