“Naked lungs,” nudibranchs: Undulant sea slugs, frilled and harlequin. They are hermaphrodites and cannibals. Male or female, mate or lunch. Permutations abound.

Imagine: you meet at San Francisco’s sea-themed Farallon restaurant, “a resemblance of a beautiful underwater fantasy.” Jellyfish pulse around you. Flanked by glowing columns of kelp, your date eyes you, sensing your signals, your orientations. If the dénouement goes well, maybe you’ll get nibbled—or more. If the night is a catastrophe, you walk away knowing you escaped demise. Sometimes it’s a bit of both—you’re missing tentacles, but you can’t wait to see them again.

Perhaps it is anthropomorphic of me to suppose my way into a nudibranch encounter. Anthropomorphism, that arrogance that imposes human thoughts and feelings upon animals, is surely a sin. But like most sins, I also think it reveals some truths.

Invertebrates, or as biologists call them, “inverts,” like the nudibranch are critters liberated from the constraints of a backbone. They offer a particularly rich resource for examining the limits of sex and sexuality. Consider the limpet, a snail-like hermaphrodite that undergoes sex change during its life. It is born sexless, then matures into a male at nine months. After a couple of years, he becomes female. These little conical beings, no bigger than poker chips, deliciously pervert and invert our human assumptions about bodies.

In general, we pretend sex is obvious, as if our chromosomes calculate our entire physiology. But as we’ve slowly come to realize—with the help of feminism, “queer theory,” and biology—sex is many processes that include X and Y chromosomes, hormones, gonads, internal sex structures, and external genitalia, as well as history, culture, environment, and variables still to be named. Some marine inverts “know” that sex is a process; know it as part of their way of life.

Which is not to call nudibranch or limpet reproduction “queer.” Sex change isn’t queer for these organisms; it’s their norm. Unlike some queer humans, they are not challenging sex, gender, and sexual conventions. Humans also change sexes, but oysters and humans change in vastly different biological contexts, specific to their environments and capacities.

The comparison is meant to defy sex determinism and essentialism, but could just as easily reinforce it. Books like Bruce Baghemihl’s Biological Exuberance (2000)—cited in the U.S. Supreme Court case Lawrence v. Texas as evidence that “homosexual behavior is natural”—and Joan Roughgarden’s Evolution’s Rainbow (2004) have turned to nonhuman sexual variations as a way to understand, and even legitimate, human sexual diversity. “Cold Cape Cod clams, ’gainst their wish, do it / Even lazy jellyfish do it,” sings Ella Fitzgerald, so why can’t we do it? Such comparisons elide differences among species and their environmental and evolutionary contexts.

So, what can we say about nudibranchs and people, when all such comparisons are dicey?

Consider Green Porno, Isabella Rossellini’s recent series of short films on animal sexual behavior. “If I were a snail,” says Rossellini to the camera in her “Snail” episode, “I could withdraw my entire body.” Dressed in a leotard, she curls into a large, constructed shell on a ribbon of slime. “I could hide both my vagina and my penis. I have both,” she continues, with a naughty smile. Then, we see her and another snail initiating courtship by stabbing each other with “love darts.” “Sadomasochism excites me,” she says, moaning with pleasure.

At first glance, Green Porno seems more problem than promise. However playful the video is, the habits of the snail are made salacious for us humans. The invert(ebrate) as pervert comes across as the same old problem of anthropomorphism. But Rossellini’s sighs of pleasure also open up parallels between our human fantasies and the life of the snail.

The snail, limpet, nudibranch, and even we humans evolve through our abilities to experience sensations and their limits. Charles Darwin teaches us that life needs variation to accommodate our ever-changing environment. Our differences as species are elaborated at the sensuous edge of our selves; we are defined by our abilities to sense and respond to the world around us. Pleasure and pain, attraction and repulsion: sensation is the engine of change. It is through our differences and our abilities to differentiate that life opens up to indeterminacy and potential.

There is no direct relationship between a nudibranch and me—not even when I, a woman who was a fag-identified male seduced a man who was a lesbian-identified female. We are now married “heterosexuals” living in a swing state. But the nudibranch’s particular sexuality emerges from the same fundament as mine: life proliferates difference. I’m a woman with a transsexual history, because transsexuality is part of my species’ potential—by which I mean the web of relationships that make us human, like culture, environment, imagination, communication, and physiology. Transsexuality is just one way of being human, of being a thread in the web.

While I am queer and the nudibranch is not, both our sexualities are permanently under revision, because life itself is changing. And all of us will respond and react to the environmental pressures that we humans have helped to create—polluted oceans and depleted resources—and those forces that none of us can control. Perhaps these stresses will prompt new kinships and surprising alternatives, or they might foretell catastrophe and demise. Or, more likely, both.