Ravener
A Ravener is an assault-specialized Tyranid creature, much like the Space Marines' Assault Squads. They both focus on being in close quarters, they both can ignore difficult terrain (though Raveners do so by running through it rather than jumping over it), and they are both ill-suited for dealing with lots of dakka. Being Beasts and having Fleet also helps them to harass some unsuspecting targets, but not for any long fights with MEQs. Being fitted with Deathspitters allows them to threaten AV10, but given their limited BS and that they need 5+ to damage AV10 this is a last-ditch effort at best.
While primarily melee units Raveners can still be armed with ranged weapons, albeit at a higher than average cost. Notable is that their weapons are not fused to their limbs: instead they are located in their chests to not reduce any of their melee capabilities. The cheapest weapon Raveners can be armed with is a pair of Spinefists, which is a decent weapon when dealing with large numbers of light infantry like Guardsmen. They can also be fitted with Devourers, which are slightly more expensive and hit harder and at a longer range, but are not twin-linked and lack the AP of the Spinefists. Finally they can be armed with Deathspitters that take the best of both worlds: long range, armor penetration and a threatening Strength 5 at the cost of being twice as expensive as the Devourers. Raveners can also replace one pairof Scything Talons with Rending Claws to give them AP5 on their attacks and become capable of dealing with tougher enemies.
In Dawn of War II one of the heroes for the Tyranids is the Ravener Alpha, which is essentially just a bigger Ravener. It takes a page from the Trygon's book and and can build large tunnels for allied units to crawl through.