Bioluminescent predatory creatures that stalk Sylvia Tilly, Adira Tal and a group of Starfleet Academy cadets after their shuttle crashes on the icy moon Kokytos in 3190.
Tuscadian pyrosomes are large, luminous predators that are drawn to sources of energy. A crashed shuttle with its systems still running is therefore a beacon to them, and they will attack whatever they find near it.
They appear in the Discovery episode All Is Possible. Tilly agrees to lead what should be a routine team-building exercise for Academy cadets, with Adira along to help. A gamma-ray burst brings the shuttle down on Kokytos, killing the pilot and leaving the group out of contact, and the creatures soon begin circling the wreck.
The cadets, who come from worlds only recently reunited and distrust one another, have to cooperate to survive. Tilly gets them moving across the ice to higher ground to send a distress call, and draws the animals away herself until the USS Armstrong beams everyone out.