Nautiloid
The Nautiloid is a massive species of Tyranid that...welll....looks like an overgrown nautiloid on land. Carrying a massive shell that looks like it can tank a number of its, its mid- and rear-limbs are fused into a pseudopod and Lash Whip combination.
Not much is known about this critter other than appearing in a rather illusive and unknown Warhammer 40,000 Collectible Card Game (Yes as hard it is to believe, WH40K had a card game). It is unknown what its main purpose was as its assumed slow speed and lack of range weapons makes the Nautiloid...mysterious. It could be assumed that it is only dropped when the Hive Mind knows there is very little defense on a planet and drops these suckers in to help gobble up any microbial or hard suck out organisms. Heck they might be the ones responsible of sucking out the planets micro-organisms in the first place.