THR is reporting that actors Iain De Caestecker and Elizabeth Henstridge have been added to Joss Whedon's pilot for Marvel's S.H.I.E.L.D. Henstridge will play Agent Gemma Simmons and De Caestecker wil portray Agent Leo Fitz. The names and descriptions of these characters were released at the beginning of October, they're described as follows:

These two came through training together and still choose to spend most of their time in each other’s company. Their sibling-like relationship is reinforced by their shared nerd tendencies – she deals with biology and chemistry, he’s a whiz at the technical side of weaponry.

The pair join actress Ming-Na Wen as Agent Melinda May and Clark Gregg, who will reprise his role as Agent Phil Coulson.

Joss Whedon will direct the pilot and co-write it with his brother Jed Whedon and Maurissa Tancharoen. It's expected to begin shooting in January.

Marvel's S.H.I.E.L.D. will be executive produced by the Whedons, Maurissa Tancharoen, Jeffrey Bell and Jeph Loeb.

(Photo Credit: Lia Toby/WENN.com)