A while ago there was a thread about beast arenas. It brought up the fact that 2/3 of the monsters in there weren't even beasts, and like half of them actually resisted piercing. Indeed, in addition to the throngs of gremlins that spawn there are numerous lumbers, mecha-knights, jelly cubes and polyp turrets. The turrets are always a special pain because of how much area their bullet walls deny within arenas' small floor plans, making the best strategy be to take them down as quickly as possible, but polyp spawns are particularly difficult in beast arenas because they resist the type of damage that's supposed to be good for that floor (in fact they are very resistant to it since most pierce weapons do pure piercing damage). Arguments that arenas are supposed to be challenging and that people should be prepared with multiple damage types are fair, but the fact is that you'll never see a howlitzer in a jelly arena or a polyp in a fiend arena.
The problem with polyps extends beyond arenas. Though turrets in general aren't nearly as threatening in areas that provide cover and room to run, they still suffer from a noticeable imbalance in resistances. Of the three turret monsters, two are weak to elemental and none resist it, while none are weak to piercing and two resist it.
Even putting balance aside, the beast family is still the least diverse family, having only three different species (three and a half including alphas, to be fair), no "special" units like turrets or healers, and no rare spawns. For all the fans they have, they're actually one of the least interesting families.
And so I'd like to propose the addition of beast-family turrets. Below are two concepts of burrowing beasts (each with three tiers) I drew up in hopes they could at least provide some inspiration as to what kinds of things might work. I give you...
http://imageshack.us/a/img28/931/f274.png
The spit viper, a snake-based turret that spits fang-like projectiles. As a special quirk, perhaps all spit vipers could do poison in addition to their stage-appropriate statuses, with poison-themed vipers doing stun or extra strong poison or something. Maybe not.
http://imageshack.us/a/img13/6518/wr1j.png
The porcuspine, a reclusive rodent that digs burrows with its powerful claws and responds to threats by curling into a ball and launching sharp quills at aggressors. I wanted to give the T3 version white stripes on the quills, similar to what real porcupines have, but the brush strokes just made it look awful. An actual artist might have better luck.
Just for fun, I also made a quick concept for a fiendish turret. Maybe it could be called a "morning star" or something. Would hardly be necessary since howlitzers don't resist piercing and are suitable for fiend levels, but eh.
http://imageshack.us/a/img845/1816/4aia.png
There's a reason there's no beast turrets ingame ;)