PDF] Sensory Biology of Whip Spiders (Arachnida, Amblypygi

Most unusual is the fact that by the giant interneurons are prey capture, fighting, and whip spiders walk only on six legs, not on eight as orientation, unlike "true" spiders do not possess silk ments. Authors Whip spiders belong to a small arachnid order (Amblypygi) Dr. RAINER F. FOELIX, Naturama, Postfach, CH-5001 Aarau. that is not well known. Their most conspicuous feature are Switzerland; rainer.foelix@ag.ch: the elongated, extremely thin front legs ("whips", or antenniDr. EILEEN A. HEBETS, Deptartment of Ecology and Evolutinary form legs). These are no longer used for walking but are moBiology, Univ. of Arizona, Tucson, AZ 85721 USA. dified extremities carrying various sense organs very much like the antennae of insects. Whereas hundreds of olfactory ~ e y words hairs are concentrated near the tip of each antenniform leg, Arachnids, Amblypygi, sensory biology, behavior large bristles (contact chemoreceptors) are evenly distributed over the entire antenniform leg. The sensory hairs of each antenniform leg contribute about 30,000 small sensory axons which proceed toward the central nervous system Introduction (CNS). The sensory fibers originating from the mechanoreceptive bristles make chemical synapses with a few giant Whip spiders even most zoologists have not heard interneurons in the periphery. The giant axons (10-20 pm in of these animals, and even fewer have ever seen one diameter) of these large interneurons transmit nerve impulses in nature. They are 6Lexotic" indeed: although whip spiwith a high velocity (6 to the CNS. The Purpose of this ders are true arachnids (Order Amblypygi) and closely 'fast pathway still needs to be determined. Originally it was thought that the fast giant axons would trigger quick escape related to web spiders (Araneae), they differ in several reactions, but this was not confirmed in physiological experiaspectsUnlike "true" spiders do not possess silk ments. However, other possible behaviors that may be aided glands or poison glands. Most unusual is the fact that by the giant interneurons are prey capture, fighting, and whip spiders walk only on six legs, not on eight as orientation. most other arachnids do. This is because their first what makes whip spiders unique is that both synapses and pair of legs are very thin (< 0.5 mm) and long (up to 30 giant neurons are located far out in the peripheral nervous cm!) and are held out above the ground. These elonsystem. In all other arthropods except for some arachnids synapses and giant fiber systems are always found inside the gated legs greatly insect CNS. never in the ~er i~hew. nae and correspondingly are equipped with thousands . . . Kurzfassung GeiOelspinnen gehBren zu einer klelnen, wenig bekannten Ordnung der Spinnentiere, den Amblypygi. Ihr auffallendstes Merkmal sind die stark verlangerten, extrem dunnen Vorderbeine ("GeiOeln"). Diese werden nicht mehr zum Laufen benutzt, sondern dienen Bhnlich wie die Antennen der lnsekten als Trager verschiedener Sinnesorgane. Wtihrend die GeiReispitze Hunderte von Geruchshaaren aufweist, ist die abrige GeiOel ziemlich gleichmassig mit Borstenhaaren (Kontaktchemorezeptoren) bestilckt. In jeder GeiBel ziehen ca 30.000 kleine sensorische NeWenfaSem zum Zentralnelvensystem (ZNS). Dabei werden die mechanorezeptiven Newenfasern uber chemische Synapsen auf einlge periphere Riesenlnterneurone aufgeschaltet; deren Riesenaxone (10-20 prn 0) leiten Nervenimpulse mlt groRer Geschwindigkeit (6 mls) zum ZNS. Wofur dieses Schnellleitsystem im Verhalten der Tiere einaesetzt wird, ist noch nicht aeklart die urs~riinaof sensory organs that perceive a variety of mechanical and chemical stimuli from their environment (BECK 1968, BECK et al. 1977, HOFER & BECK 1995). The six walking legs also possess sensory hairs (mechanoreceptors for touch and vibrations), but the antenniform first legs provide the main sensory input. Whip spiders deprived of those important first extremities can no longer locate or catch any prey, nor can they orient themselves in their environment (BECK & G ~ R K E 1974;

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