Hemichordate Hormones

Cross references:   Hormones     Evolution of Hormones     Hemichordates     
Parazoa Hormones     Coelenterata Hormones   Coelenterata Neuropeptides    
Protochordate Hormones
Amphioxus Hormones   

Gonadotropin-releasing hormone        
Only abstract available online. 
Mulberry cells are epidermal gland cells bearing a long basal process resembling a neurite and are tentatively regarded as neurosecretory cells. They occur scattered through the ectoderm of the proboscis, collar, and anterior trunk regions of the acorn worms Saccoglossus, usually in association with concentrations of nervous tissue.  
    They contain secretion granules that appear from electron micrographs to be released to the exterior. The granules are immunoreactive with antisera raised against mammalian and salmon gonadotropin-releasing hormone (GnRH). Similar results were obtained with another enteropneust, Ptychodera bahamensis, using antisera raised against tunicate-1 and mammalian GnRH.
"This is the first report of the occurrence of GnRH in hemichordates, probably the most primitive group clearly belonging to the chordate lineage.  The physiological function of GnRH in enteropneusts is unknown, but an exocrine function appears more likely than an endocrine or neurotransmitter role.
My comments:   
    1.  Apparently
, the gonadotropin-releasing hormone (GnRH) may be exocrine, rather than endocrine, meaning that it is released into the surrounding environment rather than into the animal itself.  This suggests that GnRH was originally a pheromone and only became a hormone later in evolution. 
    2.  The wide dispersal of the Mulberry cells "
scattered through the ectoderm of the proboscis, collar, and anterior trunk" is in marked contrast to the very compact pituitary gland.  This wide dispersal of the Mulberry cells is similar to the wide dispersal of the nerves.     
    See:  Gonadotropin-Releasing Hormone (GnRH)   .