التعريف: microscopic algae, typically found in freshwater and marine systems, living in both the water column and sediment. They are unicellular species which exist individually, or in chains or groups.
التعريف: aquatic organisms that construct and inhabit simple unbranched vertical shafts with only one opening to the surface. These are primarily above-sediment filter-feeders, surface deposit-feeders, and subsurface deposit-feeders (head-down, conveyor-belt feeders)
