Video B. Inner demibranch of Dreissena polymorpha as observed through the endoscope (looking medially). Side view of the ventral margin of the inner demibranch (center of frame) and the visceral mass (background). Particles (green alga, Scenedesmus quadricauda) are moving anteriorly in the superficial groove of the ventral margin. The presence of a superficial mucous string, as opposed to particle slurry, is confirmed in this sequence in which the string is dislodged from the ventral margin by a contraction of the gill. The superficial mucous string remains unbroken and returns to the ventral margin of the demibranch.