Cross references: Amphioxus Lamprey Asymmetry
Amphioxus Nervous System (NRC)
Full length PDF available online for free.
p.8 "the larval mouth develops initially on the left side and is innervated entirely by nerves emerging from the left side of the nerve cord (Lacalli et al. 1999)"
This is important to me since I'm very interested in what is known as "cerebral laterality" or "hemispheric specialization". Note that since the amphioxus nervous system crosses over much as ours does, these nerves which emerge from the left side of the nerve cord have their origin in the right side of the brain. This means that the right hemispheric specialization for emotion in we humans can be traced all the way back to the amphioxus.
A brain-Hatschek's pit connection in amphioxus (PubMed)
"In the adult lancelet, Branchiostoma belcheri, there is a lobe of the right ventral margin of the brain that extends around the right side of the notochord and makes contact with Hatschek's pit, which also is to the right of the midline. This structural system resembles the hypothalamo-adenohypophyseal system of vertebrates and appears to make possible seasonal nervous regulation of the release of gonadotropin."
See: Amphioxus Pituitary .
Establishment of left-right asymmetric innervation... (PubMed)
Only abstract available online. I haven't yet obtained the full article.
"Lancelets (amphioxus) exhibit a remarkable asymmetric development in the anterior body region, which is reflected in the peripheral nervous system even at adulthood. ... As the mouth expands and shifts posteriorly, the left fifth to ninth nerves join the left third and fourth in the innervation of the oral region. The left third to sixth nerves anastomose with the oral nerve ring, which encircles the mouth on the left side.
In the juveniles and adults, there are two nerve plexuses that run parallel to the margin of the oral hood. The innermost of these, the "inner oral-hood nerve plexus", is asymmetrically connected with the left third to fifth nerves on both sides. ... The velar nerve ring is also innervated asymmetrically by the left fourth and fifth nerves. From these observations, we suggest that ... the asymmetric innervation retained in adult lancelets is related to the early anastomosis of the left nerves with the oral nerve ring."