Mesmerizing Marine Mimics: Ichthyo-invisible

This post is the sixth in a six post series outlining the evolution of mimicry within the ocean realm. These posts detail various ways in which organisms may copy other organisms in appearance and behavior, and the evolutionary context for how these mimic-model pairings have come to be. The first entry in this series goes over some fundamental introductory concepts and definitions regarding mimicry in general.

Blending in with your surroundings to the point of near invisibility is a trick that gifts huge benefits.

I know that at least for me, there have been moments in my life where I wish I could have become functionally invisible to those around me….situations where just fading into the background, completely and utterly, would have provided me instantaneous relief. Like that time in high school basketball when I scored on the wrong basket. Or that time when I was 16 and had to get my palate extended prior to getting braces, and for more than a week, I walked around with a space between my two front teeth wide enough to steer a barge through. Or that time I chickened out in the middle of asking someone to senior prom, telling her that she could go with me if no one asked her by the time of the dance “or whatever” (which is both cowardly and implicitly insulting, good one, teenage me!).
….ok, you know what? How about high school, as a whole, being what I’m thinking of here then. The entirety of high school was a bit of nightmarish cringefest and if I had the ability to Hollow Man my ass out of the visible spectrum, I’d have jumped on that shit.

I was not so fortunate, but there are members of the animal kingdom that can vanish from sight, becoming indistinguishable from the backdrops of their habitats….and they have far better justifications for this power than dodging social embarrassment and minor psychological scarring.

This biological phenomenon – evolving an appearance and/or behaviors that make you very hard to detect within your environment – can be broken down into two main varieties. The first is simple camouflage. This is where texture, color patterning, shading, and other visual properties that an organism has make it blend in seamlessly with the uninteresting crap in its general vicinity; dirt, rocks, foliage, whatever. Camouflage makes critters’ bodily outlines disappear, and their image becomes disrupted and lost in a sea of unbroken similarity, but they remain…hidden in plain sight like one of those visages lurking beneath the surface of an ever-frustrating-as-fuck Magic Eye illusion. The purpose of camouflage is to completely destroy the “object detection” potential of a casual glance, allowing the sneaky bugger to sit tight, unnoticed.

The bride looks lovely! It’s a shame her bridesmaids never showed up though.

Sharing a lot of kinship with camouflage is “mimesis”, which is a variety of mimicry where an organism evolves to closely resemble a very specific benign environmental object to avoid detection. The difference between camouflage and mimesis is subtle, but nonetheless quite important….in the same way that saying “dinner was greatly enhanced by the presence of my favorite dish, Grandma, and an antique tablecloth” is basically harmless, but the minutely different “dinner was greatly enhanced by the presence of my favorite dish, Grandma and an antique tablecloth” will likely raise a few red flags.

The difference becomes a bit more apparent when you look at examples of each category. The famous peppered moths, when laying flat against a tree trunk, blend in expertly with the pattern and color of the bark. The spots and stripes of leopards and tigers, respectively, help break up their outlines, allowing them to slink slowly after prey, fading visually into the tall grasses and undergrowth of their tropical home. These are both camouflage at work.
In contrast, a grasshopper that mimics the color and shape quite specifically of a dead, crispy, brown leaf to keep off the radar of hungry predators is using mimesis. Stick insects are also mimetic, and imitate the shape and movements of plant twigs and leaves to keep from being noticed.

Essentially, if you are using camouflage, you fade in with the surface of a twig or branch. Or you are hard to see against a backdrop full of twigs and branches.
If you are using mimesis, you, as a whole creature, resemble the very shape of a twig or branch.

These are two closely related evolutionary strategies, but with slightly different executions. Camouflage and mimesis both allow organisms to hide from sight without literally hiding.

Pictured: Homer illustrating something that is effective, but neither camouflage nor mimesis.

Camouflage and mimesis (sometimes generally referred to together as “crypsis”; from the Greek ‘kryptos’, meaning ‘hidden’) is easily the most common form of mimicry in nature, both in terrestrial and marine environments. In the ocean, the number of examples are staggering. Crinoid shrimp virtually disappear when they crawl among the branches of their home feather star. Octopus (and many other cephalopods), with their exquisite active camouflage, can vanish in an instant into a mind-blowing variety of backgrounds, Peeta Mellark style, making them the world champions in the game of “Oh Shit! There’s My Ex! Hide and Avoid the Upcoming Uncomfortable Interaction!”. Numerous species of open-water fish use countershading (light colors on the belly, dark on the back) or reflective, shimmering scales to make them harder to place in their vast, blue, light-rich environment.

Since there are so many examples of marine crypsis to choose from, I’ll make it easy and do a skirting approach on a set of cryptic fish, particularly some of the more impressive ones. Some of these fish I’ve already talked about in earlier posts in this series. Frogfish, for example, use elaborate camouflage to dupe their unsuspecting prey. Outside of frogfish, there are two main groups of marine fish that have really pinned down the camouflage and mimesis thing.

The first are the Syngnathiformes, an order of fish that includes fairly widely-familiar groups like seahorses and pipefish. But seahorses and pipefish only represent a subset of the diversity of this order, and there are plenty of families of Syngnathiform fish full of bizarre representatives. The Syngnathiformes all share skinny, stretched-out bodies encased in bony rings, making their skeletons look like a cement Slinky. They also tend to have tiny mouths perpetually pulled out in a pucker. But don’t let their cute, tubed snoots fool you; the Syngnathiformes are a guild of the most skilled ambush predators under the waves, using their weird, ridiculously-shaped bodies as mimetic devices amongst seaweed and other vegetation, obscuring their presence and allowing them to slowly approach delicious morsels, sucking them up one after another. Seahorses and pipefishes in particular use a unique feeding mode called “elastic recoil” feeding, in which the muscles that rotate the head upwards remain contracted, but release at just the right moment, causing the head (and mouth) to swing upwards in a blinding uppercut…straight into an unwitting prey item.

Syngnathiformes contain some of the most hardcore hard-to-spot mimetic fish in the ocean, and one small family from the tropical Indo-Pacific, the ghost pipefishes (Solenostomidae)…named for their uncanny ability to “ghost” out of the realm of visibility, illustrates this best.

Here’s a pair of robust ghost pipefish (Solenostomus cyanopterus) looking so much like fragments of reddish seaweed that it, frankly, pisses me off:

Yes, these are fish. Somehow.

Think I’m bullshitting you? Have a look at this roughsnout ghost pipefish (Solenostomus paegnius), looking like that gross splinter of celery that’s been stuck underneath your fridge for a few weeks, all covered in dust bunnies and mold. But it’s definitely an actual fish. See, it totally has an eye and everything!

I propose a new common name: fuzzy jade ninja-fish

The harlequin ghost pipefish (Solenostomus paradoxus) adds a dash of Lewis Carroll hallucinatory flair to unbeatable seaweed-mimicry superpowers, resulting in an animal with body proportions that don’t seem possible, adorned in mescaline-inspired colors.

It looks like a letter in an alien alphabet that has come to life.

Ghost pipefish depart so dramatically from the standard fish body plan that half the time, it doesn’t seem possible that these are indeed fish and not little fragments of algae adrift along the sea floor. It doesn’t help that the deceptive little bastards take great care to move deliberately in the slow, nearly accidental-seeming fashion of seaward in the push and pull of the current, tens of yards below the surface.
I generally have a difficult time trusting any animal if the location of its butt cannot be easily determined in several seconds of cursory inspection. I can hardly even discern where the main axis of the body is on ghost pipefish, so just their continued existence kind of fucks me up.

What else are they trying to hide? You know, other than every physical feature that makes them recognizable as an animal.

The Syngnathiform mimetic madness doesn’t stop with the ghost pipefish. There are also the “shrimpfishes”, which belong to the family Centriscidae. These are small, silvery, fish with long, pointed beaks and stumpy, tapered bodies shaped, unsurprisingly, like a shrimp. They range across the tropical Indo-Pacific, and many species (like the razorfish, Aeoliscus, shown below) frequent shallow, inshore waters, typically in areas with plenty of seaweed and almost always in tight-knit schools.

Also, did I mention they swim with their faces pointed straight down? Like…completely vertical. As in, like a collection of mini-flagpoles.

Ugh, god, we get it: you can do a handstand. Big fuckin’ deal.

This isn’t because evolution accidentally rotated the shrimpfish an extra 90 degrees in the Photo Editor of Life. This habit of swimming skillfully in the horizontal plane, with the body tilted ass-skywards like the nose is tipped with lead, is intentional. At any point, the shrimpfish can straighten out and scoot along like any other self-respecting fish, facing the direction of travel….but for much of its life, it takes the inverted route, bobbing and dancing in concert with its little pack of like-oriented weirdos.

It’s thought that this parading and pitching around like a living video game graphics error is a means of mimicking the spines of sea urchins, which are common in roving herds that munch their way across the shrimpfish’s vegetation-rich home. Shrimpfish are commonly found aggregating among the long, black spines of urchins, their centrally striped flanks resembling the needle-sharp lances that they flit between, rapidly beating their tiny, spatula-shaped fins against the lurching surge to keep themselves erect and convincing.

Of course, no examination of the surreal inconspicuousness of the Syngnathiformes would be complete without mentioning the seadragons.

Seadragons are a type of pipefish (although their heft and body shape make them look like seahorses, which are different subfamily), and are only found along the cooler coastal regions of Australia. There are three species, divided into two genera; the single variety of leafy seadragon (Phycodurus) and two species of weedy seadragon (Phyllopteryx). They are a bit larger than just about all seahorse species, but the largest seadragon only reaches about the length of a human forearm. They swim slowly among the seaweed, snapping up tiny crustaceans as they rock and lethargically teeter along through their underwater forest habitat. So, being pretty normal by pipefish standards, they aren’t exactly the terrific, marine monstrosities their common name might suggest.

If this is what you were expecting, I’m sorry.

The “leafy” breed of seadragon, Phycodurus eques, ranges along the coastlines of Western and Southern Australia. It is covered from head to tail in large, elegant, green-yellow fleshy extensions that mimic the fronds and branches of the seaweed that it floats amongst. These remarkable, delicate lobes are all for decoration, however, and the leafy seadragon is entirely propelled by tiny, hardly visible, translucent fins up near its “head” and down along the tail. Since these fins’ constant beating is hard to observe, the seadragon appears to leisurely drift along, its body core still and stiff, powered solely by its own will.

A dragon that soars with no wings? Falkor is that you?!

Unsurprisingly, these raggedy little guys and their built-in ghillie suits are a popular attraction in aquariums around the world, and have become the marine emblem for the state of South Australia.

Their cousins, the weedy seadragons (Phyllopteryx), inhabit much of the same region and habitat. Weedy seadragons have much fewer camouflague skin lobes, making them looked like a freshly pruned version of their leafy counterparts. They are also darker and more variable in color, and the lobes more closely match the leaves and bladders of kelp than the thin branches of other types of seaweed. Weedy seadragons also manage to look even more alien and creepy than the leafy seadragons. Leafy seadragons at least look like seahorses that may have gone too crazy in regards to accessorizing, but weedy seadragons look nothing like their adorable seahorse brethren. Weedy seadragons, with their cartoonishly elongated snouts and crooked bodies, look like the seahorses’ sad, reclusive uncle with scoliosis that only comes around to borrow money for enigmatic reasons and to make unsettling comments about the underage butterflyfish next door. Weedy seadragons are what you get when Salvador Dali tries to create a depressed balloon animal.

*high-pitched wheeze of self-loathing*

Just this year, a second species of Phyllopteryx was discovered off the coast of Western Australia. It appears to occur in somewhat deeper water than the other two species of seadragon, and due to its rich red coloration, it has been dubbed the “ruby” seadragon.

The second group of fish that have mastered the art of the low-key existence are the Scorpaeniformes, a massive order of fish that includes everything from rockfish to sculpins to scorpionfishes (the last of which I addressed in an earlier post in this series). A large number of species in this order are equipped with venomous spines and/or top-notch ambush predators that hunker down on the sea floor and wait for prey to make the fatal mistake of swimming too close to their eatin’ end. The lie-in-wait hunting strategy is one that requires a great deal of patience, but also the ability to be completely inconspicuous. Because of this, many stationary ambush predators in this order have evolved camouflage to help them sink in with the visual environment.
The scorpionfishes (family Scorpaenidae) are the quintessential badasses at this usage of crypsis (with the exception of boldly patterned, active swimming forms like lionfish), and the level of diversity within this family is tremendous, contributed from literally hundreds of species.

One of my favorites in this group are the Scorpaenopsis scorpionfishes, which are found all over the warmer seas of the Indo-Pacific. It’s perhaps a blessing that these fish are so adept at staying out of sight, because with their upturned faces, made up mostly of a perpetually frowning, toad-like mouth and a pair of comparatively tiny eyes perched high on the head, and squat, brick-shaped bodies, scorpionfish are about as homely as a fish can get.

Now, imagine you’re a small fish on the reef playing the lifelong game of Spot the Scorpaenopsis, and the scene below encompasses your fishy field of vision…

It’s like “Where’s Waldo?”…if failing to find Waldo meant getting eaten alive

Chances are you won’t see the tasseled scorpionfish (Scorpaenopsis oxycephala) at all when you pass right over him, but he’ll see you. He’ll see you just damn fine….

Scorpaenopsis scorpionfish tend to go for the algae-covered/rocky substrate type of look, which, cool as it is, is outmatched by the concealment efforts of another genus of scorpionfish.

Meet Rhinopias, an arm of the scorpionfish family line that has converged heavily on the frogfish’s camo game:

That’s one grumpy clump of seaweed.

Scorpionfishes often aid the effectiveness of their disguises by positioning themselves in places of favorable topography. Lumpy forms that look like rocks that haven’t bathed in a while frequent silty or turf-algae rife areas with plenty of rocks. Frilly, colorful varieties seek out seaweed or coral that goes with their outfit. But what if you need to blend in when there’s nothing around you other than flat, dull sand?

The crocodilefish (Cymbacephalus beauforti) seems to have figured that one out. Crocodilefish are flatheads (family Platycephalidae), a group that is somewhat close kin to the scorpionfishes and found widely across the Indo-Pacific region. Crocodilefish in particular are all about shallow reef habitats, and rarely stray deeper than a dozen meters. While they are capable of hiding from prey in rockier habitats, they gravitate towards sandy, open areas, where they can lay out flat.

And I’m serious when I say flat. Crocodilefish look like a muskellunge in a vacuum-sealed storage package.

There, they are effective ambush predators, visually inseparable from the surrounding sand and pebbles. Unlike many scorpionfish and scorpionfish-adjacent fish like this, the crocodilefish is of significant enough heft that most fish on the reef have reason to worry about traversing over the submerged deserts this creature haunts. While larger species of flathead do exist, the crocodilefish routinely achieves about the size of a baguette.

It’s name of ‘crocodilefish’ is well-earned, not only because of its weirdly reptilian mug, but also its merciless appetite. Using the same blinding speed of other scorpaeniform ambush predators, the crocodilefish opens and extends its jaws so fast that it briefly creates a strong suction force, yanking prey down the inside of its long, long face well before the victim releases what’s happened.


Here lies the ‘tail end’ of the post series…

This post on mimesis and camouflage is the sixth and final entry in the marine mimicry post series, a collection of entries that delved into everything from toxic flatworms (and the diversity of mimics “inspired” by them), opportunistic fangblennies, and practically unbelievable carbon copy imitations that not only bridged species lines, but sometimes entire phyla.
Mimicry has evolved with numerous functions, and in multiple evolutionary contexts, in just about every major lineage found in our oceans. Whether it’s used to acquire food or gain protection, deception about one’s basic identity is one hell of a good way to get the job done.

Image credits: Intro scorpionfish, robust ghost pipefish, roughsnout ghost pipefish, harlequin ghost pipefish #1, harlequin ghost pipefish #2, shrimpfish, leafy seadragon, weedy seadragon, tasseled scorpionfish, Rhinopias, crocodilefish, crocodilefish with prey in mouth

© Jacob Buehler and “Shit You Didn’t Know About Biology”, 2012-2015. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Jacob Buehler and “Shit You Didn’t Know About Biology” with appropriate and specific direction to the original content.


1 thought on “Mesmerizing Marine Mimics: Ichthyo-invisible

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s