Explain SMBC — the wiki for Saturday Morning Breakfast Cereal

The Joke

The comic's caption reads: "At some point in the past a marine biologist was very proud of herself." A female scientist is shown excitedly telling a colleague, "This will be called the circalittoral zone. It's dominated by clams." The colleague looks unimpressed.

The humor comes from the word "circalittoral," which sounds like it contains the word "clitoral." The scientist is proudly naming an oceanic zone that is "dominated by clams" -- "clam" being a common slang term for female genitalia. So the entire statement reads as an elaborate, layered innuendo, even though it is technically correct marine biology terminology.

The Humor

The joke works on multiple levels. First, the "circalittoral zone" is a real oceanographic term referring to a region of the continental shelf below the infralittoral zone, and it genuinely can be dominated by bivalve communities. Second, the combination of a word resembling "clitoral" and the mention of "clams" creates an unavoidable double entendre. The scientist's visible pride and the colleague's weary expression suggest the naming was perhaps not entirely coincidental -- or at least that someone eventually noticed the unfortunate phrasing.

References

The circalittoral zone is a real term in marine biology, referring to the deeper part of the sublittoral (subtidal) zone on the continental shelf, typically below the depth where photosynthetic algae can grow. It is indeed often characterized by filter-feeding organisms such as bivalves (clams).