Related Clues:

• One-celled critter
• Sea lettuce, e.g.
• One-celled organism
• Plankton component
• Marine biology subject
• One-celled creature
• Primitive creature
• Creature with pseudopods
• Chlorophyllous plant
• Unit
• Aquatic plant
• Microscope sight
• Pond floater
• Pond scum component
• It lacks roots