Vampire sea spiders suck on prey

ABC Science Online



Weird spider-like creatures that live at the bottom of the ocean and use a 'straw' to suck on their prey are baffling scientists.



These sea spiders, some of which are blind, are defying scientific classification.



Marine zoologist Dr Claudia Arango of the Australian Museum in Sydney agrees they are arthropods, but which type?



She presented her research on these unusual and poorly understood animals recently at the Scientific Committee on Antarctic Research meeting in Hobart.



"They are very weird looking animals," says Arango.



For over 100 years, scientists have been puzzling over how exactly to classify sea spiders or pycnogonids.



They crawl along the bottom of the sea floor, sometimes more than 6000 to 7000 metres down, where they live in the dark, feeding on slow-moving soft-bodied sponges and sea slugs.



The creatures are segmented and have an exoskeleton, which makes them an arthropod, the same grouping as crustaceans, insects, centipedes and spiders.



But they also have a very strange collection of features, including a unique feeding structure.



"They have a proboscis that's like a straw that they insert into the animals and suck out the juices," says Arango.



Such features make it difficult to fit them into any of the known groups of arthropods.



"They look like spiders, but they are not real spiders," says Arango. "It's been very hard to place them in a position within the tree of life."



Arango has been studying the diversity and evolution of sea spiders.



She has been using DNA and morphology to construct a family tree, using 60 species of sea spiders from all over the world.





This Antarctic sea spider has a 70-centimetre leg span (Image: Claudia Arango)