Contributor: Jen Beals - December 2011
Length Range: 36-169 µm
Width Range: headpole 6.5-12; footpole 3-6.5 µm
Striae in 10 µm: 12-20
Frustules are heteropolar in both valve and girdle view. Valves are mildly arcuate. The headpole has two apices, with the ventral apex slightly more pronounced. The footpole is slightly swollen. Small spines are present on the margin of the valve face with one large spine present on the ventral apex of the headpole. There are short raphe branches at the apices originating in the mantle on the proximal end and hooking into the valve face on the distal ends. Raphe branches terminate internally in helictoglossae. There is one rimoportula at each apex of the valve on the mantle (rarely discernible in LM). Striae continue from the valve face onto the valve mantle and are punctate and parallel, becoming slightly radiate at the apices. There is a slight break in the striae originating at the distal raphe ends and continuing along the ventral margin of the valve face. There are 30-37 areolae in 10 µm in each stria.
Size and striae ranges are from Kociolek et al. (1997).
Basionym: Actinella punctata
Author: F.W. Lewis 1864
Length Range: µm
Striae in 10 µm:
V. ACTINELLA PUNCTATA, n. sp., is the only species yet found. Frustules linear, arcuate, commonly in radiating, symmetrical clusters of from six to twelve individuals. " F. V. straight, slightly cuneate, narrowing gradually from the extremities towards the centre ; ends more or less truncate. V. arcuate with a well marked notched inflation at the free extremity, smaller (attached) end rounded, with terminal nodules and sharp convergent striae, and a row of marginal puncta." Habitat on the surface mud. Fig. 5, a, b and c. The idea first suggested by the singular irregularity of development in this diatom, is rather that of accidental deformity, than that of definitive and permanent character, and this view I was disposed to adopt, until after the discovery of specimens altogether identical, from another and distant locality. Like most of the Saco species, A. punctata enjoys a very extended range of variation in size, length, proportion, definition of striation and punctulation; in no case, however, has the distinctive peculiarity (the unequally notched inflation) been found absent. Indeed, so invariable is it that a few worn valves, in the mud, dredged from Wolfboro' inlet, (Lake Winnipisseogee), at least sixty miles distant from the Saco pond, present this same special character; and recent gatherings, after a period of three years, show no difference in this respect. The peculiar notched inflation, which appears to be a fixed character of this diatom, equally with the tendency to punctate arrangement observable in several species in the gathering, possesses a certain significance, as showing how strongly a dominant Nitzschoid (Synedroid) leaning exists throughout the group. I have before alluded to the disposition to marginal punctulation evident in A. punctata, Tabellaria flocculosa, and one or two doubtful smaller forms in the Saco mud, as affording probable illustration of a sympathetic intrinsic force, tending towards the Nitzschoid type. In A. punctata there would seem be, as it were, a double exercise of this attractive force, conducting, not an allied form, but one only remotely connected with it, towards the same type. The antetype in the present case would appear to be Eunotia, between which and the Synedroid genera this anomalous form constitutes an intermediate or comprehensive link.
Kociolek, J.P., Rhode, K. and Williams, D.M. (1997). Taxonomy, ultrastructure and biogeography of the Actinella punctata species complex (Bacillariophyta: Eunotiaceae). Nova Hedwigia, Microalgae: Aspects of Diversity and Systematics 65: 177-194.
Lewis, F.W. (1864). On some new and singular intermediate forms of Diatomaceae. Proceedings of the Academy of Natural Sciences of Philadelphia 15:336-346.