On the original Star Trek, Captain Kirk (William Shatner) declared that space was the "final frontier". Apparently, the folks at Hanna-Barbera had other ideas, and in 1972, suggested that the seas represented the true final frontier. Sealab 2020 was part of NBC's "Terrific Ten" Saturday morning lineup, one of two freshman series from H-B (Roman Holidays was the other). Cartoonsintros uploaded the open to YouTube:
If the narrator's voice sounds familiar, it should. It's Ross Martin (ex-Wild Wild West), who voiced Dr. Paul Williams, the series' lead protagonist. Martin would also do some other work for H-B, culminating with the Robonic Stooges segment of Skatebirds just a few years later. Martin isn't the only prime-time player in the series' cast, though. Ron Pinkard, who was also appearing on Emergency! at the same time, was heard, along with Ann Jillian (a few years before It's A Living). Unfortunately, Sealab was a little ahead of its time, and was cancelled after 1 season. Apparently, viewers didn't like the idea of a weekly exploration of life under the sea, although Disney's Little Mermaid would change those opinions nearly 20 years later.
Cartoon Network, scouring its vaults, decided to "upgrade" Sealab, but at the expense of long-time cartoon fans. Sealab 2021 was a 15-minute [adult swim] series that poked fun at the original show, and sci-fi in general. The cut-&-paste, colorform-style animation was a turnoff, which is why you won't see a clip of it here. Better that the original series is treated with greater respect.