Spare parts

Hermit crab enjoying his lunch.

Shrimp pellets; Yum!

Hermit crabs, besides the chelipeds (pincers) that they use to grab and carry things, have three pairs of mouthparts, which they use to hold and manipulate their food. Here, two are plainly visible as the hermit holds onto his fresh shrimp pellet.

He seems to have lost at least one of his chelipeds, probably after an argument with a crab, or even another hermit. He'll do fine, though; hermits can use the legs to grab their food, too. They're not as efficient, but they'll do. And with the next molt, he'll have a new cheliped. The blue appendage on the left is the growing replacement; hermit blood is blue, and the skin on the new pincer is still thin.

Blue blood and dinner forks

My hermit crabs have come down with spring fever. Most of the larger males are courting; some trying to convince a female to allow herself to be carried, others, each clutching his chosen mate, sitting on high places, waiting for her to molt.

Hopeful parents, on top of the big abalone shell. Waiting.

And as always, there has been some competition for mates, a few tug-of-wars with the unfortunate female as rope, a couple of frantic chases, and, sadly, a few duels; pincers at a quarter inch. A smaller male was the loser in one of these battles, and limped away with two legs on one side, none on the other. And no pincers. I thought he would die, but he's tough.

He still gets around; slowly, dragging his over-sized shell behind him. He rests in the shadow of a kelp holdfast or in a tangle of eelgrass roots, out of the way of his more active neighbours. But his blue and orange flags still wave happily, he manages to find food and eat it, even without his hands.

What's more; twice I've seen him "flirting"; face to face with a female, trying to hold the lip of her shell in the customary fashion, without success, not having the required pincers. The girls were not impressed and soon wandered away.

There's hope for him; if he can hold out until the next time he molts, he will have grown back some of the missing limbs.

I've been keeping an eye on him, making sure food lands in his vicinity morning and evening, admiring his persistence.

I noticed a blackish spot on his maimed side. A lump, glossy blue-black, the blue-black of a mussel shell. A parasite? Or what? I kept watching, trying to get a photo or get a clear view with my hand lens, worrying.

With the extra light from the flash, the addition is deep blue.

I finally got close enough to see; it's a forming pincer arm, still coiled, still without movement, but with all the parts; joints and pincer tips, well formed. Hermit crab blood is blue, which may explain the colour.

The white ovals behind it are the stubs of the missing two legs.

The stub of one leg is clearer here.

How does a hermit crab, bereft of hands, manage to eat? This guy holds onto something solid with one back leg, drags over a chunk of food with the pointed tip of the second leg, and then uses his first set of mouthparts, or maxillipeds, to grab it and bring it to his mouth.

The first two maxillipeds serve as forks.

He's lucky to have three separate sets of maxillipeds; the inner two sets do the work of jaws. So he won't starve.

Say, "Ahhh!"

Crustaceans have the most confusing mouths of any critter I've seen; jammed full of hairs and grabbers and feelers and assorted crunchers, and always, always, always in motion. Sometimes a crab will face the camera and stop waving assorted appendages for a second or two; hermits almost never. So I was surprised and pleased when one of the big grainy hand hermits decided to show me his "tonsils".

"Aaaahhh!"

 Zooming in:

Thank you, big guy. But I'm glad I'm not your dentist!

Workaholic hair

Tonight I watched one of the large hermit crabs steal a partially-digested snail from the anemone's mouth, then dash away before his larger companions could snatch it from him. He ran, at top speed, the full length of the aquarium. Backwards.

I couldn't do that. Not without stumbling, not unless I had eyes in the back of my head.

In the morning, the hermits are quiescent, some apparently sleeping (with their eyes open) in the corners, some stacked on top of each other like sleepy kittens, some meditatively grooming their antennae, some picking at a morsel of seaweed or a barnacle. I drop the day's ration of shrimp pellets into the other end of the tank. The scene changes, even before the pellets have sunk to the tank floor; all the hermits are running, scrambling out from the bottom of a hermit pile, dropping from the seaweed. The crab appears from his hidey-hole behind the abalone shell, but he's already out-done by the hermits; they have collected their breakfast, and are hauling it out of reach. He has to mug a slower one for his meal.

How do they do that? They couldn't see the food; they barely had time to smell it, let alone identify and locate it.

Grainy hand hermit, waving assorted antennae and mouthparts.

Their senses are different than ours. Not better, not worse; just different. Their eyes are compound, on stalks, and arranged so that they look both forwards and backwards. One may be looking at me through the glass wall, but at the same time, he's watching his back, in case of a visit by the crab. Handy trait!

As for smell and taste, the hermit has all the bases covered. He has four antennae; the smaller pair, the antennules, is a sensitive "smeller". Besides that, his legs are covered with sensory hairs; he can smell things just by stepping on them. And this covers a deficiency in his sight. Although he can see backwards, he can't bend those stalks down, so he can't see under his own feet. Not a problem when you can smell the ground under you!

A hermit can identify, by smell, a useful snail shell buried in the sand; he can pick out the species that he likes best, also by smell or taste. The hairs on his legs and pincers are multipurpose sensors that also distinguish temperature, touch, and water current.

Do they hear? Yes; those four antennae do that. How well, I couldn't find out. (Should I play some music to mine, and see if they respond?)

Zooming in, to show facial detail.

And then there are those long, long antennae. In this hermit, they're orangey-red. They are feelers, the equivalent to our fingers. The shorter pair in between the eyes are called antennules. The hermit flicks them continuously, waving and spreading the hairs on the flagella (that blue "flag"), capturing scent and taste from the surrounding water.

In the photo above, two of the three pairs of mouthparts are visible. These are always difficult to see, since they're constantly moving. There is a lower pair, green with orange, hairy tips; these manipulate the food and move it into the mouth. Just above these are a set of long spines, also hairy. I can't see what's behind them.

I don't know if all these mouthparts are sensory organs. I would think so, but haven't found any real info.

The idea of hair in the mouth makes me shudder, but then, I'm not a hermit crab.