Exocrine
The Tyranid Exocrine is a huge living weapon with a carrier beast. This creature is actually two Tyranids in one: The huge gun on its back which can fire a huge ball of plasma or several small streams, and the Exocrine itself, which is just a mule to carry the gun and protect it.
The gun itself controls the Exocrine and can only fully concentrate on targeting and firing when it mentally smacks the dull creature to stop moving about. This has led many Imperial observers to believe the gun is actually more intelligent than its carrier and endless lolz in the fanbase as the completely sensible question of why an intelligent, evil overmind like the Hive Mind would create such a weapon with the drawback of being unable to fire if the carrier even twitches a little (this sounds familiar...) Other lesser bio-morph weapons seem to not have the trouble of a mindless oaf to worry about after all. This in turn remind all of us on why the Nids are even considered the "Master of Evolution" if they can't even get their own Artillery Units right, let alone Apocalypse units such as the Harridan which dies the moment it lands, since for some fucktarded reason, having EXBOXHUGE wings is apparently a one-use card now. One must wonder what the flying fuck the Hivemind was smoking when it decided that these "Units" was considered as "A-OK!".
Regardless, the Exocrine is the most feared of the ranged firepower creatures in the Tyranid army. This is not much of a compliment for a race renowned for poor firepower, on par with the Orks and their wild chaotic shooting sprees. Although to be fair, the Exocrine is at least a more badass and cooler version of the Pyrovore,and at least it is MUCH more useful than that fiery fuck of fail.
The Exocrine's problem on the tabletop can be summed up simply; 24 inch range. Its ability to spam TEQ-fucking shots in an army with such little MEQ or better busting shooting would be invaluable but despite being a living artillery weapon it has to get within twenty four inches, and thus in the range of other people's plasma shots and most of the weapons TEQs use. Secondly, cover is fucking everywhere and the Tyranids don't have all the "lol cover saves" options that diviniation spammers, template lovers, and tau players get. And finally, despite it being an organism evolved solely for ranged combat, its BS is still kind of sucky.
All of this has added up to a good unit with a unique role in the Tyranid army, but not one that can hold a candle to the sheer frustration the likes of Iontides or Heldrakes unleashed and exemplifies GW's bad and inconsistent game design.
36" range in 8th WOOP WOOP!
The creature is named after exocrine glands, glands that produce a substance and move it to somewhere outside of the body by ways of a duct. Think things like sweat, tears, gall, and milk. Given how the creature works, it's presumably a rather destructive version of such a gland.