• Category
  • Diameter
    5.6–10.0 µm
  • Striae in 10 µm
    48-51 at valve margin



Live cells are organized in chain-like colonies, linked by a single chitin thread between each center valve. In girdle view, cells are rectangular, with a rounded valve/mantle interface. Multiple plastids are present in each cell. The pervalvar axis is about one half of the valve diameter. Cells in the chain are spaced at approximately 2x the pervalvar distance.

Acid-cleaned valves are relatively non-descript in LM. The pattern of areola is rarely visible. Critical focus reveals a ring of marginal fultoportulae regularly spaced at 30°- 45° intervals, and a single, wide, radially-oriented rimoportula positioned between two of the marginal fultoportulae. Two characteristic, closely-spaced, fultoportulae are present at the center of the valve.

SEM observation reveals nearly flat valves. The valve mantle is shallow and indistinct. Areolae are radially-arranged, irregular, and hexagonal in shape. The areolae are loculate, with circular external foramina and cribrate internal occlusions. Externally, the outermost siliceous layer is often more developed toward the valve margin with the less developed areas around the center of the valve face. The outermost siliceous layer on more heavily silicified valves exhibit rings of siliceous granules surrounding small circular apertures. The external tubes of the marginal fultoportulae are short and located at the valve-face and mantle junction. A short occluded process is located on the valve face, near each marginal fultoportula.

Internally, the velum is well-developed and perforated by discrete cribra with multiple small pores. The number of pores in the cribrum of each areola increases from the valve center toward the valve margin. The marginal fultoportulae are surrounded by four satellite pores. Two central fultoportulae are surrounded by three satellite pores.

Hasle (1980) examined the type material and provided detailed description of valve and cingulum ultrastructure.

Cells are often obscured by attached detritus (Kraberg et al. 2010).

Coscinosira floridana Cooper 1958 is a latter heterotypic synonym.


This taxon is planktonic and form in short colonies of 2-20 cells. The cells are connected by central chitin threads. Colonies often accumulate detritus (Kraberg et al. 2010).

Thalassiosira minima AE1
Credit: Tom Frankovich
Colony of four cells joined by chitin fibrils. Scale bar = 10 µm.
Thalassiosira minima AE2
Credit: Tom Frankovich
Colony of four cells, detritus attached. Scale bar = 10 µm.
Thalassiosira minima AE3
Credit: Tom Frankovich
Colony of four cells, scale bar = 10 µm.
Thalassiosira minima AE4
Credit: Tom Frankovich
Two cells, chloroplasts visible, scale bar = 10 µm.

Original Description

Thalassiosira minima n. sp.

Fig. 18.

In samples from two stations in the region between Ireland and Spain a few chains of a very small Thalassiosira occurred, which it has been impossible to identify as one of the species described in the literature at hand. It is, therefore, like T. coronata, preliminarily treated as a separate species.

It has only been studied in water. The chains consist of up to 8 short cells combined by a thin flaccid central thread. The distance between the cells varies from 6 to 9 µ in the same chain. The longest distance measured is 18 µ (in cells with a diameter of 7 µ and a height of 3.5 µ). The diameter of the cells measured 7-14 µ and the height 3.5-6 µ. The proportion height/diameter (h/d) is mostly 1/2, min. 3/7, max. 3/4.

The valve face is flat, rounded at the margin and with a slight depression around the slime pore. The girdle zone is low. In water neither copulae nor spines or valve structure could be distinguished. The chromatophores are relatively large irregular discs (fig. 18b).

  • Author
    Gaarder 1951
  • Length Range
    7-14 µm
  • Width
    3.5-6 µm

Original Images

Thalassiosira minima orig illus
Thalassiosira minima orig desc

Citations & Links



Cite This Page

Frankovich, T. (2021). Thalassiosira minima. In Diatoms of North America. Retrieved December 01, 2023, from https://diatoms.org/species/thalassiosira-minima


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