Saturday, February 19, 2011

They’re Everywhere!: An Overabundance of Ophiuroids and the Mantis-Shrimp Conspiracy

I am an observant person. Not about some things, like whether my desk is a mess or someone’s flirting with me or the architecture of a house is Georgian—but about many things, in particular things zoological, I am quite perceptive. I notice hawks perched on high branches; I spot a fox resting by the creek; I see the still, golden eye of a frog just above the surface of an algae-laden pond.

Visits to the zoo, overall, don’t require a great deal of that talent, since pandas and flamingos and lions are, by and large, fairly easy to spot, even in the relatively ample space provided for them. But even the zoo’s enclosures can offer the opportunity to notice more.

This is particularly true in the invertebrate house, since some of the inhabitants (e.g. octopi and cuttlefish) are masters of camouflage and most tanks contain myriad tiny, unmentioned crustaceans and gastropods grazing on the glass or the pebbled bottom. I especially like examining the coral-reef-habitant aquarium, in part because it’s right next to the mantis shrimp’s tank and in part because it’s full of small creatures that go unremarked by the majority of visitors.

This past week I noticed something that I’d never seen before: baby ophiuroids!

This means nothing to you, right?

Ophiuroids are also known as “brittle stars,” and they’re related to, and look a lot like, starfish—but while starfish have very clearly star-like shapes, brittle stars have a central disk from which radiate long, snaky arms (hence “ophiuroid,” since “ophiuros,” or something like that, is “snake” in Greek).

[a sketch of a brittle star]

[a photo of their arms,
to give you an idea of their snakiness]

Brittle stars are pretty cool, because although they, like all echinoderms (starfish, sea urchins, sea cucumbers, etc.), lack brains and even heads, individuals of light-sensitive species each have the equivalent of a compound eye. I don’t know the science perfectly, but I believe that their dorsal arm plates function as little lenses that, when all added up, make something like a compound eye, allowing the brittle stars to “see” light. (For more accuracy and more details, visit the Aizenberg lab’s research webpage, where you can even read the article they published in Nature about it). –That’s not really relevant to what I noticed at the zoo, but it is really impressive.

Brittle stars, like most echinoderms (if not all of them—I’d have to check), are what are called “broadcast spawners.” This doesn’t mean that they use a loudspeaker or radio program to announce their interest in breeding; it means that they cast their gametes (eggs or sperm) upon the waters, letting the currents intermingle them and create fertilized eggs that develop into larvae and, eventually, young brittle stars. It doesn’t sound like a whole lot of fun, compared to many other means of reproduction, but I couldn’t say for sure, and the brittle stars aren’t talking.

—All this is just by means of introduction, and to say that there must have been quite a flurry of gamete-casting a while back, because the coral-reef tank is full of little tiny brittle stars—all hidden in crevices of rock so that only a couple of their little waving arms are visible. (Visible to someone with their nose practically against the glass, that is.) If you didn’t know what brittle stars looked like, you’d never guess you were seeing mini-ones.

[arrows indicate all the little arms]

[even one under an empty shell!]

[the size of an adult, for comparison]

It was a pretty thrilling discovery for me, and one I didn’t share—although I did do some stealth educating and pointed out the adult brittle stars, a hermit crab, snails, and the mantis shrimp to several visitors.

Speaking of the mantis shrimp, I got a few good views of it as well, though its habit of briefly emerging from and then diving back into its burrow doesn’t lend itself to great photos. But I’ve been curious for a week or so now about why a nearby tank, which had used to house an impressive display of tube-worms, now seemed to have a Secret Mantis Shrimp living in it. I thought of it as a Secret Mantis Shrimp (or SMS) because it was even more retiring than the display mantis shrimp and because the tank was poorly illuminated and had no label describing its inhabitant.

[the Secret Mantis Shrimp (SMS)]

Now, however, I have more reasons to designate it a Secret Mantis Shrimp, because the zoo volunteers either don’t know about it or pretend they don’t know about it. A boy peering into the tank exclaimed impatiently, “I can’t see what’s in here!” and the nearby volunteer told him, “That’s because there’s nothing in there.”

(It’s worth mentioning that this would be inaccurate even if the SMS weren’t resident: I've learned from painful personal experience during my research that a tank full of seawater will having things living in it whether you planned them or not. For example, in addition to the SMS, this tank has a few tiny anemones or hydroids growing in it as well as a quite beautiful little tube-worm.)

Another, different volunteer, who came by to tell me things I already knew about the overt mantis shrimp, also denied the existence of the SMS. Part of it is my own fault; perhaps the shyness of the SMS rubbed off on me, because instead of just asking, “Why is there another mantis shrimp hidden in that unlit tank?” I asked, “Is there another mantis shrimp in that tank over there?”

“No,” he said decisively, and—even though I had left an opening for that answer by my stupid question—I became annoyed. Unfortunately, he went away to feed the anemones before I could confront him with his (a) misinformation or (b) lie.

[okay, it's not a high-quality shot,
but it's still worlds better than
those supposed UFO pictures]

Thus I cannot say for certain that the SMS is part of a vast Mantis Shrimp Conspiracy—but I’ll say it anyway, and what’s more, I’ll crack it wide open (to hell with Wikileaks)! So when the papers and internet are all abuzz with news of the second, surprise mantis shrimp at the Zoo’s invertebrate house, remember—you heard it here first.

{A note: I do write all text and take all pictures. Please do not reproduce either without my permission.}

1 comment:

Anca said...

I just saw photos of dead brittle stars and tube worms, smothered by the oil from the BP disaster, at the bottom of the Gulf. It's a shame that we more and more depend on zoos as "preserves" for the nature that we kill.

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