Final answer:
The anticoagulant secreted by leech salivary glands is Hirudin. It acts as an anticoagulant by inhibiting the enzyme thrombin, preventing blood clot formation.
Step-by-step explanation:
The anticoagulant secreted by leech salivary glands is Hirudin. The leeches secrete this substance into their saliva when they bite a host. Hirudin acts as an anticoagulant by inhibiting the enzyme thrombin, which is responsible for the formation of blood clots. This allows the leech to feed on the host's blood without the blood clotting.