The two cavities in the cephalic commissure unite dorsally, but ventrally open into the first somite of the trunk.
But the mouth remains as an inpushing of the wall of the first somite.
Ventral tentacular cirrus of second somite of a thin or foliaceous and asymmetrical form.
In fact, more or less complete “excalation” of the somite takes place.
The simple identification of somite with somite in Limulus and Scorpio seemed to be threatened by this discovery.
The appendages of the 2nd somite of the opisthosoma absent, rarely minute and bud-like (some Amblypygi), never pectiniform.
(d) The appendages of the third somite (second post-oral) are clawless oral papillae.
I, Coelom of the first somite which carries the antennae and is in front of the mouth.
P, Protocerebrum or foremost cerebral mass belonging to the first somite.
II, Coelom of the second somite which carries the mandibles (hence deuterognathous).
somite so·mite (sō'mīt')
A segmental mass of mesoderm in the vertebrate embryo, occurring in pairs along the notochord and developing into muscles and vertebrae.