The Ravener is a creature with scythes and a slimy tail with hooks; it is the Lictor's "cousin". They tend to crawl or "slither" forward in secret and attack enemy units, catching them off-guard.
Some time ago there was a great Ravener who was greatly feared among the Tyranid race. It had a large mouth to eat, and was very large. It had six scythes on its body along with large hooks on its tail. It was killed in the last great war of the Tyranids while battling against other races.