Reefclaws have 2 Claws +2 (1d4 + Grab + Poison) as their melee attack. They also have Constrict (1d4) as a Special Attack
If a Reefclaw succesfully grapples an opponent, decides to maintain the grapple in its next round and takes the "inflict damage" option following the succesful maintain, damage should go like this:
Successful Grapple: 1d4 Constrict Damage
Inflict Damage: 1d4 (because thats the damage of its natural attack)
Will the poison effect be applied?