Rhizoclonium rivulare

from The Collaborative International Dictionary of English v.0.48

Crow-silk \Crow"-silk`\ (kr?"s?lk`), n. (Bot.)
   A filamentous fresh-water alga ({Conferva rivularis} of
   Linnaeus, {Rhizoclonium rivulare} of Kutzing).
   [1913 Webster] crow's-nest