Joey Tata (Brent), Chuck Couch (Adam), Brent Davis (Corpsman)
For the first time, cast members exit the flying sub via the rear hatch. They walk directly from the cockpit to the outside, however the dimensions of the model show that there should be some other room in the back (engines or something).
From the book Science Fiction Television Series:
Joey Tata commented on the magnificent volcano set. He added that Irwin Allen cautioned him (as an actor prone to very animated movements) not to touch the rocks, as they were made of foam. In the scene where Chuck Couch falls in the lava, you can see his hand hit a rock, which sinks in. Allen, seeing this, screamed, "Did you see that? He touched the rock!" Joey Tata said, "So? Look at all the rubber rocks floating in the lava." Allen replied "You're not supposed to see those!"
Actor Brent Davis plays the corpsman who looks for the ship's doctor after Crane is hurt. Davis appeared on a number of Irwin Allen shows and often went uncredited (as is the case here). The one time he was credited was for the Lost in Space episode "Target Earth" as the mike officer. Ironically, his scenes were cut from the final print!
Joey Tata, a Fox contract player, was also in the first season episode "The Mist of Silence" as Farrell, the man who was dragged kicking and screaming to his death by firing squad. He would appear in "Deadly Amphibians." When Hedison took the dive, his lines and actions were given to Tata and Del Monroe (Kowalski), hence Tata's large role in the resolution of the episode. For whatever reason, Tata is unbilled in this episode.
Victor Jory is another legendary actor Irwin Allen hired as a guest on one of his shows. Jory also appeared on The Time Tunnel ("Pirates of Deadman's Island") and The Green Hornet ("The Frog is a Deadly Weapon"). One of his most famous roles is Jonas Wilkerson (the overseer) in Gone with the Wind.
Midway through the episode, Crane smacks his head and is absent for the rest of the show (in sickbay with a serious concussion). He also misses most of an upcoming episode ("Fatal Cargo"). It is possible that David Hedison needed some time off to film an appearance on the variety show The Hollywood Palace, where Hedison performed in a spoof of Voyage with host Milton Berle. At the end of the episode, after Crane is noted as being "Seriously Injured", he is shown in the control room chatting about the adventure with not a single mark on him. He must have a mutant healing factor.
This episode was chosen to open the season most likely because of the impressive sets of the interior of the volcano. There are new effects shots of the Flying Sub as it navigates in the lava.