Thursday, May 26, 2011

Elusive Arachnids

After years of looking and hoping I have finally encountered some Australian Amblypygi. This group of bizarre looking arachnids are known as ‘whip spiders’. They superficially resemble true spiders but are very different in many ways. Australia has a handful of species in the tropics, but they are neither common nor easy to find.

Charinus pescotti from Kuranda
Amblypygids are found throughout the world, primarily within tropical and subtropical habitats. Australian Amblypygids are relatively small compared to some of their overseas relatives. This species Charinus pescotti only grows to a body length of around 10mm, with a leg span of around 25mm. The giant African Euphrynichus amanica can attain a leg span of up to 400mm.

Amblypygids have two distinct body parts and four pairs of legs, so at a glance they are a little spider-like, but that is where the similarity ends. The abdomen is flattened and has 12 segments, and they lack spinnerets and cannot produce silk. The first pair of legs are antenniform; very long and delicate compared to the other legs, and extremely sensitive to chemical and vibrational cues.

The first pair of legs are antenniform and are important sensory tools.

One of the most striking features of these animals are the palps. They are raptorial; they have become adaptations to snatch and impale their prey with. The palps have rows of spines on the inner edges, and while not in use the palps are tucked up in front of the face giving them a fearsome appearance. The chelicerae (mouth parts) are fang-like and are similar to those of mygalomorph spiders, but Amblypygids lack venom. Prey, usually insects, is captured with a lighting fast strike using the palps. The animal is the drawn back to the front of the Amblypygid where the chelicerae begin to tear it open while digestive juices are expelled into the opening. The resultant semi-digested fluids are sucked back up in the same manner as spiders do.

The spiny raptorial palps are held in front of the face when not in use.

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