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Girdle view: Close set chains; cells straight; valves flat. Bands coarsely ribbed (LM).

Valve view: Valve ribs visible with LM. Internal part of process a low tube with thickened rim (LM).

Dactyliosolen tenuijunctus (Manguin) Hasle (Table 37) Basionym: Rhizosolenia tenuijuncta Manguin.

References: Manguin, 1957, p. 118, Plate 2, Fig. 15; Manguin, 1960, p. 270, Figs. 76 and 77; Hasle, 1975, p. 122, Figs. 114-120; Priddle & Fryxell, 1985, p. 60. Cells straight, slightly curved, or undulated; valve face flat(?). Bands delicately ribbed. Internal part of process tubular (LM).

B. Band ends in a straight line.

Dactyliosolen blavyanus (H. Peragallo) Hasle (Plate 32, Table 37) Basionym: Guinardia blavyana H. Peragallo.

References: Peragallo, 1892, p. 107, Plate 1, Figs. 1 and 2; Hustedt, 1930, p. 564, Fig. 323; Hasle, 1975, p. 121, Figs. 101-108 and 113; von Stosch, 1986, p. 317, Fig. 12. Girdle view: Close set chains; cells straight; valve surface flat with a marginal indentation at the process. Bands delicately ribbed and discernible with LM.

Valve view: Faint valve ribs (LM). Process marginal; internal part tubular (LM).

Dactyliosolen fragilissimus (Bergon) Hasle comb. nov. (Plate 31, Table 37) Basionym: Rhizosolenia fragilissima Bergon.

References: Bergon, 1903, p. 49, Plate 1, Figs. 9 and 10; Hustedt, 1930, p. 571, Fig. 324; Cupp, 1943, p. 80, Fig. 41; Drebes, 1974, p. 48, Figs. 34b and 34c; Hasle, 1975, p. 114, Figs. 61, 62, and 74-78; Sundstrbm, 1986, p. 103, Figs. 268 and 269; Takano, 1990, pp. 262-263. Girdle view: Cells straight and united in loose chains by the central part of valve surface. Bands difficult to see with LM; rectangular poroid areolae (EM). Valves weakly convex. External process tube narrow, slightly curved fitting into a depression (pocket) in adjacent cell, and visible with LM as an indentation near the tube.

Valve view: Valve structure too delicate to be resolved with LM. Internal part of process lacking (?).

Dactyliosolen phuketensis (Sundstrom) Hasle comb. nov. (Plate 31, Table 37)

Basionym: Rhizosolenia phuketensis Sundstrom.

References: Sundstrom, 1980, p. 579, Figs. 1 and 3; von Stosch, 1986, p. 323, Figs. 15-17; Sundstrom, 1986, p. 103, Figs. 270 and 271.

Cells curved; in close set curved or spiraling chains. Bands visible with LM; rectangular poroid areolae (TEM). Internal part lacking (?).

Distribution:

D. tenuijunctus—southern cold water region.

D. blavyanus—warm water region to temperate including the Oslofjord, southern Norway in summer.

D. phuketensis—warm water region to temperate including North Sea and the Skagerrak (Sundstrom, 1986). D. fragilissimus—cosmopolitan (?).

D. antarcticus—cosmopolitan (?), especially important in the southern cold water region. How to identify: The species may be identified in girdle view in water mounts, in a medium of a higher refractive index, or possibly as dried material mounted in air. Material cleaned of organic matter and mounted in a medium of a high refractive index is needed in order to see the valve structure and the shape of the internal part of the process. Remarks: Dactyliosolen blavyanus differs from the other species of the genus by being the only one known to form (endogenous) resting spores and by having the protoplast concentrated to the middle of the cell (von Stosch, 1986). Guinardia delicatula, D. fragilissimus, Leptocylindrus danicus, and Cerataulina pelagica often appear together as do G. striata and G. phuketensis.

They are distinguished by: Shape of valve.

The Dresence/absence. shaoe. and location of orocess. Sha

Bands, shape, ends in straight/oblique line. Suborder Biddulphiineae

Family Hemiaulaceae Jouse, Kisselev, & Poretsky 1949

The four recent planktonic genera dealt with here were all placed in this family by Simonsen (1979) as well as by Round et al. (1990). In Round et al. (1990), Hemiaulaceae was placed in the new order Hemiaulales Round &c Crawford. Glezer et al. (1988) placed Eucampia together with Odontella and Biddulphia in Biddulphiaceae Kiitzing.

Terminology specific to Hemiaulaceae

Aperture—space between valves of adjacent cells in chains.

Elevation—raised portion of valve wall, not projecting laterally beyond valve margin, may bear some special structure; otherwise with the same structure as the valve.

Horn—long, narrow elevation.

Ocellus—plate of silica, pierced by closely packed holes, normally with a thickened structureless rim. Costate ocellus—similar to an ocellus or pseudocellus (see Eupodiscaceae) but with siliceous ribs between rows of pores.

Common morphological characters:

Close set chains formed by apposition of tips of elevations. Bipolar symmetry. Bipolar elevations.

Apertures between cells in colonies formed by elevations. A single labiate process. Poroid areolae.

Numerous small disc-like chloroplasts.

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