By Amy Whetstone, Qualifications and Skills Officer at the Society of Biology
The yeti crab and axolotl are two bizarre but brilliant species that are rarely in the limelight, but I believe deserve to be. So broaden your animal lexicon and spread the word about these peculiar aquatic species, who have adapted to cope in the harsh and inhospitable conditions they inhabit.
Yeti crab, Kiwa hirsuta.
This pale eerie-looking crab is so named because of its long hairy arms. It has good reason, however, for its strange appearance, not least the inhospitable environment in which it lives. The yeti crab was first discovered in 2005 at a depth of over 2200 meters which explains it pale appearance; no sunlight penetrates this depth so there is no need for fancy colours. So deep in fact that it can only be reached by using an unmanned submersible.
The next remarkable feature of the yeti crab is that it lives in an ecosystem which derives its energy, not from the sun, but from the Earth itself. Yeti crabs are found living on hydrothermal vents and are thought to eat the bacteria that survive on minerals released. The crab doesn’t just wait around for some bacteria to come along but actively farms them instead. This is where the hairs or ‘setae’ come in. The setae are covered in the bacteria and to cultivate them the yeti crab performs a dance which involves waving its hairs about. This process is thought to cover bacteria in a mix of sulphurous minerals and encourage their growth, ready for the crab to consume.
Axolotl, Ambystoma mexicanum.
The axolotl, otherwise known as the water monster, is frozen in a state of development known as neoteny and never reaches the mature adult state, unlike their closest relative the tiger salamander. As a result the adults retain a number of larval features such as the characteristic external gills. The evolutionary explanation for this perhaps lies with the axolotl’s habitat, high altitude aquatic environments where food is occasionally limited. As they remain in the smaller larval form they require less food and can therefore survive the harsher conditions.
The axolotl can also regenerate its limbs, 
a trait known as autonomy. This feature is shared with many amphibians and reptiles alike and acts as a last line of defence against predators. Unfortunately for them they are now considered critically endangered as the lakes in Mexico City in which they originated either no longer exist or are diminishing.
So here’s to the yeti crab, dancing its way to success under the seas, and to the axolotl that never grows up. Harsh environments bring out the most fascinating of adaptations in species in the natural world.