34 ALGAE IN PHYTOPLANKTON OF THE UNITED STATES 



Division Chlorophyta 

 Class Chlorophyceae 

 Order Chlorococcales 

 Family Micractiniaceae 

 GENUS MICRACTINIUM Fresenius, 1858 (fig. 11) 



MORPHOLOGY 



Cells are spherical to broadly ellipsoidal and 4-8 ^m in diameter. The 

 single, cup-shaped chromatophore is parietal. Each cell bears 1 to 7 

 long uniform setae. Cells generally are quadrately united in a 4-celled 

 coenobium. Several coenobia are generally united. 



REPRODUCTION 



The cell divides asexually into 4 autospores, which are released when 

 the parent-cell wall ruptures into 4 symmetrical parts. Oogamous sex- 

 ual reproduction is by the union of a biflagellate antherozoid and an 

 egg. The egg protrudes through an opening in the cell wall at the time 

 of fertilization. Following fertilization, the zygote moves through the 

 opening and becomes attached to the parent-cell wall. 



OCCURRENCE 



Free-floating colonies are common in the euplankton. It is generally 

 indicative of soft- water conditions. 



ENVIRONMENTAL CONDITIONS 



Standard 

 Range Mean deviation 



Temperature degrees Celsius 0.0 - 



pH 5.9 - 



Dissolved oxygen milligrams per liter .1 - 



Specific conductance micromho 11 



Total alkalinity milligrams per liter 



Total hardness do 6 



Total nitrogen do .03- 



Total phosphorus do .0 - 



SPECIES INFORMATION 



Refer to Tiffany (1934), Smith (1920), and Prescott (1962). 



