Asterolampra vulgaris
From Frustule
Additional Remarks
- Remarks by Greville (1862):
- The most variable of all the Barbadoes Asterolamprae, not only in the number of rays, which range from six to twenty, and in the cellulate or non-cellulate umbilicus, but also in the characters derived from the segments. Discs from the extreme ends of the series, might readily be taken for distinct species; and yet it is exceedingly difficult to define the varieties. In drawing up the specific character, I have been unable to discover any part upon which I could place the least dependence, except the lateral cellules of the segments of the valve, which seem always to project more or less beyond the rest; and it is mainly to modifications of the same part, that I have had recourse in separating the varieties. There is no rule with regard to the amount of space in the valve occupied by the segments themselves. It is very frequently half the radius, often considerably less; and in some of the large varieties, where the centre is occupied with numerous cellules, the radius is generally divided into three nearly equal parts, viz., the segments, the hyaline area transversed by the umbilical lines, and the central group of cellules (figs. 23, 24). With regard to the elongated cellules of the segments, they differ greatly in length in the more remarkable varieties, as do also the lateral cellules, compared with the intermediate ones. The lateral cellules are sometimes quite straight; at others, slightly curved inwards towards the apex. They are generally so far separated as to admit of the passage of the rays between them to the margin of the valve; but the passage is sometimes partially interrupted, in consequence of the cellules being occasionally somewhat enlarged toward their apices, and touching each other at that point (fig. 22). Very rarely the lateral cellules are united throughout their whole length, and, consequently, the narrow portion of the ray is rendered obsolete (fig. 21). Perhaps the most extreme variety is one which I at first considered distinct, and named A. splendida (fig. 25); and even now, I am not quite satisfied about its true position. The extraordinary ength of the cellules, which constitute nearly the whole substance of the segments distinguish the few imperfect valves I have seen. But the cellules of the segments in this species are so exceedingly variable, that a mere difference in length, however great, will scarcely, I fear, afford a satisfactory diagnosis. Of this protean diatom I have examined a multitude of specimens, besides taking notes of about sixty valves, in order to ascertain as far as possible the range of variation.
- Remarks by Gombos (1980):
- According to Greville this is the most variable of the Asterolampra species which he encountered in his study of the genus in Barbados. He described five varieties (varieties a through e) which are differentiated on the basis of inclination, length and distance between the lateral areolae or the number of rays, All the varieties taked together form a continuous series whose two end members, if taken separately, could be considered distinct species (Greville 1862, p. 48). The unifying characteristics of the varieties is the extension of the lateral areolae of the inner margin of the areolated segments beyond the others. Except for Asterolampra brightwelliana (see above), all forms which possess this feature should be considered as Asterolampra vulgaris sensu lato.
Useful References
- Greville, R. K., 1862. On the Asterolamprae of the Barbadoes deposit. Microscopical Society of London, Transactions, London, England, n. s., vol. 10, pp. 47, 48.
