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Diatoms of the United States is now known as Diatoms of North America.
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GENERA starting with "m"


Mastogloia 7

  1. Valves elliptic to lanceolate, with rounded to capitate ends
  2. Valvocopula with partecta
  3. Striae punctate

Symmetrical biraphid - The valves of Mastogloia are elliptic to elliptic-lanceolate or lanceolate, with rounded to capitate ends. The valvocopula (first girdle band) each possess complex silica chambers, called partecta, that function to secrete strands of mucilage. The raphe is straight or undulate. The axial area is narrow, with a slightly expanded central area. Living cells have two plastids. Mastogloia is primarily a marine genus. A few...


  1. Cells small
  2. Axial area thickened
  3. Raphe straight

Symmetrical biraphid - Frustules of Mayamaea are small. The axial area is thickened and contains a straight raphe. Sometimes the axial area is all that remains from an acid preparation. The striae are uniseriate. Mayamaea includes the former Navicula atomus and its affiliates. Mayamaea species are found in ephemeral habitats as well as waters high in nutrient waste. Mayamaea species may reach high abundance in some polluted habitats.

Melosira 4

  1. Valve wall uniform in structure, little external ornamentation
  2. Frustules lack costae, septae, and spines
  3. Frustules may form colonies

Centric - Melosira valves have little ornamentation. They lack distinctive features including costae, septae, and spines. Frustules form long colonies linked at the valve face. Melosira contains a small number of freshwater species. M. varians, one of the most common species of the genus grows in benthic habitats of eutrophic streams and lakes. Melosira also contains the species M. undulata, which grows in large, oliogotrophic...

Meridion 5

  1. Valve symmetry to the transverse axis variable
  2. Frustules linear to wedge-shaped in girdle view
  3. Frustules may be joined in colonies
  4. Costae present

Araphid - Valves of Meridion are variable in symmetry to the transverse axis; they are either strongly heteropolar or isopolar. The heteropolar species are clavate (club-shaped) in valve view and wedge-shaped in girdle view. Septae (attached to girdle elements) are present. An apical porefield is present at one end. Valves may have 1-2 rimoportulae. Cells are joined together to form fan-shaped colonies. Chloroplasts are multiple...

Microcostatus 1

  1. Central sternum prominent
  2. Axial depressions present
  3. Axial depressions contain small costae

Symmetrical biraphid - Frustules of Microcostatus are small in size. The axial area includes lyre-shaped depressions on both sides of the prominent sternum. The depressions contain small costae (microcostae) in a depression near the axial area. Striae not visible with the light microscope. SEM reveals striae are present and comprised of single rows of areolae. In living cells two plastids are present, pressed to the cingulum. The genus differs...


  1. Striae composed of microfissures
  2. Frustules small
  3. Intermissio present

Symmetrical biraphid - SPECIES OF MICROFISSURATA ARE NOT KNOWN TO OCCUR IN NORTH AMERICA Species are comparatively small and usually live as solitary cells. Valves are lanceolate or linear elliptical, with protracted ends. The axial area is wide or very wide, especially in the central area. The central area is an expanded fascia. Externally, the striae are open slits, termed microfissures. Internally, the microfissures are closed and covered...

Muelleria 4

  1. External proximal raphe ends deflected to one side
  2. Longitudial canals two, one on each side of the raphe

Symmetrical biraphid - The outline of valves of Muelleria is linear, linear-elliptical or panduriform. The external proximal raphe ends are distinctive for their unilateral deflection. Distal raphe ends are branched. A longitudinal canal is present on each side of the raphe. Areolae are loculate. Living cells contain four plastids. Muelleria gibbula and M. terrestris appear to be widespread in aerophilic habitats, in association with soils,...