All pink and shiny

In the sand at the bottom of my aquarium, there lives a worm. He's a shy critter, and I used to only see him when I cleaned the sand, sifting through it thoroughly. Even then, all I usually saw of him was his quickly disappearing curves. He moves fast, even in dense sand.

But he's been growing. The last time I caught him, he measured about 6 inches long; he can easily grow to four times that. And he's hungry. So hungry he's forgotten to be shy. When I drop shrimp pellets into the tank for the crabs and hermits, he comes out to get his share, quickly retreating into the sand once he's got a mouthful. But he comes back for more; it takes a lot of food for his long, fat body.

I tempted him with pellets right up against the glass.

Pileworm, aka clam worm. Probably Nereis brandti.

He's a segmented worm. Each segment has two sets of leafy "paddles" which help with movement, and also serve for respiration. On the head he has two fat palps and four sets of tentacles, two small antennae, a huge mouth, and four eyes. With all that sensory equipment, he responds instantly to any movement, or change in lighting. And he smells the food from far away, under the sand.

And his coat is shiny, pink, and iridescent. He glows!

Found a pellet, and opened that enormous mouth. One gulp, and it's gone.

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En la arena en el fondo de mi acuario, vive un anélido, un poliqueto Nereis. Es una criatura bastante tímida; acostumbraba verlo solamente cuando hacía una limpieza completa del tanque, removiendo y lavando la arena. Aún así, normalmente apenas lograba un vistazo mientras se enterraba con toda prisa. Hasta en arena apretada, se mueve rapidamente.

Pero ha estado creciendo. La última vez que lo saqué de la arena, medía más o menos 15 centímetros. (Puede crecer hasta cuatro veces ese tamaño.) Y tiene hambre. Tanta hambre le motiva a atreveserse a salir a la vista en busca de comida. Cuando les doy de comer a los cangrejos y ermitaños, que comen bolitas de camarón, el poliqueto las huele y sube a capturar su cena. Agarra una bolita, y se retira a su hoyo en la arena para tragarla, pero pronto sale a buscar más. Ese cuerpo largo y gordo requiere muchas calorías.

Es un anélido segmentado; en cada segmento del cuerpo lleva dos pares de patas en forma de hojas; estos le sirven para movilizarse, y además contienen su sistema respiratorio. En la cabeza lleva dos palpos, órganos de tacto, cuatro tentáculos, dos antenitas, cuatro ojos, y una boca enorme.

Y su piel es de un color rosa, brillosa, e iridiscente. ¡Resplandece!

Shell game, Part 2

(continuation of Shell game, Part 1)

The shell that the big female hermit had discarded (see Part 1) was too large. Too big for her, too big for her companion, who is slightly smaller than she is. I decided to remove it from the aquarium; it was in the way. I left it for the present in a bowl of water, to allow anything inspecting the inner reaches to leave.

A few hours later, I glanced at it, in passing, and saw the worm:

Red and white banded sea nymph, Cheilonereis cyclurus

I hadn't seen one like this before, but the pattern is quite distinctive; it took only a minute to find it in my Encyclopedia.

"This stunning red-and-white-banded worm has a special commensal relationship ... with large hermit crab species. Together they inhabit the shells of some large snail species, ... Seldom does this sea nymph emerge more than the length of its head, making detection of its presence difficult." 

Side view. The high "collar" around the head distinguishes it from other sea nymphs.

Googling for more information, I found only one good photo, a taxonomic record in the Encyclopedia of Life (with photo of long-dead worm) and WoRMS, and the name on various lists. One scientific article documents its relationship with hermit crabs in Alaska. It is found from Alaska to California, and on the far shore of the Pacific, in China and Japan.

But what does it eat? How does a big worm fit in a shell with a fat hermit? How does it get in there? How common is it? I found very few answers.

Tail end.

What do I know? It's a polychaete, a worm with a pair of paddle "feet" and several bristles on each body segment. It has four eyes (right-click the top photo). The "feet" on this worm are divided into two white paddles on either side.

Like other polychaetes, he sways back and forth along his length, keeping his space open, keeping the water moving.

Paddles (parapodia) and bristles (setae)

He belongs to the Nereid family. These have strong jaws and teeth. Some are carnivorous predators, while others eat algae or other vegetable matter. I tried to lure this one out of the shell with a piece of shrimp; he wasn't interested, even when the shrimp was in contact with his face. I gather that he's vegetarian.

About that relationship: it's called commensalism. The word comes from Latin, "cum mensa", meaning "with table", or sharing a table.

In ecology, commensalism is a class of relationship between two organisms where one organism benefits without affecting the other. (Wikipedia)

This brings up even more questions: Which one benefits, the hermit, or the worm? How do we know they don't both benefit? (This would be mutualism.)

Can the worm live in other places, like burrowing in the sand? Or must it live inside a shell? Does it do better if there's a hermit in the shell?

Does the shell provide shelter, or does the hermit provide food? Or, vice versa, does the worm help to remove the hermit's waste products? Or help with irrigation?

The hermit that moved out was one of the fattest I've ever seen. Was this because of some advantage the worm gave it?

Facebook has it right: it's complicated.

The worm has had the shell to himself now for two days. He is still there, still poking his head out at intervals. Other hermits have looked over the shell, and they keep rolling it about, but have not attempted to move in.

Of paddles and orgies

One of the great things about a blog is that it serves as an aide-memoire; what I saw, when, where; it's all there, and searchable. So I was able to review my experience with the big polychaetes.

I find that I brought home a pair, both under 4 inches long, from the White Rock beach, in the first week of October, last year. Digging through the sand, then, I found a worm that stretched out to 7 inches long.

It's been almost seven months since then. Those three have turned into eight, at least twice the size of the biggest one, back then, plus a few more 4-inch specimens.

I had narrowed the species down to Nereis, possibly vellixosa, which grows to about 6 inches. I'll have to revise that. I think, now, that they are Neries vixens, recently renamed Alitta virens, or possibly A. brandti, which is also common and virtually indistinguishable from vixens. Both of these, the Giant piling sea-nymph and the Giant clam worm, grow to at least a foot, like mine.

One thing that confused me is that the parapodia on these big worms are different from those on the smaller ones. Those are like pencil points with hair on the end; these are triangular paddles, with no hair visible.

Yesterday's worm, with non-hairy paddles.

Last October's worms, with hairy pencil points. The smaller ones I have now are like these.

A website from Wales reassured me that I was on the right track; their A. vixens, which they call King Ragworms, have paddles, although near the head end, the hairy points are still visible. (Look at the middle of the second worm for the paddles.)

I found the explanation in Kozloff. He writes, about N. vexillosa,

"... the sexually mature phase of this species is rather unlike the phase typical of mussel beds and bay habitats. The fleshy parapodia become expanded into paddlelike structures for swimming, and periodically during the summer the ripe males and females swarm at night near the surface. ... The worms do not survive long after their nocturnal orgy, during which they simply spew out their eggs or sperm through openings that develop in the body wall."

The Giants swarm, too. Kozloff says it's an "exciting spectacle.I can imagine; think of yesterday's video, but with dozens of worms in the open water, thrashing about in the moonlight.

So I've sent my critters out into the big world, just in time to !!PARTY!! I'll have to keep an eye on the few that I kept at home.

I found a couple of interesting head shots of these worms; interesting, if not exactly cute. PZ picked up one from an underwater image competition, back in 2006. The original site is no longer available, but the photos are still on Pharyngula. The third one down is Nereis.

And Ugly Overload has two face shots, from Alexander Semenov. This second link goes to his Flickr page; it's worth clicking over there to see the rest of his macro photos. Amazing and wonderful!

Worm in a coat of many colours

The tide was high Friday afternoon on the White Rock beach, and still coming in. In the few feet between the waves and the mounds of rotting seaweeds, Laurie started idly flipping rocks, looking for crabs. At this level, there's usually not much else.

Under the rocks just lying on the surface, there was nothing. Rocks embedded just a bit yielded tiny shore crabs and squirming, hopping mounds of blue-green amphipods.

"Smiley"

The slowpokes; the rest are long gone.

I turned over a rock that was buried just a bit deeper, and something pink slithered out of sight down a hole. I dug it out and dumped it on a rock; it was a worm, at first glance looking like an earthworm, but in the sunlight, it shimmered with blue, green and yellow highlights. Frilly legs on the side identified it as a polychaete.

Worm #1

Under another rock, we found a second worm, a smaller one. Turning its rock around for a better view, Laurie inadvertently broke a couple of rings off the tail. (This is important; you'll see why in a bit.)

The two polychaetes at home, in a soup bowl. The long one is just under 4 inches.

I photographed these as well as I could, given that they never, ever, stop moving. Then I dumped them into the aquarium with the rest of my critters. They disappeared into the sand at the bottom.

Later, sorting the photos, and attempting an identification, I was stymied by the lack of detail in the faces; these were Nereids, it seemed, but I couldn't be sure.

There was only one solution: I emptied all the water out of the aquarium, carefully removed rocks and shells and seaweeds, making sure I didn't squish any of the anemones. Crabs and hermits scuttled out of the way; the barnacles and snails shut down. They would be fine.

I ran my fingers gently through the sand, and exposed a worm. Hooray! I fished it out and dumped it in clean water. But wasn't it bigger than I remembered? Seemed so. Maybe my memory is going.

I found the second and added it to the bowl. But -- what was this? Its tail isn't broken!

And no, my memory is fine. This second one is Worm #1, the 4-inch one. Worm #2 is still in the sand. The other one has been living in my sand bed -- how long? And how did it get there?

This worm is over 7 inches long, stretched out. It's as squirmy and wriggly as the other two, but I was glad of this; with each twist, its colours changed; it's a multi-legged rainbow!

These photos are blurry, and don't do justice to the iridescence of the original, but will give an idea of the variety of colours:

Tail end of worm #2, on the rock in the sunshine. The red line is the main blood vessel, running from head to tail.

Worm #3, in a plastic container. Every movement sent shivers of blue down the spine.

Under more gentle light, the colours are muted, but the pink reflects in the water around.

And I got my head shots, more or less.

Yes, those are eyes, two large and two small, just above. The little "V" in front are antennae; on either side, shaped rather like a Tegenaria's fangs, are the jaws or palps. The four spikes on either side are cirri.

Side view of the head.

And the tail, with a cute little button at the end.

Looking at the head, I think I can identify it as a Nereis, probably vexillosa, known variously as the sea-nymph, mussel worm, sand-worm, piling worm, etc. It grows to about 15 cm, although some may reach up to 30. (One foot.) Kozloff (Seashore Life of Puget Sound) says it eats algae, tearing it with those heavy jaws; some websites tell me it's a "active predator" that feeds on soft-bodied animals. If it's been living in my tank for a while (and it must have; the only way it could have arrived would be as a tiny red worm in a pill-bottle of sand), then it hasn't been feasting on the other animals; they are all multiplying happily in there.

I found a page of a lab manual on dealing with Nereids; I read,

They are difficult to handle before they are completely relaxed.

No kidding!

.