Thought I knew this but just want to double check. A Troll has the following attacks listed:

Melee bite +8 (1d8+5), 2 claws +8 (1d6+5)
Space 10 ft.; Reach 10 ft.
Special Attacks rend (2 claws, 1d6+7)

Do the claws count as one attack or two? Same for rend.

Assuming a troll starts in melee combat with an opponent, does he get 3 attacks all together and an additional 2 if claws hit? Bite hits? One claw hits?

I believe that that indicates that the Bite is the primary attack.  At first I thought, Claws would be a secondary attacks.  Secondary attacks take a -5 to hit, unless the monster has the Multi-attack feat.  The rend attack, is a special attack, and part of its definition requires you succeed in both your claw attacks, allowing you an additional rend attack that round.  If you look at it however, you note... the bonus to hit was not reduced by 5, so that is a clue that claws are also considered primary.

Note:  A monster has several attacks, but to take more than one attack in a round, it has to take a full attack action.  [assuming no extraordinary feats such as pounce involved] So normally when a monster moves in to attack, it will only have a standard action (or they are doing a charge action which allows a single attack) and thus will only get to utilize one of their attacks that round.

If they can continue to attack, only using at most a 5' steps for movement, they can start using full attacks and use all their attacks.

http://www.d20pfsrd.com/bestia...#TOC-Natural-Attacks

Above is a table to reference.

Hope it helps.

The math has been done regarding primary and secondary attacks, so you don't have to adjust the numbers any. The creature isn't limited to only using the first attack if it only gets one, it can choose to claw instead of bite if it wants.

The rend ability kicks in whenever the specified attacks all hit (in this case, both claws), and automatically inflicts the listed damage with no additional attack roll. Note that a rend attack cannot score a critical hit, because it doesn't get an attack roll.

To answer the original question, yes it has two claws. A full attack is one bite plus two claws, with an additional rend if both hit.

In reply to Flint_A (msg # 4):

Why do its claw attacks have the same attack + as the bite? Shouldn't they be secondary and at -5?

Why rend only if both claws hit? Under Universal rules it says rend happens if any natural attack hits?