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Bohemian Behemoths: Kinks in the Animal Kingdom

by Paolo Marra-Biggs (He/Him)

The ocean is a wondrous place, where body forms are not as confined as they are on land. The ocean’s dense medium creates a relative weightlessness and gives animals the freedom in a three-dimensional space to evolve into various body shapes and sizes, allowing peculiarities like the largest mammals to inhabit the planet, glowing algae that collectively illuminate entire coastlines, and enormous, ominously floating jellyfish.

Colorful, horned creatures are linked by white extrusions
Nembrotha chamberlaini nudibranchs mating. (Photo credit: Nick Hope, Bubble Vision)

Along with the various body adaptations in form and function that marine animals have undergone throughout the millennia, the ways they interact with each other have evolved as well. And as the simplest and most important metric of success, arguably, is reproduction, the oceans’ critters have developed some seriously sensational ways of getting it on. There are numerous examples throughout the animal kingdom that have been “letting their freak flag fly” for epochs.

For example, there are many types of fishes that are very comfortable with gender fluidity, and no other species even bats an eye at it. The Bluebanded Goby (Lythrypnus dalli), a sociable fish that lives amongst many of its own species, has the ability to change its sex from male to female and back again, based on whatever candidates are available. Sex changes are fairly common in reef fishes, with most examples following the path of starting as female and becoming male with age and growth, a characteristic called sequential hermaphroditism.

Giant clams, the namesake of this blog post, is one of these sequential hermaphrodites. These bohemian behemoths are stationary as adults, so “finding” a mate is difficult. To combat this challenge, these bi-sexual bivalves are able to produce both eggs and sperm, releasing them freely into the water column and allowing the clams the chance to mate with each partner twice, swapping roles.

Close photo of small silver fish with its head pointed vertically upwards, surrounded by other silvery bodies, in shallow water
Multiple males compete to fertilize the eggs of a female Gulf Grunion (Leuresthes sardina) as she deposits them in the sand. (Photo Credit: Naomi Blinick)

There are also some strange, randy rituals observed in the animal kingdom. Gulf Grunions will swarm the beaches by the tens of thousands in the Gulf of California, just at the highest tide line, out of water and breath. There, in a seemingly suicidal fit of passion, as these fish fight slow suffocation, they and their mates do the dance of love. The females frantically wiggle their bodies, pointing up towards the sky, as they lay their eggs in the wet sand. Meanwhile multiple males simultaneously writhe around each female’s body like a living hula hoop, each attempting to fertilize the eggs as they are deposited. Quite the daring acrobatic scene (PBS Video here).

Regarding the Darwinist reason for existence, in some cases once an animal has accomplished their “duty,” they have little else to live for and are done with their corporeal state. These animals that die after mating are called semelparous reproducers. But they often don’t die right away. They instead go into a strange state of post-coital senescence.

Octopuses in this phase stop eating, have clumsy, undirected movements, lose their eyelids, and commonly grow white lesions across their bodies. This transformation occurs over months before they officially kick the bucket. However, prior to this walking zombie phase, these eight-armed huggers can be insatiable lovers, but not in the most romantic way. Cannibalism is commonly observed amongst these cephalopods, where the female (who is usually larger) will feast on the male after reproduction. In one instance, a female day octopus was observed to mate with a male 13 times, then proceeded to strangle and eat him. What’s stranger? The Blanket Octopus (Tremoctopus spp.) female is up to 10,000 times bigger than her counterpart. While the females are large and elegant, reaching up to 6 feet, the males remain at about the size of a bottle cap. Quite the dynamic duo!

A graphic illustrating the gradual weakening of an octopus going through stages of senescence, with a decline in cellular density, sensitivity to surroundings, and posture.
Illustration credit: Terry Dawson

Worms. Already, some readers may skip this section, as they are often regarded as uncharismatic critters that commonly elicit a squeamish reaction. Palolo worms are a type of ocean polychaete worm that spends most of its time burrowed in coral colonies, but once a year, during a full moon and a specific tidal phase, they all swarm to the surface to mate. However, they do it in a bizarre fashion. At the tail end of the mature worm is a body part called the epitoke, which is filled with sperm or egg, depending on the sex. These epitokes will split from the rest of the body but retain the ability to swim, or squirm, to intermix with the other fertile keisters. The mating scene is quite a spectacle, like a can of silly string exploded under water, with thousands of epitokes squiggling about (see it here). This mating event causes quite a commotion, as people gather around to collect these fecund fannies, which are considered a culinary delicacy in some countries.

Close-up photo of two bright yellow creatures curled toward each other, like commas, each with a pointed dart out one end
A pair of nudibranchs (Siphopteron quadrispinosum) engage in reciprocal copulation. Coming from the right side of the head, the penis is attempting insertion, while the penile stylets (“Love Darts”) dual. (Photo Credit: Rolanda Lange)

Further down the kinky wormhole, a marine biologist’s favorite flamboyant critter is the nudibranch or “naked-gill.” These are sea slugs, or essentially shell-less snails, and along with shedding their shells, their anatomy has changed quite a bit. There are far too many amazing adaptations in these critters to explore in this post, but you can read about them here. However, for some of these sea slugs, the way to copulate is via stabbing its hermaphroditic, hormone-filled “love dart” into the forehead of the other partner. The hormone is believed to stimulate the stabbed slug to lay as many eggs as possible. However, since producing eggs is more costly as an anatomical expenditure, these love-dart duels can last a while (up to an hour!), as the winner ultimately has less of an energetic investment of producing just sperm, giving them a better chance to live and love another day. Lazy lovers! What’s more, some of these nudibranch partially feast on their counter-parts post-copulation. A little snack to go!

Finally, a few fun fecund facts.

As the ocean is home to the largest animals that have ever existed on this planet (the great whales), one can imagine it is also home to the most well-endowed species in the animal kingdom. Right whales have been found to have testes weighing up to 1,000 kilograms. However, a much smaller critter takes the cake as the most “gifted” for its size: the biggest penis-to-body size ratio goes to the gooseneck barnacle, which, if it were the size of a human, would have a penis 50 ft long!

Marlin, the doting father in the Pixar favorite “Finding Nemo,” is an Ocellaris Clown Anemonefish, a species known for its ability to change sex. When a larger female dies, like Nemo’s mother does (spoiler alert), the smaller male partner will change sex to become a reproductive female. So Marlin, Nemo’s father, would neither have been a Marlin (the fish species) nor a male! See in this Beckman Institute video.

And what’s more, the sea anemone which Nemo and his family lived in is peculiar too! Many types of anemone are androgynous, and can reproduce sexually with another partner, or asexually with itself by splitting into two, each its own animal!

In Hawaiʻi and throughout the Pacific, cultures have long celebrated non-binary and gender fluid identities as well as embraced various sexual orientations, and we continue to celebrate and ensure the safety of the LGBTQIA+ community. We humans as a collective are long overdue for this acknowledgement to be widespread! Humans are not alone in the animal kingdom in expressing the many facets of gender identities and sexual orientation. In fact, it is more common than not to have some form of non-binary adaptation. From birds to slugs, lizards to monkeys, you can find gender-bending animals in every phylum. And as a single, cerebral species in the elaborate tree of life, we too aren’t as simple as we appear and should aim to protect all the diversity of this planet, no matter how they get ‘jiggy wit it’.

As my mom always told me, “Don’t yuck anyones yum, and let your freak flag fly.”

Paolo Marra-BiggsAbout the author: 

Paolo is an ocean enthusiast, marine biology graduate student at the Hawaiʻi Institute of Marine Biology, with a background in marine conservation and education. He aims to work with state and federal management agencies to better protect the ocean and its environmental resources.