Craticula molestiformis

(Hust.) Mayama 1999      Category: Symmetrical biraphid
BASIONYM: Navicula molestiformis Hust. 1949

REPORTED AS: Navicula biconica (Patrick and Reimer 1966, pg. 469, pl. 44, Fig. 8) 

Craticula johnstoniae


Craticula pampeana

LM scalebar = 10 µm = 80 pixels.


Contributor: Melissa Vaccarino | Gina LaLiberte - May 2015
Length Range: 12-15 µm
Width Range: 3.4-4.9 µm
Striae in 10 µm: 24-34


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.

Original Description

Basionym: Navicula molestiformis
Author: Hust. 1949
Length Range: 7 µm
Width Range: 5 µm
Striae in 10 µm:

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.

Original Images

Cite This Page:
Vaccarino, M., and LaLiberte, G. (2015). Craticula molestiformis. In Diatoms of the United States. Retrieved April 23, 2018, from

Species: Craticula molestiformis

Contributor: Melissa Vaccarino | Gina LaLiberte

Reviewer: Kalina Manoylov


Hustedt, F. (1949). Süsswasser-Diatomeen aus dem Albert-Nationalpark in Belgisch-Kongo. Exploration du Parc National Albert, Mission H. Damas (1935-1936), Institut des Parcs Nationaux du Congo Belge, Bruxelles 8:199 pp., 16 pls.

Mayama, S. (1999). Taxonomic revisions to the differentiating diatom groups for water quality evaluation and some comments for taxa with new designations. Diatom, the Japanese Journal of Diatomology 15: 1-9.

Potapova, M. (2013). The types of 22 Navicula (Bacillariophyta) species described by Ruth Patrick. Proceedings of the Academy of Natural Sciences of Philadelphia 162: 1-23.

Rumrich, U., Lange-Bertalot, H. and Rumrich, M. (2000). Diatoms of the Andes. From Venezuela to Patagonia/Tierra del Fuego and two additional contributions. Lange-Bertalot, H. (ed.), Iconographia Diatomologica. Annotated Diatom Micrographs. Vol. 9. Phytogeography-Diversity-Taxonomy. Koeltz Scientific Books, Königstein, Germany, 9:673 pp.

Links & ID's

Index Nominum Algarum (INA)

Original INA
Transfer INA

California Academy of Sciences (CAS)

Craticula molestiformis CAS

NCBI Genbank Taxonomy

Craticula molestiformis NCBI

North American Diatom Ecological Database (NADED)

NADED ID: 21015

Autecology Discussion

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.

EMAP Assessment

The Environmental Protection Agency (EPA) western Environmental Monitoring and Assessment Program (EMAP) study was completed during the years 2000-2004 (see citations at bottom of this page). Over 1200 streams and rivers in 12 western states (Arizona, California, Colorado, Idaho, Montana, Nevada, North Dakota, Oregon, South Dakota, Utah, Washington and Wyoming) were selected for sampling based on a stratified randomized design. This type of design insures that ecological resources are sampled in proportion to their actual geographical presence. Stratified randomized design also allows for estimates of stream length with a known confidence in several “condition classes” (good or least-disturbed, intermediately-disturbed, and poor or most-disturbed) for biotic condition, chemistry and habitat.

EMAP Distribution

Craticula molestiformis

EMAP Response Plots

Craticula molestiformis

EMAP citations

Results are published in:

Johnson, T., Hermann, K., Spaulding, S., Beyea, B., Theel, C., Sada, R., Bollman, W., Bowman, J., Larsen, A., Vining, K., Ostermiller, J., Petersen, D. Hargett, E. and Zumberge, J. (2009). An ecological assessment of USEPA Region 8 streams and rivers. U.S. Environmental Protection Agency Region 8 Report, 178 p.

Stoddard, J. L., Peck, D. V., Olsen, A. R., Larsen, D. P., Van Sickle, J., Hawkins, C. P., Hughes, R. M., Whittier, T. R., Lomnicky, G. A., Herlihy, A. T., Kaufman, P. R., Peterson, S. A., Ringold, P. L., Paulsen, S. G., and Blair, R. (2005). Environmental Monitoring and Assessment Program (EMAP) western streams and rivers statistical summary. U.S. Environmental Protection Agency Report 620/R-05/006, 1,762 p.

Stoddard, J. L., Peck, D. V., Paulsen, S. G., Van Sickle, J., Hawkins, C. P., Herlihy, A. T., Hughes, R. M., Kaufman, P. R., Larsen, D. P., Lomnicky, G. A., Olsen, A. R., Peterson, S. A., Ringold, P. L., and Whittier, T. R. (2005). An ecological assessment of western streams and rivers. U.S. Environmental Protection Agency Report 620/R-05/005, 49 p.