Sleri

The Sleri were a species of tentacle-like aliens, created by the Undine, who were self aware. 

They could communicate in space to starships by emitting high frequency bio-electric waves, and also had the ability to shock anything they came in contact with by generating massive amounts of bio-energy. ("The Nega'Jem, Part II")

History
In 2410, in fluidic space, the Undine scientist Kohogeth admitted to "having (Sleri) from the very beginning" and had reached the point where he had thousands of them. He used them to attack and control Winry when he was attempting to convince Aeris to stay with him, but Winry convinced the Sleri to help her take back the biobase they were in and help the two women return to the prime universe. (: Pages 23-24)

Sleri (mirror)
In 2377, a colony of mirror universe, giant Sleri tentacles, created by and brought from the Jem'Hadar of the mirror universe, lived in an asteroid belt in the prime universe. When the separated sections of the USS Phoenix (NCC-65420-X) attempted to take on the mirror Jem'Hadar in those asteroids, the Sleri discovered themselves self aware enough to retaliate against both parties in space. When the shockwave of an exploding iso-star threatened the Sleri's lives, the Phoenix-X protected them with a barrier derived from transwarp technology. ("The Nega'Jem, Part I & II")