Figure 7From: External and internal shell formation in the ramshorn snail Marisa cornuarietisare extremes in a continuum of gradual variation in developmentSketches of three different developmental stages (aged 3 (frontal view) and 7 days (left lateral view) and after completion of embryonic development (left lateral view)) of normal (top row), “partly-shelled” (middle row) and “sluggish” individuals (bottom row). Black: mantle tissue; red: shell gland; yellow: shell, direction of growth is indicated by an arrow, arrest of growth is indicated by X; F: foot; VS: visceral sac.Back to article page