This post is the fourth 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.

Up until this point in this post sequence on mimicry in ocean ecosystems, there has been a focus on examples of animals that have evolved to strongly resemble another species, entirely and completely, in regards to appearance and behavior. But not every mimic goes for copying the whole shebang. Sometimes, just mimicking a specific body part of another creature is all you need to get the job done. Or maybe a tiny portion of your own body is sufficient to parrot the entire visage of a smaller species. I like to call this particular flavor of deception “fractional mimicry”, because instead of whole organisms mimicking other whole organisms, it is organisms mimicking other organisms that are in radically different size classes, necessitating evolutionarily ingenious use of specific regions of the body, or the resemblance of such regions. Fractional mimicry works through the broad manipulation of shape and color, and more importantly, the perception of shape and color in other organisms. I’ve already talked about a species that uses fractional mimicry earlier in this post series; the mimic octopus, which can use a subset of its tentacles to mimic a sea snake, or poke just its stalked peepers out of the sand to mimic a partially buried mantis shrimp. In the same blog post, I talk about a jawfish that is likely mimicking the tip of one of the tentacles of the mimic octopus, following the octopus closely as it moves across the ocean floor: this situation is an example of “fractional mimicry” as I’ve defined it, as the whole body of the fish is used to imitate a small portion of the entire octopus.

There isn’t any significant difference, from an evolutionary or general biological standpoint, between “fractional mimicry” and any other form of mimicry. To be honest, I just needed a good way to break up all of these posts. Grouping together species that share “fractional mimicry” or share the distinction of being fish mimicking invertebrates, or whatever, just makes my life easier. Sorry if that’s a bit of a disappointment.

So, let’s get to talking about “fractional mimics”; animals that achieve all the deception, but with half the work.

This fetching little fish is the comet (Calloplesiops altivelis), although due to its showy, expansive fins, it is also referred to as the “marine betta” (especially in the aquarium trade). It is found on tropical coral reefs across much of the Indo-Pacific, and shares its genus with one other less widely-known species. The comet is a type of longfin (family Plesiopidae), a group of small, predatory, vaguely grouper-like fish somewhat closely related to damselfishes (in regards to damselfish, think clownfish, like Nemo from Finding Nemo). They are also thought to be cleverly subtle mimics. ‘Of what?’, you may ask. A sensible, spotted handkerchief? A floating cutout of a Lite-Brite?

In reality, the likely model for the comet’s mimicry is a living critter, with a lot more in the way of bones, and eyes, and skin. And teeth. Lots and lots of teeth.

Those are some eely nice spots you got there! *nervous underwater laughter*

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