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■ Mentioned in the text for comparison; morphometric data from Kaczmarska Sc Fryxell (1986).

Simonsen, 1974, p. 50, Plate 35, Fig. 2; Kaczmarska et al., 1986, p. 1860, Fig. 15; Simonsen, 1992, p. 83, Plate 83, Figs. 5-7. Valve view: Central part with straight or slightly rounded margins varying in length with length of valve. Valve narrowing toward capitate ends. Fibulae, a slightly larger central interspace, and interstriae resolved with LM of acid cleaned mounted valves. Stria structure consisting of one row of areolae, a central nodule, and external canal wall without poroids were observed with EM. Remarks: Nitzschia braarudii and N. bicapitata belong to a large group of species characterized by capitate ends and mainly found in tropical and subtropical open ocean plankton (Hasle, 1960; Simonsen, 1974; Kaczmarska & Fryxell, 1986, 1994; Kaczmarska et al., 1986). Simonsen (1992) examined the type material of N. capitata and isotype material of N. braarudii and concluded that they were conspecific. He also found that the name N. capitata was preoccupied and that therefore the name N. braarudii could be used. Hasle (1960) gave a Latin diagnosis and illustrations of N. braarudii and Equatorial and subantarctic Pacific Ocean as type locality. The description is validated in the Taxonomic Appendix (this chapter) giving the holotype, isotypes and the type locality.

How to identify: Kaczmarska & Fryxell's (1986) investigation demonstrates the problems involved in identifying marine, planktonic Nitzschia species of this group, and also when the fibulae and interstriae of cleaned mounted specimens are visible with LM.

Distribution: Warm water region to temperate. Nitzschia bicapitata has been found between 66°N and 62°S (Hasle, 1976a). Nitzschia braarudii seems to have a more restricted longitudinal distribution.

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