• Category
  • Length Range
    12-15 µm
  • Width Range
    3.4-4.9 µm
  • Striae in 10 µm
  • Reported As
    Navicula biconica (Patrick and Reimer 1966, pg. 469, pl. 44, Fig. 8)



Valves are lanceolate with bluntly rounded to subrostrate apices. The sternum is distinctly silicified, with a conspicuous, rectangular central nodule. The central area is absent. Striae are often more readily resolved in the center, becoming more dense, to unresolvable near the apices. Striae are parallel throughout. Areolae are not resolvable in LM. Valves may be so lightly silicified that only the sternum is visible.

Hustedt (1949) described N. molestiformis from a single specimen in Africa. Not surprisingly, striae of specimens in US populations have a larger range (24-34) than the number of striae in the original description (28-30 in 10 µm).

Note that C. molestiformis (Hustedt) Lange-Bertalot in Rumrich et al. 2000 is a later isonym of C. molestiformis (Hustedt) Mayama 1999.

Also, Navicula biconica Patrick is considered to be conspecific with C. molestiformis (Hustedt) Mayama (Potapova 2013). The original description and line drawing illustration of N. biconica misrepresented the size of the type material, yet the name N. biconica was frequently used in surveys. We confirmed that many of the N. biconica records at the Academy of Natural Sciences of Drexel University included C. submolesta.


Craticula molestiformis is one of the most commonly reported Craticula in river surveys, and has been recorded from throughout the United States including Hawaii. Though it is often reported in low numbers, the highest densities of the species have been found to occur in Nebraska.

Original Description

Schalen dünnwandig, elliptisch-lanzettlich mit sehr kurz und stumpt geschnäbelten Enden, um 17 µ lang, etwa 5 µ breit. Raphe fadenförmig, mit auffallend entfernt gestellten Zentralporen. Axialarea sehr schmal linear, Zentralarea fehlt. Transapikalstreifen durchweg senkrecht zur Mittellinie, im mittleren Teil der Schale 28-30 in 10 µ, gegen die Enden zarter werdend und enger gestellt, bis etwa 35 in 10 µ (Taf. 5, Fig. 9).

Eduardsee, sehr selten im Plankton in der Bucht von Kamande.

Unterscheidet sich von der vorhergehenden Art sowie von der damit verwandten Navicula molesta Krasske durch die wesenlich zartere Struktur und die entfernt gestellten Zentralporen.

  • Basionym
    Navicula molestiformis
  • Author
    Hust. 1949
  • Length Range
    7 µm
  • Width
    5 µm

Original Images

Molestiformis Des
Navicula molestiformis orig illus
Navicula molestiformis

EMAP Assessment

EMAP Distribution

Craticula Molestiformis   Hustedt   Lange  Bertalot 10
Map 10

Response Plots

Craticula Molestiformis   Hustedt   Lange  Bertalot

Cite This Page

Vaccarino, M, and LaLiberte, G. (2015). Craticula molestiformis. In Diatoms of North America. Retrieved June 24, 2018, from https://diatoms.org/species/craticula_molestiformis


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Craticula molestiformis 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.