Yes. A fish with a transparent head. Brilliant. It’s called the pacific barreleye. What a funny looking little bugger. The dark blobs at the front of his greenhouse of a head are actually his equivalent of nostrils. The eyes are the greenish blobs inside the glass cage. Barreleyes are also called spook fish.
The barrel reference is from the slightly tubular shape of their eyes. They hypothesise that he (or she) swivels them bad boys around in the darkness of the deep, scanning for silhouettes of prey above. There’s a few types of barrel fish, and it’s the pacific barrel fish that features in the picture above and the video below.
They tend to hang about fairly deep in the seas, on the border between the pitch black depths and the dim light from the surface above. Their eye has a particularly large lens and its retina has no cone cells but a surprisingly high number of rod cells and rhodopsin – the “visual purple” pigment. It’s thought that the transparent dome helps the eyes collect even more light and also defend the sensitive barrel shaped eyes from the nematocyst (stinging cells) of the siphonophores (more on them later) from which it’s believed the naughty barreleye steals food.
The javelin spookfish (cool name btw) is the largest of the barreleyes, clocking up a full 50cm in length and chilling out at about 600m below the choppy surface of the Pacific and Atlantic oceans, here he is:
This is footage of the spooky pacific barreleye chilling out and about. It’s the first footage of this species taken whilst it’s still alive with it’s dome in one piece. Others have been dragged to the surface, and even those that have still been alive haven’t had their dome intact. So this is rare:
As for the siphonophores, the critters that the barreleye loots for food, these are strange beasts indeed and can grow up to 40m in length. Rather than being a single organism, they are an intertwined colony of individuals, drag-netting the seas for fodder. The most famous of these is the Portuguese Man O’War.
Portuguese Man O’War are often mistaken for jellyfish because of their appearance and sting, but in fact, they are a city of mini-beasts functioning as one. Siphonphores are on the border between single cell and multicellular life. Each individual zooid or medusoid that makes up the ‘body’ of these beasts could not survive independently, and each one is specialized and acts interdependently, very like the cells in higher animals. Siphonphores commonly exude bioluminescence to attract fish towards them, then specialised stinging cells paralyse their victim and other types of cells take up the job of consuming the quarry.
Here are some beautiful plates created by Ernst Haeckel in 1904 depicting some of their variation:
They’re incredible pictures aren’t they? That bottom one would be a pretty epic wallpaper design, if a little intense. Below are a couple of videos I found of these mysterious quirks:
And lastly, here’s a selection of clips from various dives courtesy of siphonophores.org and I recommend checking their site out if this has whet your whistle.