Yeah, it's a shame the underwater monsters are so weak, I'd much rather grind with them than the generic human enemies in the Crystal Tower.
EDIT: MacGuyver, how much would it cost to buy a Hermit or Mandrake from you?
Here's some Amano art to sweeten the deal. Also, some more analysiseses:
Slime/Red Marshmallow/Black Flan



I like the disgruntled expression, and the way he sort of looks like a living blanket.
Tarantula/Darklegs


Love those spindly legs! I also like the distressingly human teeth. Unfortunately, this design was completely butchered in the DS version:
Why, Squeenix?! Why?!Harpy/Dira


I was originally going to write this off as a generic sexy monster chick, but there's actually some pretty cool details, like the tentacle-like hair and the wings instead of arms. It really looks like a bird that just sort of evolved humanoid features.
Gargoyle/Rock Gargoyle


Nothing much to say.
Chimera/Chimera Mage


It's a... chimera. Nothing to separate it from other chimeras. The Mage's palette is pretty cool.
Demon Horse/Nightmare


It's a fairly standard horse enemy, but the Nightmare does have that awesome golden palette.
Bovian/Minotaur


Nothing much of note, but I do like the expression.
Dread Knight/Gold Knight


I like to think he's sort of flying around using his feet as boosters. FWWWWWWWWWWSH
And of course, more gold.
Abtu/Anet


I love the horn, it makes it look like some sort of demonic narwhal. Its mindless eyes are also cool.
Kagura/Seahorse/King Seahorse



I like the horn on this one, too. I also love the similarities between the Kagura and Seahorse palette, and of course there's that amazing gold palette. I have no idea why I like that one so much.
Charybdis/Remora


I love the camouflaged look, this guy kind of looks like it could fit into real-world ecology. I also love Remora's palette.
Sea Witch/Mermaid


Though the sprites are fairly uninspired, Amano's original art does have an excellent cybernetic bent, and I don't know why they decided to drop it:

Ologhai/Plancti


I love the monstrous face, tentacles instead of legs, and odd square build. Takes "crab monster" in the best possible direction.
Kelpie/Sea Lion


Based on a dumb pun, but I like the jewelery. Lends them an air of civility.
Aegir/Agaliarept


Mostly speaks for itself, but I like the asymmetrical eyes. Almost seems like a more powerful Carbuncle.