Invertebrates are animals that have no backbone. (Actually, to be technically correct, they have no dorsal notochord, but I want this blog to be intellectually light weight, so let's say the first definition is okay.)
Some invertebrates have captured the popular imagination. There are childrens' films featuring ants and bees. There are no childrens' films that feature cute, talking digenean flukes. You might dress your kid in a T-shirt with a picture of a butterfly. You would not dress her in a shirt with a picture of a tapeworm. Or, for that matter, a nematode, a nemertean, or a nudibranch.
Pycogonids are related to spiders, but Incy Wincy pycogonid never climbed up the water spout. A vestimentiferan never flew away home to find her children missing and her house on fire.
Maybe this is because having your house on fire is a pretty normal state of affairs for vestimentiferans. These animals live around hydrothermal vents on the ocean floor. At great depths, molten rock released below the earth's surface causes hot water to flow up into the ocean.
Before 1977, no one knew vestimentiferans existed. Scientists who were conducting an oceanographic survey from a navy submarine unexpectedly discovered unfamiliar worm-like creatures living around vents at a depth of 2500 metres.
Vestimentiferans live inside a hard tube. They have no mouth or gut. Instead, they are filled with bacteria. The hydrothermal vents release sulphur, which the bacteria digest to produce energy. (This is highly unusual, as most living things have to obtain energy either from eating someone else or from photosynthesis.) The vestimentiferan can then digest the bacteria.
In the words of our normally serious and world-weary lecturer, they are 'easy to remember for the exam because they're the ones that look like a giant penis'. Giant is the right word. Vestimentiferans grow to be 2.5 metres long.
More deeply unpopular invertebrate friends to come!