A drawing of an alien with tentacles
A tentacle or tendril was a flexible, elongated organ present in some species of animals or alien lifeforms.
The space vessel lifeform had matter/energy tendrils, which they used for touching the tendrils of other members of their species. (TNG: "Encounter at Farpoint")
An alien in Haley's 2151 drawing "First Contact" had tentacles. (ENT: "Breaking the Ice")
The Vendorians were known to have tentacles, as were the Ba'Neth. Kelvans in their natural form were immense beings that had a hundred tentacle-like limbs. (TOS: "By Any Other Name"; TAS: "The Survivor"; VOY: "Riddles")
A symbiotic lifeform which managed to gain access to the NX-class starship Enterprise NX-01 in 2152 snared several crewmembers with tendrils. (ENT: "Vox Sola")
In 2370, Julian Bashir was almost strangled by the tentacle of a metamorphic lifeform, actually a mutated Odo. Bashir injured the creature by cutting its tentacle with a laser scalpel. (DS9: "The Alternate")
In 2373, the tentacle of a creature grabbed Kira Nerys' hand when a serpent worm was delivered to Deep Space 9. (DS9: "A Simple Investigation")