Tubifex worms (Tubifex tubifex) are indicator species that thrive in heavily polluted, stagnant river beds where dissolved oxygen concentrations are near zero. They live buried head-first in the sediment, waving their tails—which contain high concentrations of the respiratory pigment hemoglobin—directly in the water column.
Give one reason why waving these hemoglobin-rich tails helps them survive in these oxygen-depleted environments.
