Respiratory system of arachnids I: morphology of the respiratory system of Salticus scenicus and Euophrys lanigera (Arachnida, Araneae, Salticidae).

The book-lungs and the tracheal systems of two species of jumping spider, Salticus scenicus and Euophrys lanigera, were investigated using gross anatomical, light and electron microscopic methods. Both species possess well-developed book-lungs of similar size and tracheal systems with a basically similar branching pattern. The tracheal spiracle opens into a single atrium, where it gives rise to four thick 'tube tracheae', from which small secondary tube tracheae originate in groups. The secondary tracheae (diameter 1-5 mum) run parallel, without further branching, into the prosoma. In the opisthosoma, they lie ventrolaterally, where they contact muscles and internal organs. In the prosoma, the secondary tracheae may penetrate the gut epithelium and central nervous tissue. The structure of the tracheal walls is very similar to that of insects, consisting of a striated inner cuticular layer with taenidial structures and a surrounding outer hypodermal layer. The wall thickness appears similar in all secondary tracheae, indicating that lateral gas diffusion may be possible through the walls of all small tube tracheae.