Breathing, or gas exchange, takes place in folded, accordion-pleated, tissue called booklungs
. Air enters and exits through the ventral side of the abdomen directly into the booklungs
, where respiration occurs.
Evidence for terrestriality in mesoscorpions was provided by demonstration of booklungs
in Pulmonoscorpius Jeram, 1994 from early Carboniferous strata of East Kirkton in Scotland (Jeram 1990, 1994).
Once a host is found, the planidium climbs on to the spider, migrates to the spider's abdomen, and cuts a small hole to enter the spider en route to the booklungs
(Schlinger 1987; see Nielsen et al.
: Folded, accordian-like respiratory organs where gas exchange takes place.
Spiderlings were covered with a fine mist and the compound was forced into the booklungs
. Spiderlings remained in the chamber for 1 min and were tested 24 h later.