Per the ancient lore, part 40

compound eye of horseshoe crab limulus
It is Friday, which means it’s time once again for the Ancient Lore post – time flies, doesn’t it? This week it’s a selection from the Science/Miscellaneous folder, and so what you’re seeing here is the eye of a horseshoe crab.

Okay, that’s a bit misleading. First off, it’s not the eye of a horseshoe crab, but just the cornea, kinda, because this is from the molted exoskeleton, an empty shell from a juvenile found entangled in dead seaweed. Second, it’s one of the compound eyes, but horseshoe crabs have ten eyes, or really, a hell of a lot more, but we’ll just count the compound eyes as two because I’m too tired to count all of those little ommatidia right there and you don’t care anyway.

Now, if you know anything about horseshoe crabs, you know that they’re armored and spiky little bottom-dwellers that mostly scavenge, and their mouth is directly underneath their shell; so, not exactly pursuit hunters, and not exactly easy prey. Which raises the question of why they need so many eyes, when it would seem that they don’t actually need any. This might be like asking why anyone needs multiple homes or sports cars or Hummel figurines – they don’t need them so much as they have some neurosis about collecting them. The better answer, perhaps (probably not,) is that they’re actually arachnids (the horseshoe crabs I mean) and we all know how they are with eyes – why have two when you can have eight, you know? But curiously, while most spiders have both simple and complex eyes (you know, the kind with focusing lenses,) none that I know of have compound eyes like those of flying insects, so horseshoe crabs are definitely being optical hogs here. Most of their other eyes are simple, and dot the top of the shell, a few on the underside, and a selection along the tail. Because why have a blind tail? I mean, really…

And when the habits of horseshoe crabs have been studied, it appears that the primary uses of these eyes are for sex. I am forced by my own nature to surmise that horseshoe crabs must have a habit of saying, “Hey, my eyes are up here – and down here, and over here, and under here…” And now you’re wondering where a horseshoe crabs boobs are, aren’t you? You perv. Anyway, according to this article, even though the main eyes are unfocused compound jobbies, they still do a remarkable job of discerning details and contrast, at least if the computer simulation reflects any degree of accuracy. These are the kinds of rabbit-holes I find when I’m just looking to fill in some simple details for a post.

Anyway, don’t try to sneak up on a horseshoe crab, and don’t expect to get away with any sleight-of-hand tricks. And to provide a little more context and scale, I present this other image from the same time, my brother finding the crab and apparently sticking his fingers in its eyes…

juvenile horseshoe crab limulus molted exoskeleton
By the way, I have to point out that this is my 1,500th blog post; I would have liked to have done something a little more special for the occasion, but time and lack of new photos and this heinous schedule have all conspired against me. I took note of the 500th post, coincidentally another about an aquatic subject, but missed celebrating the 1,000th post, which is remarkably anticlimactic. Maybe I should simply stop drawing attention to these events.

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