Huntail

Huntail lives close to the bottom of the sea.  To withstand all the crushing underwater pressure deep in the sea, this Pokemon has a thick and sturdy spine.  It uses its fish-like tail to lure prey towards it.
Huntail looks awesome.  It has a great design and high Attack and Defense stats.  It's good to have high Attack Defense stats.  He also has acceptable Sp. Attack and Sp. Defense stats.  The only flaw is that Huntail has low HP and Speed stats, but at least you have high Attack and Defense stats to make up for those.
It's okay to give Huntail some Special moves if you want, but Huntail is obviously more useful when it's Physically based.  You could use moves like Crunch, Aqua Tail, or Dive.  You also have Baton Pass, which is useful if you use moves like Clamp, Iron Defense, or Shell Smash.  You have a decent Sp. Attack stat, so you could give it some Special moves if you'd like.  Huntail is just more useful with Physical moves, though.
Your ability is Swift Swim.  In Rainy weather conditions, Huntail has its Speed boosted.  Seeing as how Huntail is slow, this ability is great.  Use something like Rain Dance to automatically make it  rainy in battle.  This ability will almost certainly turn the battle around when you're using Huntail.
Huntail is an awesome Pokemon with a great design and great stats, as well as an acceptable movepool.  This isn't the Deep Sea Pokemon- it's the beast Pokemon.