Dudes, these monsters are the same damn thing. Just because highly creative artists have attempted to illustrate them differently doesn't mean they're not.
Gygax's Kuo-Toa are basically nothing more than a re-worked Sahuagin (the latter NOT a creation of Dave Arneson per Gary, though their first appearance in D&D IS in the Blackmoore supplement). The wikipedia states Gygax claimed them as a creation of Steve Marsh, but I can't help but this, like EGG's own fish-men, may have been an attempt (in part) to help bury or sublimate another o Dave's creations.
[nah, I'm not a conspiracy theorist, and I generally give Gary the benefit o the doubt, but business is business, right?]
Let's compare, shall we?
Armor class 5 or AC 4. Hit dice 2+2 (or more), HD 2 (or more)...both continue to grow in size with age. Sahuagin "wear a harness to carry their personal gear and weapons;" Kuo-Toa wear "only leather harnesses for their weapons and a small amount of personal gear." Spears, daggers, nets, crossbows and tridents for one group...spears, daggers, nets, short bows and harpoons for the other; PLUS gluey shields and pincer staffs for the Kuo-Toa. Both have aversions to sunlight, both are amphibious, both capture humans for slaves, sport, and sacrifice. Both have cleric-priests, culture, extensive histories of bad blood with creatures of the surface world. Both have sharp teeth for when they get in close and personal.
Of course, Gygax's Kuo-Toa are over complicated (IMO) by the addition of character classes to the monster. Oh...and they can join hands and shoot lightning.
Now the reason I'm looking at these critters at all is because I want something like the Sahuagin or the Kuo-Toa in my game. I LIKE both of these monsters (well, except maybe the whole lightning thing...I forgot all about that!), and a semi-barbaric/semi-civilized race of evil aquatic beings bent on world domination (or at least bent towards making the surface dwellers miserable) is immensely pulpy and fantastic. In other words, it's imperative (again, my opinion) to include some sort of amphibious, diabolically organized humanoid.
Lovecraft's Deep Ones are barbaric and organized and they, too, have their own weird religion and priest caste (if you can call their particular form of ancestor worship the same as a clerical religion). The Call of Cthulhu RPG gives them a spear attack or claw. I also dig the whole human/Deep One-hybrid thing. In addition to being exceedingly creepy, it's a twisted version of the classic halfling- (i.e. half-human/fae, not hobbit) or changeling-type of folk tale.
Now, it's been written that the Kuo-Toans are Gary's homage to HPL's Deep Ones, and that the Sahuagin are based on the Maori folklore of the under-sea goblin the Ponaturi. Whether or not Lovecraft's Deep Ones are modeled after the Ponaturi is a whole different subject...um, as is the story that Sahuagin are based on an episode of the Super Friends cartoon (I watched the Super Friends as a kid and I don't remember cannibalistic underwater dwellers...maybe I've suppressed the memory?).
Anyway, for my B/X Companion I'm doing a combo-pastiche of all these critters. For the sake of Hasbro and Chaosium's intellectual property, I'm naming 'em after the historic legend...oh, and I'm leaving out the lightning bolts.
From Part 6: Monsters (B/X Companion):
Armor Class: 4.............No. Appearing: 1-6 (6-36)
Hit Dice: 2+2.............Save As: Fighter 3
Move: 150' (50').............Morale: 11
Attack: 2 or 1 Weapon.............Treasure Type: M
Damage: 3-6/3-6 or 1D8+2.............Alignment: Chaotic
Ponaturi are an ancient race of evil, amphibious humanoids that live in the deepest depths of the ocean or undersea caverns. They can breathe both air and water, but generally only venture to the surface world to collect humans for food, sport, slaves, and sacrifice. On land, their movement is only 90' (30').
The ponaturi live for hundreds of years and grow larger and stronger with age. An average adult ponaturi is over 6' tall; the oldest are more than 21' tall and have 17+17 hit dice and do 12-24 points of damage with each claw attack (each extra foot of height adding an extra 1+1 to hit dice; each extra 5' of height multiplies damage by one additional factor). They save as fighters of the same HD plus one (except clerics, see below).
Ponaturi live in large cities far from the eyes of the surface world. They have clerics (spell level equal to hit dice, add one * to hit dice for every 2 or fraction of 2 spell levels), and war parties of 20+ individuals will generally have a cleric of level 3-8, plus a leader of HD 5-9. Ponaturi have webbed claws, scaly hides, and dead black, shark-like eyes that allow them to see well in the dark but make them vulnerable to light (-1 to hit and saves in even torch light, -2 in full daylight). When armed, they generally wield harpoon-like spears, barbed nets, and large serrated daggers.