Note. Length is measured along the more straight margin of the valve; width is the greatest distance from the curved to the more straight margin of the valve.

Note. Length is measured along the more straight margin of the valve; width is the greatest distance from the curved to the more straight margin of the valve.

seen with LM in cleaned material as are the morphological distinctive structures of the two Hemidiscus species.

Genus Roperia Grunow ex Pelletan 1889 (Plate 22) Type: Roperia tesselata (Roper) Grunow ex Pelletan. Basionym: Eupodiscus tesselatus Roper.

References: Roper, 1858, p. 19, Plate 3, Fig. 1; Van Heurck, 1880-1885, Plate 118, Figs. 6 and 7; Hustedt, 1930, p. 523, Fig. 297; Hendey, 1964, p. 85, Plate 22, Fig. 3; Fryxell et al. 1986b, p. 24, Figs. 25, 32-3, 32-4; Lee & Lee, 1990.

Valve outline circular to ovate. Marginal ring of processes—all similar in size and shape. Pseudonodulus prominent. Central and marginal part of valve usually different in areolation. Morphometric data: Diameter, 40-70 /xm; valve areolae, six in 10 /¿m in central part, somewhat smaller near margin; marginal processes, two in 10 pan (Hustedt, 1930).

Distribution: Recorded as far north as 66°N in the Norwegian Sea and as far south as 57°S in the subantarctic Pacific by Hasle (1976a) who, with doubt, classified it as a warm water species. The paucity of records from the Pacific Ocean as well as from the western part of the Atlantic Ocean north of 30°N made the classification "cosmopolitan" just as doubtful.

Incertae sedis (Hemidiscaceae)

Genus Pseudoguinardia von Stosch 1986 Type: Pseudoguinardia recta von Stosch. Monotypic genus.

Pseudoguinardia recta von Stosch (Plate 22) Reference: von Stosch, 1986, p. 307, Figs. 7-11. Girdle view: Cells cylindrical in long straight colonies. Bands with poroids (TEM) numerous, open, not or barely discernible with LM. Chloroplasts numerous, subglobular with a large globular pyrenoid.

Valve view: Valve outline circular. Valve face flat; mantle low and rounded. Pseudonodulus close to valve margin, discernible (LM) in valve view as a circular hyaline area. Marginal ring of small labiate processes (SEM) and one larger labiate process discernible (LM) as a small nodule in girdle view. Valve face structure composed of faint, branched lines oriented toward a diameter (a line) combining pseudonodulus and the large labiate process (LM). Scattered poroids on valve face and mantle (TEM).

Morphometric data: Pervalvar axis, 93-270 /xm; diameter, 26-83 jum; ratios of pervalvar axis to diameter, 3.0-6.7 in smaller and 1.6-3.9 in larger cells.

Distribution: Warm water region—listed by von Stosch (1986) from Australian waters, the Indian Ocean, coastal waters off Northwest Africa, off Portugal, both coasts of Florida and the Mediterranean Sea. Other records are from Columbian and Californian coastal waters (G. Hasle, personal observations) and from the Gulf Stream warm core rings (Fryxell, personal communication).

How to identify: Pseudoguinardia recta is easily recognized in chains and as single whole cells in girdle view in water mounts; single valves are also recognizable with LM on permanent mounts.

Remarks: Von Stosch (1986) assigned Pseudoguinardia a provisional place in Hemidiscaceae on the assumption that the structures interpreted as a pseudonodulus and labiate processes were correctly named. As evident from the generic characters, particularly the numerous structured bands and the valve structure, it differs from the four genera assigned to Hemidiscaceae in this chapter on most or all other characters. No other described family can be pointed out as the right place for this species. In the past P. recta has most probably been identified as Guinardia flaccida or Leptocylindrus sp. It differs (LM) from G. flaccida by the straight chains, the indistinct bands, the presence of the pseudonodulus, the shape and number of labiate processes, and the orientation of the valve structure, and from Leptocylindrus spp. by the two latter features as well as by the greater size. A TEM picture of P. recta, identified as Lauderiopsis costata, is provided in Sundstrom (1986, Plate 39, Fig. 291). Lauderiopsis costata Ostenfeld was described with the ends of the numerous, very distinct bands forming "a slowly twined line" (Ostenfeld & Schmidt, 1901, p. 159) in contrast to the bands of P. recta being "hardly visible in water mounts" and with openings and ligulae forming "two opposite straight rows" (von Stosch, 1986, p. 313).

Family Asterolampraceae H. L. Smith 1872 emend. Gombos 1980

In the classification of Round et al. (1990) this family constitutes a separate order, Asterolamprales Round & Crawford, whereas Simonsen (1979) as well as Glezer et al. (1988) placed it in the order Centrales.

The family is characterized (Fig. 14) by "a partially areolated valve surface, which exhibits varying modes of development of hollow, hyaline rays that open to the interior of the valve by way of elongate slit-like openings and open to the exterior of the valve through holes at the marginal ends of the rays" (Gombos, 1980, p. 227). The hyaline rays extend from a hyaline (nonareolate) central area and terminate short of the valve margin in a labiate process (spine; apiculus in the older literature). The central area is traversed by a number of straight, zig-zaged, or branched lines termed umbilical lines (Greville, 1860) or separating lines (Gombos, 1980). Due to the raised hyaline rays the valve surface is radially undulated, and the cell is otherwise discoid with flat or slightly convex valves.

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