Ok, here's an all encompassing post with everything you need to know to complete the Mudrock Soup and Bugs (Forked Mudrock Tongue) quest.

I solo'ed this quest as a full fire spec level 37 human mage. The tongues drop rate is not very high, but the quest is not hard at all, and the level 35-40 Mudrock Tortoises/Burrowers/Spikeshells are quite easy to kill.

Receiving the quest:

Go to the Mage's Quarter in Stormwind, and enter the Blue Recluse pub. You will get a quest called 'Morgan Stern' from a barman.

Travel to the Wetlands, then take the boat on your left side as you face the ocean to Theramore.

Once in Theramore, find the inn at 66, 45 (Northmost point of Theramore) and speak with Morgan. He will complete the quest, and you will begin the Mudrock Soup and Bugs quest. You will get 700 experience for completing this part of the quest, and 28 Stormwind experience.

Directions:

To get to the Dreadmurk Shore (where the tortoise are) go to co-ordinates 64, 41.

If you do not have co-ordinates, as soon as you leave Theramore and cross the bridge, take a sharp right until you hit the beach. North, up the beach, you will find the Mudrocks.

Drop rate:

I killed 19 Mudrocks to get the 8 tongues needed. Each Mudrock gave an average of 230 experience (I am level 37). This experience adds up to: 4370 experience.

Bonus:

If you go about 61, 27 (halfway up the shore), and look across the sea, there is a little Mirefin hut surrounded by about 5 Mirefins. At my time there, there was a chest. The hut is a chest spawn point, so check if there is one. If there is, you will have to kill 1 Mirefin on his own infront of the hut, and 2 at once who defend the chest. Then, reap the rewards. I received (among some foods) 'Formula: Enchant Shield - Stamina'.

Alternative directions:

You do not have to go to the beach to get the Mudrocks. Instead of taking a sharp right out of Theramore, take a sharp left and you get to a bay with alot of tiny islands. There are Mudrock Burrowers around there, but I don't advise doing the quest here, as there are also some level 40 beasts which cause some annoyance. Co-ords for this are 62, 47.

Experience total:

Stormwind -> Theramore (Speak with Morgan): 700exp
Killing Mudrocks: 4370
Quest completion: 2850

Total experience: 7920

Reputation total:

Stormwind -> Theramore (Speak with Morgan): 28 rep
Quest completion: 275 rep

Total reputation: 303

(Please remember all this is based on me being level 37. If you are less than 37, you will probably get more, and if you are higher you will probably get less).

Have fun.

I was out here last night doing some grinding and spotting for a 33 Druid just in case they got into trouble when 46Elite Coral Shark came out of the water and aggro'd the Druid. We ran up onto a hill over the beach, and sure enough the thing was fully out of the water and on the beach as we watched it search around for us. I didn't think they'd actually leave the water, but they do and I wished that I'd gotten a screenshot of it. A rare occurance I would guess, but keep your eyes open and don't afk near the edge of the water in this area.

Erm, I remember when I did this quest that I got a crappy drop rate too, around 50 kills to get the 8 tongues. Maybe some servers give better drop rates than others on these mobs?

Head up and down the coast North of Theramore. The turtles are level 36-37, and the droprate is fairly low, so you'll be killing a lot of them.

They do drop the Thick Scaly Tails and Speckled Shell Fragments, though, so it's not all that bad of a grind. They're gray, but they sell for a decent amount to vendors.