#6033 - Chelicerates And Myriapods - Evolution of Invertebrates

Chelicerates and Myriapods Opiliones Also known as harvestmen. Commonly found in back gardens, but not all look like the classic form, some can be short and stubby. They generally only have one pair of eyes and do not produce silk (unlike spiders). They have an externally segmented abdomen and no pedicel connecting tagmata (cephalothorax and abdomen - all fused together). They are chelicerates. Opilione means shepherd. Estimated around 10,000 species but 6,00 known. Can be found at elevation of 4000metres. Nothing known about amazonion harvestmen. Most are omnivorous but some are carnivorous. (apparently can be kept alive on cappuccino mousse). Unlike spiders, they masticate their food (spiders inject digestive juices). They have XY sex determination and internal fertilisation (spiders don't, they have 'nuptial gift' on pedipalps. The harvestmen penis is an inversion of the ovipositor. The earliest fossil was found in the Rhynie chert dating from 400 million years ago and it shows the ovipositor of the female, where the male penis would be inserted. Solifugids Two pairs of chelicerae. They are not true spiders, and there are 1095 species. Also known as solpugida. Found in arid climates like deserts. Found in burrows. Named affectionately as camel spiders. Scorpions There are 1400 species and they floresce under UV light. It may be some sort of signalling. The pincers are modified pedipalps - appendage on rostral segments. 4 pairs of walking legs. Have chelicerae. Have careful mating dances. Like other members of chelicerae, have indirect fertilisation - the male makes the female sit on a spermatophore. Pair of lateral and median eyes - median detect shadow and movement above them lateral to the side. Segmentation - can look back at annelid worm pre-arthropodal structure. Vesicle of poison in sting. Amblypigi - whip scorpions There are 140 species of whip scorpions but they are not scorpions. No sting and harmless, but have an ovipositor. Their first pair of legs (pedipalps) are modified as sensors. Mating is as in scorpions - sit on spermatophore.