TAXONOMIC KEY 9 



TAXONOMIC KEY TO THE IDENTIFICATION OF COMMONLY 



OCCURRING AND DOMINANT GENERA OF ALGAE 



OBSERVED IN THE PHYTOPLANKTON OF THE 



UNITED STATES 



[The following key consists of couplets of characteristics. One must decide which state- 

 ment of the couplet most accurately describes the specimen. Having made a selection, 

 proceed to the couplet indicated by the number to the right. Continue through the key un- 

 til a genus is indicated. The key is constructed for the 58 genera described in this report. 

 The identification of other genera requires the use of a more comprehensive key.] 



1A Plant pigments contained in chromatophores 



or chloroplasts ^q 



IB Plant pigments not contained in chromato- 

 phores or chloroplasts, but diffused 



through protoplast 2 



2 A Plants filamentous; cells arranged 



in trichomes 4 



2B Plants colonial, not filamentous 3 



3A Cells in regular rows, generally in multiples 



of four; colony one cell in thickness Agmenellum 



3B Cells somewhat evenly arranged toward 

 periphery of spherical colony; barely 

 visible gelatinous strands radiate from 



center of colony to cells Gomphosphaeria 



3C Colony asymmetrical; cells very dense and 



unevenly distributed Anacystis 



4A Filaments straight or slightly 



flexed 6 



4B Filaments curved, twisted, or 



spiraled 5 



5A Heterocysts and akinetes present Anabaena 



5B Heterocysts absent Raphidiopsis 



6A Heterocysts present 9 



6B Heterocysts absent 7 



7A Filaments without a sheath; cells discoid Oscillatoria 



7B Filaments with distinct sheath 8 



8A Trichomes tangled; sheaths con- 

 fluent Phormidium 



8B Trichomes separate; sheaths not 



confluent Lyngbya 



