• Category
  • Length Range
    8.5-10.4 µm
  • Width Range
    4.4-5.2 µm
  • Striae in 10 µm
  • Synonyms
    Achnanthes hintzii Lange-Bert. and Krammer



Valves are elliptic. Raphe valve has a narrow linear axial area and a transversely rectangular central area. The raphe is filiform and straight with slightly expanded, almost straight or very slightly deflected external distal and proximal ends. Internal proximal raphe ends are deflected to opposite sides. Internal distal ends terminate in small helictoglossae. The rapheless valve has a narrow linear axial area and a transversely rectangular central area that may be symmetric, or slightly asymmetric. Striae are uniseriate. Areolae are isodiametric and number 25 in 10 μm. There are 5-7 areolae in each central stria.

Note that specimens from the type material from Europe have slightly larger valves (about 6 μm wide) and more distinctly asymmetric central area on rapheless valve than specimens from the U.S. This species is, however, extremely rare in the type material and at present it is not possible to determine whether specimens from Europe and North America belong to the same species.

Note that this taxon was originally described as Cocconeis semiaperta Hustedt (1945, Arch. Hydrobiol. 40: 905, pl. XXXIX: figs. 1-3.) Achnanthes hintzii Lange-Bertalot and Krammer (1989, Biblioth. Diatomol. 18: 64) was a new name of the type.


Original Description

Cocconeis semiaperta n. sp. - Schalen breit elliptisch, um 10 µ lang, etwa 6 µ breit. Raphenschale mit gerader, fadenförmiger Raphe, Axialarea sehr eng, Zentralarea einseitig bis fast an den Schalenrand erweitert. Transapikalstreifen durchweg radial, etwa 25 in 10 µ zart punktiert, Punkte in unregelmäßig welligen Längslinien, die annähernd in derselben Entfernung stehen wie die Transapikalstreifen. Raphenlose Schalen mit sehr schmal lanzettlicher Axialarea, Zentralarea einseitig bis an den Schalenrand er- weitert, Struktur der Zellwand wie an der Raphenschale.Taf. XXXIX Abb. 1-3. Plitvicer Seengebiet, sehr selten in einem Wasserfall und an litoraler Chara. - Besonders charakteristisch durch die Form der Zentralarea und mit keiner anderen Art zu verwechseln.

  • Basionym
    Cocconeis semiaperta
  • Author
    Hust. 1945
  • Length Range
    10 µm
  • Width
    6 µm
  • Striae in 10µm

Original Images

Ps Semiapertum  Orig Ill
Ps Semiapertum  Orig Descr

Cite This Page

Potapova, M. (2011). Psammothidium semiapertum. In Diatoms of North America. Retrieved May 20, 2024, from https://diatoms.org/species/psammothidium_semiapertum


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Psammothidium semiapertum from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:

ELEVATION = stream reach elevation (meters)
STRAHLER = distribution plot of the Strahler Stream Order
SLOPE = stream reach gradient (degrees)
W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.
PHSTVL = pH measured in a sealed syringe sample (pH units)
log_COND = log concentration of specific conductivity (µS/cm)
log_PTL = log concentration of total phosphorus (µg/L)
log_NO3 = log concentration of nitrate (µeq/L)
log_DOC = log concentration of dissolved organic carbon (mg/L)
log_SIO2 = log concentration of silicon (mg/L)
log_NA = log concentration of sodium (µeq/L)
log_HCO3 = log concentration of the bicarbonate ion (µeq/L)
EMBED = percent of the stream substrate that is embedded by sand and fine sediment
log_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).
DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.