com·men·sal 
(kə-mĕnsəl)
(kə-mĕnsəl)adj.
Of, relating to, or characterized by a symbiotic relationship in which one species is benefited while the other is unaffected.
n.
An organism participating in a symbiotic relationship in which one species derives some benefit while the other is unaffected.
[Middle English, sharing a meal, from Medieval Latin commēnsālis : Latin com-, com- + Latin mēnsa, table.]
com·mensal·ly adv.