Musuem Missive #2 OR A Conchologist's Conch

Is anyone on this earth as behind the times as I am? Seriously! I get a fair amount of ribbing for the fact that I still listen to music that came out when I was in college (but seriously you guys, The Strokes are STILL relevant!). Frankly, this is not news to me. In high school I was also listening to music from the previous decade (The Cure transcends definition by a single era!).  

But I do feel like I should have at least half a clue about things in shells. 

WRONG! 

You guys all probably knew about this, but I was all like whaaaa?

Figure 1. Xenophora, the Conchologist of snails

That's right, do you need me to repeat it?

Figure 2. Xenophora pallidula. Le sigh. P.S. All these pictures are going to be from Hipstagram.
Sorry, I only had my phone and the room only had fluorescent lighting.

If your jaw hit the floor, or your hand hit your forehead - you are correct!

So this is a family of snails(1) called Xenophoridae (= "foreign carrying").  Hoarders, that's what they are. I saw them when I was with the PNWSC touring the Burke Museum's malacology collection (old news).

My fingers are literally doing the equivalent of sputtering on my keyboard - I have so many things in my head, none of them can get out effectively! Ok, ACTIVATE BULLETS!

• Why is this?
• Do individuals have different preferences? Species? Or is everything just collected randomly??
• Why is this?!
• OOOH! You could do a really cool exploration of community change over time for these habitats, just using museum and private collections of these shells and looking at what other species are attached! These are extensively collected species because they are such a curiosity. And I bet the collection records are pretty good!
• WHY is this?!

Ok, a literature search yielded basically nothing - so those of you looking for cool master's projects to do that involve warm water diving - YOU'RE WELCOME!

A little cruising around the internets yields several possibilities, and one certainty.

First, the certainty: Deep Sea News is on top of their business, and posted this a while ago (see the first paragraph).

Now the two possible explanations I've heard of so far for why this is a thing:

1. Behavioral defense
2. Mobility

Behavioral Defense

The defense idea goes like this: Snails make it harder for predators to eat them by increasing their size AND making their shells stronger without wasting energy making a lot of new shell. I buy the size argument more than the strength argument. Lots of aquatic things do this like Daphnia with their rad goth neck wear. This makes sense in many aquatic places where fish are the scariest predators because fish can typically only eat things they can fit their mouth around (gape limitation). But what about crabs? Crabs eat snails (as you are painfully aware of if you have been reading this blog), and probably won't find this shell expansion much of an obstacle(2).

Alternatively, it might be a camouflage in shallower, clearer parts of their habitat. See the video below of Xenophora conchillyophora habitat, and you decide.

To be able to say anything about this, it would be helpful to know what actually preys on this snail in real life (in addition to fascinated humans, of course). If its all fish, then this makes sense to me. Fish are also visual predators, so camouflage would also make sense. So let's just do some cool experiments you guys! Tether out some decorated and minimalist snails and lets see how they do!(3) 

Mobility

It is reported (here), and I admit I cannot personally vouch for this having not experienced it firsthand, that the habitat of these snails is very muddy. By adding easily available shell material in a spiral fashion they increase their shell circumference without having to increase body size. The shell then works like a snowshoe keeping the snail from sinking in the mud. 

I don't have a good intuitive evaluation of this notion (WHAAAT? No arm waving?! Are you feeling OK, Emily?!). OK fine: the logic seems a little shaky to me. Even most large snails are pretty good at navigating through and on top of mud using their foot as a snowshoe. It doesn't seem very necessary to spend so much energy attaching shells to use their shell as a snowshoe, because that means their foot, which is the part that they need to move around, can't get purchase. So how to they get out of a situation like that?

Either, way. SOMEONE DO SOME EXPERIMENTS ALREADY!

Also I bet you're ready for some more pictures by now!

Figure 3. The snail shell you see on the bottom is not the actual snail
featured here under all that debris, but it's just as large! Also check out the bottle cap (left).  

Figure 4. This one looks wave-swept. Actually, I wonder if you can say
anything about the flow environment looking at radial versus directional orientation of their collections?

• Also how? How do they attach it?

Again, no literature, but read this quote from a defunct geocites enthusiast website:

"Characteristically, the shell is covered with other shells, shell fragments, coral pieces, or stones that are attached or cemented with secretions from the animal. The shells are attached dead, although there is one account of a live kitten's paw being attached in an aquarium. All bivalves and bivalve pieces are attached inner side up and gastropods are usually attached with the aperture up. Once an object is selected, it is cleaned (as is the site of intended attachment), and then the object is rotated and fitted to the attachment site. This may take up to 1 1/2 hours. The piece is then held in place with the animal's foot, snout, and tentacle bases and glued into place. The Xenophora may then lay motionless for up to 10 hours, only rocking in place now and then, seemingly a check on the strength of its new attachment." (4)

10 hours?! That's a lot of time spent out of commission to glue a shell or bottlecap into place.  Must be worth it for some reason!

REFERENCES & MISCELLANY:

(1) You will recall from your pneumonic that (F)amily is above "Good Spaghetti"

(2) In fact it might make it easier for them to manipulate by giving them little claw-holds, rounder shells are harder to just out and out crush (Bourdeau 2009 Ecology).

(3) To anyone who actually wants to do this, I am an expert at tethering snails - I have tethered literally hundreds in the last two years. And I have a valid passport and drivers license, just sayin'.

(4) Zymoglyphic took this from a now-defunct (shocking) geocites enthusiast page.