I know this because I dated a lobster in high school. I found out when I tried to get to third base, and there wasn't one. We tried other stuff, but take it from me; there is nothing fun about a "claw-job."
She dumped me after about three months. I was upset. I got over it with a marathon visit to Legal Seafood. I don't handle rejection well.
The lobster? She became valedictorian. Her speech was titled "Lobster Civil rights in the 21st century: Butter: Enemy Mine."
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Science fact
Lobsters have swimmerets. Small paired abdominal appendages that help with swimming and reproduction. And they carry and fertilize their eggs externally on these swimmerets.
This is a swimmeret:
I'll admit, it might look vaguely vaginal. Like the maw of virtually every science fiction movie monster ever. But trust me, it's not.
Helpfully,
Homemaker Man