Siryn (born Theresa Cassidy) is a mutant with the ability to produce a very loud, high pitched scream.
Siryn is seen as one of Storm's students at the Museum.
She, along with other students, attended Professor X's funeral.
When the X-Mansion re-opens, she is seen giving Storm a hug before returning inside.
- Acoustikinesis - Siryn has the ability to scream at sonic levels. It was able to disorient the entire school.
- In the comics, Siryn is Banshee's daughter. However, Banshee is supposed to have died before 1973, making it impossible for the film version to be his daughter.