Aulacoseira tenella

Diagnosis. Trichomata brevia, rigida, usque ad 4-, saepe 2-cellularia, pseudosulcis satis profundis. Cellulae cylindraceae, solum proxime pseudosulcos coarctatae, sulcis destitutae, interdum tamen medio lenissime constrictae, discis planis inter se dense connatae. Membrana lateralis striata, striis cum axe pervalvari angulos formantibus inter —34 et + 47 gradus varios, plerosque aut 0 aut 17—18 aut 21—22 graduum. Striae 0.8—1.5 μ longae, 23—26 pro 10 μ, saepe regulariter, raro irregulariter punctatae, punctis orbicularibus vel suboblongis, 22—27 pro 10 μ. Discus spinis parvulis marginalibus interstrialibus instructus, intra marginem punctis 22—27 pro 10 μ in seriebus subtangentialibus 23—26 pro 10 μ dispositis ornatus. Latitudo cellularum 5.1—5.9 μ, longitudo 3—4.2 μ; altitudo semicellularum 1.4— 2.2 μ, latitudine 2.5—4.2 a parte minor. Hab. subfossilis in lacu Store Gribsø Selandiae septentrionalis Daniae. Finer structures. The diameter of the pores on discus is 0.07—0.24 μ, usually 0.15—0.2 μ. The pores of the girdles measured 0.15—0.28 μ in diameter. At the bottom of the pores lie sieve plates, the pores of which measure only 30—40 mμ in diameter. The spines at the margin of discus are strongly compressed and triangular with concave sides, 0.2—0.35 μ long, and about 0.7 μ broad. Statistics. The filaments were usually two-celled, three-celled colonies were very rare, and only once was a four-celled filament observed. The samples contained a great many single cells, possibly due to the treatment with sulphuric acid. The cell length varied between 3 and 4.2 μ. The average amounted to 3.5 μ and the standard deviation to 0.3 μ (n = 36). The true value thus lies between 3.5 μ ± 3x0.3 μ or between 4.4 μ and 2.6 μ in 99.7 % of all cases. The height of the semicells ranged from 1.4—2.2 μ. The average was 1.7 μ and the standard deviation 0.17 μ (n = 72). The true value lies then between 1.7 μ ±3x0.17/4 or between 2.2 μ, and 1.2 μ in 99.7 % of all cases. The cell breadth varied between 5.1 and 5.9 μ. The average was 5.5 μ, and the standard deviation was 0.2 μ (n = 36). Consequently the true value lies between 5.5 μ ± 3x0.2 μ or between 6.1 μ and 4.9 μ in 99.7 % of all cases. The number of striae per 10 μ was 23—26, the average 25, and the standard deviation 1 (n = 36). The true value thus lies between 25± 3x1 or between 28 and 22 striae per 10 μ in 99.7 % of all cases. The puncta were present in a number of 22—27 per 10 μ. The average amounted to 25, and the standard deviation was 1.4 (n = 36). The true value consequently lies between 25 ±3x1.4 or between 29 and 21 puncta per 10 μ in 99.7 % of all cases. The length of the striae was 0.8—1.5 μ, the average 1.1 μ, and the standard deviation 0.17 μ (n = 72). The true value is lying between l.l μ ± 3x0.17 μ or between 1.6 μ and 0.6 μ in 99.7 % of all cases. The ratio between breadth and height was measured as 2.5—4.2, the average being 3.2. The standard deviation was computed to be 0.3 (n = 72), and the true value thus lies between 3.2 ± 3x0.3 or between 4.1 and 2.3 in 99.7 % of all cases. The angles between the striation and the pervalvar axis were measured in 41 cells. In this material 27 different angles were found, ranging from — 34° to + 47° of arc. It should be emphazised, however, that although the drawing was performed at a magnification of 4800, it is very difficult to draw lines exactly through the delicate puncta of this small species. Cells in which all striae demonstrate the very same inclination (18°) are rare if altogether existing, the striation of the under side usually being too indistinct for depiction. In general 2—4 angles were measured on the individual cell, e.g. — 28°, 0°, and 22°, or 0° and 18°, or 18° and 22°. A total of 106 angles was measured. The most common angles met with were 0°, occurring in 17%, 17°—18° in 19%, and 21°—22° in 19% of the total number of angles measured. The groups of 17°—18° and 21°—22° should possibly be united to one group of about 20° owing to the inevitable errors of measurement. Among the more rarely occurring angles — 28° (3.8%), — 20° to — 22° (5.6%), and 9 or 10° (7.5%) should be mentioned.

• Basionym
  Melosira tenella
• Author
  Nygaard 1956
• Length Range
  5.1-5.9 µm
• Width
  1.4-2.2 µm
• Striae in 10µm
  23-26