Synedropsis Hyperborea

1 a. Cells in girdle view narrow with straight parallel sides and greatly expanded triangular foot pole; foot pole greatly widened and rounded in valve view, one or two chloroplasts in foot pole only

A. glacialis (Castracane) Round lb. Cells in girdle view broad at foot pole, then suddenly constricted, then gradually widening again to the middle, then tapering toward head pole, two lobed, chloroplasts A. kariana17 (Grunow) Round

Morphometric data: A. glacialis—apical axis, 30-150 jum; length of expanded part, 10-23 /im (ca. one-fourth of total length); transapical axis of expanded part, 8-12 /urn; 28-34 transapical striae in 10 p.m. A. kariana—Apical axis, 16-68 /zm; transapical axis of foot pole, ca. 3 ¡xm; at constriction, ca. 1 /¿m; median part, ca. 3-4 fxm; head pole, ca. 0.5 ixm (Körner, 1970).


A. glacialis—cosmopolitan, sometimes abundant in plankton in cold to temperate coastal waters.

A. kariana—northern cold water region to temperate (?). How to identify: Whole cells in girdle view show sufficient details that the two species are distinguishable.

Remarks: Asterionella socialis Lewin & Norris (Lewin &c Norris, 1970, p. 145), which was described from the surf zone in the State of Washington, should also be transferred to Asterionellopsis (Round et al., 1990, p. 392). Asterionellopsis glacialis cultured for some time regularly looses the narrow part of the Cells and occurs as triangular or almost circular cells (G. Hasle and E. Syvertsen, personal observations; Körner, 1970, Figs. 119-122). Whereas both poles of A. glacialis have apical slit fields (Körner, 1970, Figs. 108-110; Hasle, 1973c, Figs. 22-25; Takano 1983, p. 27; Round et al., 1990, p. 393; Takano, 1990, p. 304), the broad foot pole of A. kariana carries pores and the narrow head pole slits (Körner, 1970, Fig. 126; Takano, 1990, pp. 306 and 307) and A. socialis seems to be like A. kariana in this respect (Lewin & Norris, 1970, Fig. 15).

Genus Bleakeleya Round in Round et al., 1990

Type: Bleakeleya notata (Grunow) Round in Round et al.

Monospecific genus.

" Basionym: Asterionella kariana Grunow in Cleve 8c Grunow

Bleakeleya notata (Grunow) Round in Round et al. (Plate 50) Basionym: Asterionella bleakeleyi var. notata Grunow. References: Grunow, 1867, p. 2; Hustedt, 1959, p. 254, Fig. 733; Round et al., 1990, p. 394.

Cells linear in girdle and valve views with dissimilar ends. Cells united by valve faces of expanded foot poles, in flat or twisted chains. Head pole rounded in valve view. Foot pole in valve view slightly inflated with a more or less angular or rounded outline, crossed by a transverse bar from which a narrow sternum rises. Basal part of foot pole with smaller areolae in radiating striae. Chloroplasts—numerous small granules scattered throughout the cell. Morphometric data: Apical axis, 50-170 /xm; transapical axis of foot pole, 4-10 /¿,m; of head pole, 1.6-3 fim; 30-36 transapical striae in 10 fxm (Körner, 1970).

Distribution: Warm water region.

How to identify: The shape of the colonies characterizes this species. Identification based on single cells or valves requires cleaned material mounted in a medium of a high refractive index.

Genus Striatella C. A. Agardh 1832

Lectotype: Striatella unipunctata (Lyngbye) C. A. Agardh (vide Ehrenberg, 1838, pp. 202 and 230).

Monospecific genus (as proposed by Round et al., 1990, p. 432).

Striatella unipunctata (Lyngbye) C. A. Agardh (Plate 50) Basionym: Fragilaria unipunctata Lyngbye.

References: Lyngbye, 1819, p. 183, Plate 62, Fig. G; Agardh, 1832, p. 61; Cupp, 1943, p. 173, Fig. 122; Hustedt, 1959, p. 32, Fig. 560; Hendey, 1964, p. 161, Plate 26, Figs. 17 and 18. Girdle view: Tabular with corners appearing as being cut off. Cells united to form ribbons or zigzag chains. Numerous open bands with narrow septa. Chloroplasts granular to oblong and radially arranged. Valve view: Lanceolate with distinct apical pore fields, slightly sunk in and surrounded by a rim (SEM), thus the impression of cut off corners when seen with LM. One labiate process at each pole. Valve areolae in three self-crossing line systems. Sternum narrow. Morphometric data: Apical axis, 35-125 fim; transapical axis, 6-20 /zm; 6-10 bands in 10 fxm; areolae in 18-25 oblique lines in 10 /am. Distribution: Temperate species (Cupp, 1943).

How to identify: Striatella unipunctata is most easily identified as whole cells in girdle view in water mounts.

Remarks: Tessella interrupta Ehrenberg and Hyalosira delicatula Kotzing, both listed as Striatella species by Hustedt (1959), have been transferred to Microtabella F. E. Round (Round et al., 1990).

Synedropsis Diatoms

Synedropsis hyperborea

Synedropsis HyperboreaSynedropsis Hyperborea

Adoneis pacifica

PLATE 51 Fragilaria striatula: (a) ribbon in broad girdle view; (b) valve view with striation and sternum. Scale bar = 20 fim. Synedropsis hyperborea: (a) stellate colony, with cells in girdle and valve views; (b) valves, size variation. Scale bars = 20 p.m. Adoneis pacifica: valve with areolation, apical pore fields and four labiate processes. After Andrews & Rivera (1987). Scale bar = 20 p,m. Delphineis surirella: valves, size variation. Sternum broadened apically, apical pores, and labiate processes. After Hustedt (1959). Scale bar = 20 p,m.

Fragilaria striatula Lyngbye (Plate 51)

References: Lyngbye, 1819, p. 183, Plate 63; Hustedt, 1959, p. 150, Fig. 663; Hasle 8c Syvertsen, 1981, Figs. 18-23. Girdle view: Rectangular cells close together in ribbons, numerous narrow bands. Chloroplasts large, two per cell.

Valve view: Valves variable in silicification and outline, the latter varying from broadly to narrowly elliptical, and the shape of apices from rounded to slightly attenuate to almost capitate. A narrow sternum, parallel striae, a labiate process at one valve pole, and apical pore fields at each pole discernible with LM. Morphometric data: Apical axis, 25-53 ju,m; transapical axis, 6-10 fim; 17-28 transapical striae in 10 jum.

Distribution: Fragilaria striatula is benthic and a common epiphyte on larger algae but was also reported as a "neritic plankton species" by Hendey (1964). It was described from the Faeroe Is, North Atlantic, and is often recorded from other parts of the North Atlantic and from the Arctic. Due to the shape of the chains it may be confused with Fragilariopsis spp. How to identify: Fragilaria striatula cannot be identified in girdle view and has to be examined in valve view as cleaned material mounted in a medium of a high refractive index.

Remarks: The typification of Fragilaria has been disputed. Williams 8c Round (1987) suggested that the genus name should be conserved for freshwater species. The marine F. striatula was placed into this genus by the author of the genus, and the type material has been examined with EM (Hasle 8c Syvertsen, 1981). Boyer (1927) designated the freshwater species F. pectinalis as the lectotype of Fragilaria. The identity of this species is obscure, however.

Genus Synedropsis Hasle, Medlin, 8c Syvertsen 1994

Type: Synedropsis hyperborea (Grunow) Hasle, Medlin, 8c Syvertsen.

Synedropsis hyperborea (Grunow) Hasle, Medlin, 8c Syvertsen (Plate 51) Basionym: Synedra hyperborea Grunow.

Synonyms: Synedra hyperborea var. flexuosa Grunow; Synedra hyperborea var. rostellata Grunow.

References: Grunow, 1884, p. 106, Plate 2, Figs. 4-6; Hustedt, 1959, p. 217, Fig. 709; Hasle et al., 1994, p. 249, Figs. 1-12, 17-21, 24-26, 31-38, 45-47, and 142a. Girdle view: Cells narrowly linear in stellate colonies. Valve view: Specimens of maximum length rostrate; smaller valves with shorter prolongations; smallest specimens almost lanceolate; some valves with irregular inflations and indentations. A labiate process at one valve apex, a narrow sternum, and transapical striae discernible with LM. Apical slit fields (EM).

Morphometric data: Apical axis, 13-96 /xm; transapical axis, 2.5-4 /xm; 25-27 transapical striae in 10 pim.

Distribution: Northern cold water region, described from the undersurface of ice but often encountered in the plankton and as an epiphyte on Melosira arctica.

How to identify: Synedropsis hyperborea can probably be identified as whole cells in water mounts in Arctic material; in critical cases examination of many specimens mounted in a medium of a high refractive index using phase or interference contrast is needed to secure positive identification. Remarks: The Synedropsis species are mainly living associated with sea ice, either attached to the ice itself or to the ice diatoms. The Arctic S. hyperborea and, probably more seldom, the Antarctic S. recta Hasle, Medlin, 8c Syvertsen and S. hyperboreoides Hasle, Syvertsen, 8c Medlin, are also found in the plankton close to the ice.

Family Rhaphoneidaceae Forti 1912

The habitat of the four genera dealt with here is shallow coastal water over sandy shores and mud and sand flats. They may be attached to sand grains or other particles [e.g., valves of other diatoms (Drebes, 1974)], but may be stirred up in turbulent water and thus become part of the plankton.

Characters common to Adoneis, Delphineis, Neodelphineis, and Rhaphoneis:

Cells solitary or in ribbons or zigzag or stellate colonies. Cells rectangular in girdle view.

Valve outline linearly elliptical to broadly lanceolate, sometimes with produced apices or central inflation. Large poroid areolae in uniseriate parallel or radiate striae. Apical pore fields or one or two apical pores (EM).

One labiate process at each apex (one genus, Adoneis, usually with labiate processes also near the center of each lateral margin).

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