Sea Elephant

Image: Roger R. Seapy
Pterotrachea coronata

I don't know about you, but for me the only possible response here is "?!"

Can you imagine? There I am looking through the good, old Encyclopedia of Life, wondering if there might be some cool mollusc I've never heard of before, when I spot a... thing. At first I thought it was some sort of transparent squid, but then I realised it was a transparent... thing. A thing different from a squid. It was a Sea Elephant. A transparent Sea Elephant.

Oh. So... "Sea Elephant". That's some kind of transparent thing then is it? Apparently so...

Image: Roger R. Seapy
Pterotrachea hippocampus
There are about 5 species of Sea Elephant, all in the family Pterotracheidae

As it turns out, it's a sea snail. But it's one of those weird sea snails that swim around rather than slime their way across the seabed. It doesn't float on the surface like the Violet Sea Snail and it isn't closely related to the Sea Butterfly or Sea Angel. It's actually more closely related to Tritons, which do in fact slime their way across the seabed.

This is TOO cute! It's like a mermaid's terrier!

Sea Elephants have found a slightly different way of swimming. The slimy bottom of slugs and snails is known as the foot, and in Sea Butterflies and Sea Angels this grows out on the sides to form a pair of wings to sort of fly through the sea. In Sea Elephants, the whole foot is squished at the sides and flattened so it becomes one, big fin. As it flaps, the Sea Elephant swims upside-down. Or, since they're neutrally buoyant anyway, they can just relax and hover effortlessly in tropical and subtropical oceans across the world. Bliss!

Image: Roger R. Seapy
P. coronata is the biggest, reaching up to 33 cm (13 in) long

The rest of the body is cylindrical, almost entirely transparent and split into three parts: the proboscis, trunk and tail. There's no shell, since that would be heavy and non-transparent. It'd be completely at odds with the style they're going for here.

The trunk is the main body, but it's the proboscis which is the real trunk. By which I mean it's the elephant's trunk that earns them their name. I really have to hand it to them! We have sea cucumbers, sea moths, sea potatoes (I made that one up just now but it turns out it exists!), even seadragons, but I would never have thought we'd get a Sea Elephant!

Image: Roger R. Seapy
Pterotrachea scutata

A lot of the more ordinary sea snails have a proboscis, too. It's a long, flexible hosepipe that has all their mouthparts at the end in something called the buccal mass. In there is their pharynx, all the various glands they need and the radula, which is like a tough, toothy tongue for cutting into prey. In the Sea Elephant, the buccal mass is one of only three body parts which aren't transparent.

Image: Roger R. Seapy

Transparency is of course a great thing for creatures who swim in the middle of the sea, but, just as we saw with the Glass Octopus, guts pose a problem. It's just really difficult to hide away your intestines! When you try to hide them under transparent things, I mean.

Image: Roger R. Seapy
The visceral nucleus

The next best thing is to make them as tiny as possible, so Sea Elephants bunch up all their viscera into what's called the visceral nucleus. If you can't beat them, CRUSH them!

Image: Roger R. Seapy
Head showing eyes.
Ganglia are nerve bundles while the statolith is like a little ball which rolls around in a bigger ball so the Sea Elephant can tell up from down. You can see them here because of the incredible transparency.

The other thing they can't hide is their eyes. Sea Elephants have really good eyes! Some snails out there have simple eyes called ocelli, that can only distinguish light from dark. Others have pit eyes of varying complexity that can at least tell what direction a shadow is coming from. Sea Elephants, like some other snails, have lens eyes that can form actual images.

Image: Roger R. Seapy
Eye

And they look like little crystal balls!

Some Sea Elephants have a long filament near their tail

Among the most important images is FOOD. Sea Elephants hang out at the upper levels of the sea; some like to go right near the surface, while others prefer to stay at depths of at least 100 metres (330 feet). Some spend the day as deep as 300 m (985 ft) and rise up at night.

Wherever they are, looking up at the light of day with their snazzy, image-forming eyes allows them to discern the silhouettes of small fish, jellyfish and other consumables. When they spot something, they rush over to get it. Most Sea Elephants have a large, flattened tail to give them a burst of speed, then they can extend the proboscis to pluck their victim from the water. It must be pretty weird, seeing a pair of fancy, disembodied eyes racing toward you like that.

Image: Roger R. Seapy
Firoloida demarestia is a little different from the others.
It's the smallest at 4 cm (1.6 in) long, has a tiny tail and the female has a permanent egg string.

Something else they'd like to see every once in a while is a member of the opposite sex. And they really do have separate sexes; the males even have a little sucker on their swimming fin which the females lack. I don't know exactly how it's used, but I have little doubt that it's for when a mummy Sea Elephant and a daddy Sea Elephant love each other very much.

Image: WoRMS for SMEBD
Shell of a larval Sea Elephant

One species of Sea Elephant keeps all her eggs on an egg string which permanently dangles from her back end, even when she doesn't actually have eggs. In any case, when the eggs hatch the larval snails are rather more conservative than their parents; they still have shells! Only after undergoing metamorphosis will they unburden themselves of this load and disappear almost entirely. Just a pair of eyes, a mouth and some guts floating around the place. I always wondered what happens when The Invisible Man eats breakfast.