Sunday 8 March 2015

Squat Lobster

Image: Tin-Yam Chan
They're not actually lobsters! Still squat, though.

Squat Lobsters do indeed look quite a lot like lobsters, albeit small, spindly ones. Your typical lobster is a large beefcake of a crustacean, with thick armour and massive claws...

Image: robinbcox
Squat Lobsters are smaller. The biggest are just under 10 cm (4 in) long. The smallest are less than 1 cm (0.4 in)!

Image: Lin, C.-W.
How do you even cup of tea with those things?
These measurements don't include the claws, which is important because some Squat Lobsters have ridiculously long claws which may be several times the length of their body.

It looks pretty awkward, not to mention creepy, but it seems to work well for them.

Image: Tin-Yam Chan
In the interest of balance, here's a much less spindly Squat Lobster. They got choices!
There are some 1,000 species of Squat Lobster in the world. A lot of them live in warm, Indo-Pacific reefs. No surprise there, that whole area is a marine paradise so long as you can avoid getting eaten by predators who are bigger than you. It's an even better paradise for them!

Squat Lobsters can also be found in colder waters, right up to the chill of Norway and Canada.

Image: NOAA
AND they can be found in the deep sea, where some species must surely be the most colourful thing for miles around.

Image: Moorea Biocode
Galathea pilosa is absurdly colourful. What a clown!
Many other Squat Lobsters are very colourful in their own right, too.

And then, of course, there are those famous Yeti Crabs that live near to hydrothermal vents. You might think nothing can be more opposite to paradise than life next to a chimney of boiling hot, poisonous fumes surrounded by freezing cold darkness, but Yeti Crabs appear to live lives of quiet abundance down there. That's partly because no-one else wants to have anything to do with that place.

Always remember: one way to become king of your domain is to find a really horrible domain.

Image: James Lynott
Long-clawed Squat Lobster (Munida rugosa) somehow manages to glare at us with its claws
Most Squat Lobsters live on the sea floor. They don't have the kind of thick armour real lobsters are blessed with so they frequently hide out in rocky crevices. Some Squat Lobsters can relax in their lair with only those freakishly long pincers sprawling out. That way they can catch food as it passes by without having to venture out in the open.

Image: Shane Anderson
A pelagic Squat Lobster
A few Squat Lobsters live completely different lives. They're pelagic! They use their fan-shaped tails to swim through the sea and spend all their time in the open ocean.

Other Squat Lobsters can swim at least a little bit when they need to, but they prefer to keep their fan-tails curled up under their body. That's part of why they look so squat!

Video: Andy Pepper

Like a lot of crustaceans, Squat Lobsters are not fussy eaters. Most will happily munch on any carrion or detritus they come across, as well as snap up whatever fish or other creatures they can catch in those gruesome pincers.

Some like to scrape their dinner off stones and the like.

Video: Eunjae In

Other adorable little darlings prefer to raise their claws and snatch at bits and bobs as they drift their way.

One exceedingly strange species feeds on wood. Wood! Wood that sank all the way down to the deep sea! I mean... those creatures that feed on nothing but sunken whale corpses are bad enough. Imagine having to wait around for trees in the deep sea! A tenuous existence, indeed.

So, after all that... what actually ARE Squat Lobsters, actually.

Image: zslamaj
What a beautiful home!
First of all, they're decapods. Just like proper crabs and proper lobsters. Decapod means "ten legs", and proper crabs and proper lobsters do indeed have ten legs. Two of those legs are big claws which might not be used for walking at all, but still.

However, if you look at Squat Lobsters you'll see that they don't appear to have ten legs. They appear to have a mere six walking legs and two claws, adding up to eight. What gives?

This is a common condition among a group of decapods known as Anomura. It includes coconut crabs, hermit crabs, porcelain crabs and several others. None of these so-called crabs are "true crabs" because... they all appear to have only six walking legs. But if you look very closely, you would see that they do in fact have another pair of legs, it's just that they're extremely small and kept hidden away under their armour.

Squat Lobsters use these miniature legs to keep themselves well groomed. It's particularly important that they keep those gills clean.

But Squat Lobsters throw one more spanner in the works.

For a long time, Squat Lobsters were treated as a single, large group of crustaceans. However, it turns out this is wrong. We already know that there are true crabs and then there are things like hermit crabs which look like crabs, but aren't really. Well, through careful physical examination and DNA analysis, it's now known that Squat Lobsters are in a similar situation. Not everything that looks like Squat Lobster is closely related.

Image: artist1066
So mysterious...
Thus, there are six families of Squat Lobster. Three of them belong to a group which also contains porcelain crabs, the other three are more closely related to hermit crabs than to the other Squat Lobsters. So now we have this weird situation where one bunch of lobster-likes are very closely related to a bunch of crab-likes, and another bunch of lobster-likes are related to another bunch of crab-likes

I wonder which one contains the "true Squat Lobsters"? Some day we'll have to say that such and such Squat Lobster isn't really a true lobster and isn't really a true Squat Lobster, either. Can't wait!


TexWisGirl said...

how can they not be cute with a name like that? :)

Crunchy said...

Galathea pilosa is just excessive. Seriously, dude. Stripey OR spotted. Pick one.

Esther said...

There are no true squat lobsters. Everything is a lie.

Joseph JG said...

@TexWisGirl: Ha! It really is such a pleasing name!

@Crunchy: I know! It has stripy claws and one of those stripes is pink with dark pink polka dots. MADNESS!

@Esther: D: The Squat Lobster of crisis!