Critters in the deep

Some of you might have noticed the exciting news last week that the third species of seadragon has been filmed in the wild for the first time. Others, not living in Australia might now go “Huh? 3rd species?” or even “Huh? Seadragon?”. Which is completely fine, they are very cryptic species and it makes me feel like I can teach people something new 😉 The special thing about this new critter is that it lives in deep water, so I figured it was time to look into what critters are to be found below where divers can go.


Ruby seadragon (Phyllopteryx dewysea) (Source: WA Museum)

Let’s start with this new seadragon species, the Ruby seadragon (Phyllopteryx dewysea). It was described in 2015 and is found only in deep waters in the south of Australia. It is a cousin of the Leafy and Weedy seadragons, but mostly differs from them in the fact that it lives a lot deeper: below 50m. Besides the very exciting fact that there is a third species, it is also very interesting to see how it differs from other seadragons. The Ruby seadragon is ruby red, which is a great colour to camouflage yourself in deeper water. Unlike its cousins, the deep species does not have any appendages (the fancy frills so typical for the other seadragons). The explanation is once again pretty simple, there is not enough light for plants to grow in the environment it lives in, so it does not need the frills to resemble plants and maximise its camouflage. Another difference is that this new species has a tail that can wrap around objects, which the other dragons do not have. Have a look at the Ruby dragon in the video below:

We will stay with the pipefish and seahorse family for more deep species. Pygymy seahorses are a favourite for many divers, but what is virtually unknown is that there are no less than 2 species of pygmy seahorses that have never been seen alive and only live in the deep! The Bullneck seahorse (Hippocampus minotaur) and Hippocampus paradoxus (does not have a common name yet) are very mysterious species which we literally know nothing about. The Bullneck seahorse is only known from a couple of individuals found below 60m while trawing the bottom. The other species was discovered at 100m also using bottom trawling, only 1 animal has ever been found. They are a bit bigger than the shallow water pygmy seahorses (4cm to 6cm) and might live on gorgonian seafans or on bryozoans. Both of the species have only been found in Australia, the Bullneck seahorse in the southeast, H. paradoxus in the southwest of the country.


Larger Pacific Striped Octopus (Source)

Octopus are amazing animals, not only because most of them look cool and are very intelligent, but also because they show some really interesting behaviour. Divers are used to seeing species like mimic octopus or coconut octopus on the sand in shallow water, but some species venture much, much deeper. Larger pacific striped octopus (LPSO) can be found all the way down to 300m. They live in the eastern Pacific Ocean, in places like Panama and Nicaragua. Despite being an extremely interesting species, the LPSO has still not been scientifically described. Unlike most other octopuses, this species seems to like living in groups, sometimes of up to 40 animals. LPSO are beautiful animals that behave differently from other octopus species. They mate “beak-to-beak”, where other octopuses seem to prefer mating from a distance, or mounting on top of each other. Unlike shallow water octopuses, the female LPSO does not stop mating after it lays its eggs. Instead they keep on laying new eggs and mate with other males for much longer. There is good news for octopus-enthusiasts, this species does not only live in the deep sea, it can sometimes live shallow enough for scuba divers to be able to reach them.


Details of the Larger Pacific Striped Octopus (Source: Caldwell et. al 2015)

It would not be possible to talk about deep critters and leave out frogfish. Most non-divers only know about the existence of deep-water frogfish (although they might call them anglerfish) and not about their shallow cousins. I guess the scene in Finding Nemo with the big-toothed, bioluminescent anglerfish has got something to do with that. But in case there is any doubt, the shallow water frogfish and deep-water anglerfish are related. They all belong to the order of the Lophiiformes. The deep-water species generally look quite scary, with large teeth, dark colours and beady little eyes. Which makes me love them even more 🙂 Two interesting adaptation for the deeper species: they often show bioluminescence (produce their own light) to attract prey, which shallow species don’t do (although they might use biofluorescence). Another thing some species do, is mate in a very peculiar way. The males are a lot smaller than the females, once they find each other (which is rare in the deep sea), the male will attach itself to the female with its jaws. Over time, the male and female fuse together, the male basically becoming a parasite that receives all its nutrients through the female. This has major drawbacks for the male as well, since it will slowly shrivel up and become not much more than a pair of gonads attached to the female, serving no other purpose but to provide semen when she is ready to mate. Life in the deep…it’s quite something.


A deep-sea anglerfish (Caulophryne pelagica) (Source: National History Museum

If anything, having a closer look at deep-water critters has made me very curious about what else is out there. Searching for those elusive pygmy seahorse is something that got me particularly interested. I might have to become a technical diver after all, just to go find the little guys.



2 thoughts on “Critters in the deep

  1. Pingback: Seahorse and pipefish collection | Critter Research

  2. Pingback: Fish nerds, critters, sharks and shirts | Critter Research

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