Slothunog

[Leatho Shellhound]

But fishing, swimming and row boating could be done on it.

[321tumbler]

In High Rhulain it says(talking about Cuthbert), "in the last of his many roles, a dragonslayer."

[AxeHound]

Looks like a dragon in the picture on page 2.

[Kitsune]

No clue.

[Russa Nodrey]

I have this incredibly weird, totally indescribable image in my mind, when ever it mentions him.

[JangoCoolguy]

A completely random sea monster

[The Skarzs]

I've said it before on another topic: possibly based on the Loch Ness monster.

[Gonff the Mousethief]

Well, this whole thing would have been a LOT cooler if it was in the highland, NOT on an island. Then I could call it Nessie! Anyway, I agree with Skarzs on this one. Probably based on Nessie.

[Cornflower MM]

I don't know...I always thought he/she/it was just a really frickin' huge eel.

[Hickory]

*revive*

Not an eel, it is too... big. An ancient monster, and leave it at that.

[Feles]

Youre comment, plus your profile pic
reminded me of another ancient monster

off topic, im sorry

It could quite well be an eel, considering how big adders are

[Rivertheotter]

Well, Whatever it is, it must have been really old. my theory is that it is some mutant creature, or a plesiosaur, or some loch-ness-monster-type creature.

[Hickory]

*revive*

Not an eel, it is too... big. An ancient monster, and leave it at that.

IKR 

[Feles]

actually, now that a think about it, there is only one eel in the Redwall series, cant remember the book, but it was during Abbess Tansy's time
i still stand firm on the it being an eel, they are adder sized, or close to it and that creature was definitely the right size for and Adder

This actually makes me think it could be a water snake

[The Skarzs]

In the Long Patrol, Skipper fought an eel in the subterranean waters flowing through and under the sunken parapet that had once belonged to Kotir.