All close combat symbiotes count as special close combat attacks and are therefore only effective if the Tyranid model is in base-to-base combat, or within 2" and has the Leaping special rule (lash whips are an exception to this, see opposite for details). However, a Tyranid creature can use all of its close combat symbiotes in an assault and is not only limited to using one at a time like most models.
Many Tyranid creatures have long stabbing and slashing claws of razor-edged bone or chitin. The reach and sweep of such talons enables them to attack murderously at close quarters, eviscerating their victims with a flurry of blows.
Tyranid creatures with scything talons count as having two close combat weapons in an assault and so gain +1 Attack. Creatures with two sets of scything talons gain +2 Attacks in close combat instead of +1. No more than +2 Attacks can be gained and the number of shots with Assault X weapons is not increased by scything talons. Note that this is the only way that Tyranids gain extra Attacks in close combat for multiple weapons, their number of limbs is accounted for in their basic profiles.