1) Yellow-green algae 
green algae that floats on surface of stagnant water
• (n.) Any unbranched, slender, green plant of the fresh-water algae. The word is frequently used in a wider sense.
Con·fer'va noun ; plural Confervæ . [ Latin , a kind of water plant. See Comfrey .] (Botany) Any unbranched, slender, green plant of the fresh-water algae. The word is frequently used in a wider sense. 
[n] - any of various algae of the genus Tribonema
noun any of various algae of the genus Tribonema; algae with branching filaments that form scum in still or stagnant fresh water
any simple filamentous green algae, many of which were formerly classified in the genus Conferva.