Joss Whedon and Marvel's TV adaptation of S.H.I.E.L.D. is still rounding up its cast. The newest additions to the series? According to The Hollywood Reporter, Elizabeth Henstridge and Iain De Caestecker have joined the cast, both as agents for the secret intelligence organization known to the Marvel universe as S.H.I.E.L.D.

Henstridge will portray Agent Gemma Simmons, who is described as somewhat of a "science whiz," and De Caestecker will portray "technology guru" Agent Leo Fitz. Both characters will reportedly be working closely together in the series, and spend most time either working or bickering with one another.

Whedon himself is set to co-write the pilot with his brother, Jed Whedon, and Jed's wife Maurissa Tancharoen. He may also direct the pilot for ABC Studios when that begins filming in January, schedule permitting.

RELATED: The 15 Hottest Female Fighters in Martial Arts Movies

[via The Hollywood Reporter]