Peavinenemertes whiteleyi, new genus, new species, is described as a member of the order Heteronemertea. The general morphology appears to be most closely related to the genus Cerebratulina (family Cerebratulidae). The significant generic characteristics of the new genus include the following: a proboscis containing three sets of muscles (longitudinal, middle circular, and inner longitudinal) without muscle crosses; the absence of a connective tissue layer between the epidermis and the body wall outer longitudinal musculature; the rhynchocoel wall circular musculature not interwoven with body wall musculature; the absence of foregut somatic musculature and subepithelial gland cell layers; the lack of neurochord cells in the nervous system; the presence of a caudal cirrus; and the blood system in the foregut region developed into a vascular plexus. The specific characteristics recognized in this new genus are the following: proboscis insertion in the anterior region of the head; the accompaniment of the construction of foaming tissue forming the proboscis sheath; the rhynchodeal sphincter of the rhynchodeum derived from the pre-cerebral septum; the lack of the cephalic lacunae and cephalic vessels; the joining of the rhynchocoel diverticulum to the three longitudinal vessels in the blood vascular system; the presence of four large lacunae (dorso-and ventro-cerebral, post-cerebral, lateral, and vascular plexus); and the presence of the undulation of lateral edges on the body for swimming. These and other data important to the consideration of Heteronemertea are explained and discussed.
comparative nemertean morphology
eastern Pacific nemertean fauna