la. Valve outline varying according to cell size: larger cells linearly elliptical, median cells broadly elliptical with broadly rostrate ends, smallest cells lanceolate N. pelagica Takano lb. Valve outline of all cell sizes: linear, inflated at the center and less so at apices N. indica19 (F. J. R. Taylor) Tanimura
N. indica—warm water region to temperate (?)—Indian Ocean, Gulf of Mexico, Gulf of California, and Central and North Pacific. N. pelagica—warm water region to temperate (?)—Japan, coasts of Texas and Florida (Round et al., 1990), and Pacific Ocean off Mexico (Hernändez-Becerril, 1990). Remarks: A further distinctive feature of Neodelphineis compared to Delphineis is the presence of pointed, raised single spines located on the interstriae on the edge of the valve face (SEM).The light micrographs of Synedra indica in Simonsen (1974, Plate 23, Figs. 9-18) illustrate the invariability of the valve outline of N. indica (11-37 /u.m long, Simonsen 1974, Figs. 9-14) and a part of the variability of the valve outline of N. pelagica (ca. 15-24 /tm long; Simonsen 1974, Figs. 15-18).
Genus Rhaphoneis Ehrenberg 1844
Lectotype: Rhaphoneis amphiceros (Ehrenberg) Ehrenberg (vide Boyer, 1927, p. 190).
" Basionym: Synedra indica F. J. R. Taylor.
PLATE 52 Neodelphineis indica: valves showing outline, striation, apical pores and labiate processes. Scale bar = 10 p.m. Rhaphoneis amphiceros: valves, size variation. Striation, sternum, apical pore fields, and labiate processes. After Hustedt (1959). Scale bar = 10 /um. Toxarium undulatum: (a) valve outline. Scale bar = 100 pm; (b) central part of valve, showing structure. Scale bar = 10 /im. After Cupp (1943).
The lectotype seems to be the only commonly recorded recent species left in this genus.
Rbaphoneis amphiceros (Ehrenberg) Ehrenberg (Plate 52) Basionym: Cocconeis amphiceros Ehrenberg.
References: Ehrenberg, 1841b, p. 206; Ehrenberg, 1844a, pp. 74 and 87; Hustedt, 1959, p. 174, Fig. 680; Hendey, 1964, p. 154, Plate 26, Figs. 1-4; Drebes, 1974, p. 101, Fig. 83; Round et al., 1990, p. 406. Cells solitary and often attached to sand grains. Valve outline broadly elliptical or lanceolate with produced almost capitate apices to subcircular. Striae parallel or radiating. Sternum narrow and lanceolate. Small and distinct (LM) apical pore fields. Chloroplasts small and numerous. Morphometric data: Apical axis, 20-100 /xm; transapical axis, 1825 /im, six or seven striae in 10 ¡x.m. Distribution: Probably cosmopolitan.
How to identify: Diatoms belonging to Rhaphoneidaceae can only be identified in valve view. The most coarsely silicified specimens may be identified in water mounts. Examination of cleaned valves mounted in a medium of a high refractive index is recommended.
Toxarium undulatum Bailey and T. hennedyanum Grunow are, at present, probably the only species in this family (Round et al., 1990). They are not typical plankton forms although T. hennedyanum was characterized as a "neritic plankton species" (Hendey 1964, p. 164). Toxarium undulatum was first found "attached in considerable numbers to Sargassum vulgare, in Narragansett Bay" (Bailey, 1854, p. 15), and Bailey's two other records of T. undulatum were also from Sargassum.
Genus Toxarium J. W. Bailey 1854 (Plate 52)
Type: Toxarium undulatum J. W. Bailey.
Synonym: Synedra undulata (J. W. Bailey) Gregory.
References: Bailey, 1854, p. 15, Figs. 24 and 25; Gregory, 1857, pp. 531-533, Plate 14, Figs. 107 and 108; Van Heurck, 1880-1885, Plate
42, Fig. 3; Hustedt, 1959, pp. 222-224, Figs. 713 and 714; Round et al.,
Needle like in valve and girdle views.
Valves slightly expanded at both apices and at the center.
No distinct sternum.
Areolae scattered over valve face.
Toxarium undulatum has undulated valve margins; T. henttedyanum (Gregory) Grunow in Van Heurck (syn. Synedra hennedyana Gregory) has smooth valve margins. Morphometric data:
T. henttedyanum—apical axis, 300-900 /¿m; transapical axis, 6-8 (jlm in valve center, 5-6 fim at the apices, and 2 ¡xm in between; 9-11 striae in 10 ¿im (Hustedt, 1959).
T. undulatum—apical axis, up to 600 (jlm; 10-18 striae in 10 ¿im near apices (Hendey, 1964). Distribution: Common, especially in tropical/subtropical waters (Round et al., 1990), but also occasionally in temperate waters. How to identify: These two species are coarsely structured and may be identified in valve view in water mounts.
Family Thalassionemataceae Round 1990
In contrast to the other araphid families, Thalassionemataceae is exclusively marine and planktonic.
Cells solitary or in colonies of various types.
Cells needle shaped, often long, twisted, sometimes curved and expanded in the middle and at the apices.
Sternum usually wide and often varying in width along the cell length.
Areolae loculate with internal foramina and external vela (SEM).
Areolae circular to elongate transapically.
One labiate process at each end.
Apical spine(s) usually present at one or both ends.
Apical fields absent.
Marginal spines present or absent.
Numerous small chloroplasts scattered throughout the cell.
Was this article helpful?