Only 1 Hivemind

8th Ed Codex [Tyranids]:

"The Magos Biologis of the Imperium categorizes each Tyranid hivefleet as a separate force, an individual entity that competes with other hive fleets for resources. Indeed, each is self-sufficient, appearing to exhibit different strategies and developing unique creatures to overcome its prey. However, the truth is more complex, for each hive fleet is but a splinter of one greater assemblage. The Tyranids’ numbers are vast beyond counting, swarms so large that they block out the very stars, yet each and every creature is but a single cell in the living body of a single super-organism.

Every thought and action, every spark of life in the Tyranid race, is bound and interlinked into a single unfathomable consciousness, a great entity that stretches across hundreds of light years of space. This gestalt sentience is known as the Hive Mind. It holds all Tyranids in a psychic bond that enables them to act in perfect synchronicity..."

• 9th Ed Codex [Tyranids]:

"This monstruous entity, is known as the tyranid race even by naming the "GREAT DEVOURER" civilizations betray their ignorance, every thought and action, every spark of life in the tyranid race is bound and interlink into a single mind, a single great entity that stretches over light years of space and is controlled by the immortal Hivemind."

• White Dwarf #145:

"Beyond the human galaxy lie the vast uncharted regions of intergalactic space. Empty distances too vast to comprehend thwart all of mankind's attempts to navigate them. These are the great barriers which separate galaxy from galaxy and keep the farthest stars the subject of conjecture and mystery. Now something stirs in the frozen emptiness. An intelligence moves through it, a mind that is many inter-linked minds, immeasurably old and alien. This is the Tyranid hive mind, and it has crossed the great, dark void in search of new planets to despoil. Now its advance forces have reached the Imperium, and the fate of mankind and every living thing in the galaxy hang in the balance."