Diseases of chelicerates

Abstract

Chelicerates represent one of the oldest and second most speciose groups within the Phylum Arthropoda. Often referred to as ‘living fossils’, extant chelicerates inhabit terrestrial and aquatic ecosystems. Spiders, scorpions, ticks, and mites are usually mistaken for insects, just as horseshoe crabs are misidentified as crustaceans. The biological and commercial importance of chelicerates cannot be overstated; members represent vectors of devastating animal and plant diseases (acarids), wielders of poisons and venoms (arachnids), and critical for the detection of bacterial contaminants in pharmaceuticals (horseshoe crabs). For many of the chelicerates (e.g. pycnogonids), there is a knowledge deficit with respect to host-pathogen antibiosis and histopathological condition. From the available literature, the book lungs and book gills are critical sites of pathogen dissemination throughout the haemocoel. Recent data gathered using high throughput sequencing reveals spiders as rich sources of endosymbionts and pathobionts. More broadly, research efforts are focussed on integrated pest management strategies using acaropathogenic and araneogenous fungi for controlling terrestrial chelicerate pests. This chapter represents the first extensive review of the diseases and pathobiology of chelicerates in the context of their innate immune defences. Much information has been accrued from captive settings, such as scorpions from zoological collections and horseshoe crabs in aquaria.