Sellaphora hohnii

Sellaphora hohnii Potapova & Ponader, sp. nov. TYPE: USA. Florida: Silver Springs, 20 September 1955, J.L. Yount. (Holotype: ANSP GC 44484). Fig. 3A. Synonym: Navicula cristula Hohn excl. Typus, Trans. Am. Micr. Soc. 53(2): Fig. 2/6, 1961. Valvae ellipticae, apicibus subrostratis, 28--47 µm longae, 8.9--9.8 µm latae. Area axialis recta. Sulci utroque fissurae raphis latere, ca. 1 µm lati, conopeis non porosis. Sulci et conopea area centralis interruptis. Area centralis transverse rectangulata, versus marginem dilatata. Striae uniseriatae, radiatae, ad apices parallelae vel convergentes, 20-23 in 10 µm. Areolae parvae circulares, 53-55 in 10 µm. Raphe recta, extremis centralis dilatatis, fissurae terminales deflectis ad latus secundarium valvae. Valves are elliptical, with subrostrate apices, 28-47 µm long, 8.9-9.8 µm wide (Fig. 3). The axial area is straight, formed by grooves, one at each side of the raphe. Grooves are approximately 1 µm wide and are covered externally by non-porous conopeum (Fig. 3E, F, H). Grooves and conopea are interrupted by the central area, which is transversely rectangular or bow-tie-shaped, and bordered by striae of an irregular length. The striae are uniseriate, radiate throughout most of the valve, but parallel or convergent near the apices, 20-23 in 10 µm near the valve ends, the striae are interrupted and internally form "polar bars" (Fig. 3G), which are also visible on LM photographs (Figs 3A-D). The areolae are small, rounded, approximately 53-55 in 10 µm. As in other species of Sellaphora they are occluded internally by hymens (Fig. 3G). The raphe is straight, with expanded central endings, and terminal fissures curved to the secondary side of the valve (Fig. 3F). This species closely resembles S. californica Potapova (Potapova and Charles, 2004), but differs from it by having wider and less drawn-out apices. In quantitative terms, this shape difference is partly described by the ratio of the pole width to maximum valve width, which is ca. 1: 1.8 in S. hohnii, and ca. 1: 2.5 in S. californica. S. hohnii is also similar to S. tibia Antoniades & Hamilton (Antoniades et al., 2008) which has the same conopeum and raphe structure, but S. tibia has a more linear valve form and lower areolae density. Etymology: Hohn (1961) found this species in Silver Springs, Florida and identified it as Navicula geitleri Guermeur & Manguin. The name “N. geitleri Guermeur & Manguin” was, however, illegitimate because of the earlier N. geitleri Hustedt. Hohn, therefore, established N. cristula as a replacement name for N. geitleri Guermeur & Manguin. Examination of the drawing of “N. geitleri” in Guermeur and Mangiun (1953) shows that this diatom, described from Europe, is different morphologically from the Sellaphora found in Silver Springs. Since the type of N. cristula is a diatom described by Guermeur & Manguin, and this species is different from the Sellaphora from Silver Springs, we describe the latter as a new species and name it in honor of Dr. Matthew H. Hohn.

• Author
  Potapova and Ponader 2008
• Length Range
  28-47 µm
• Width
  8.9-9.8 µm
• Striae in 10µm
  20-23