Fig. 4

a-b Virtual histological sections of Harmothoe imbricata, scale bars 1 mm. a – transverse section, b – sagittal section. c–d virtual histological sections of Eurythoe complanata, scale bars 1 mm. c – transverse section, d – sagittal section. e–l 3-d models of manually segmented body wall muscles, gut and ventral nerve cord (VNC). Dorsal longitudinal muscles shown in red, dorsolateral longitudinal muscles in orange, circular muscles in blue, VNC in yellow and intestine in green. e – Glycera alba, f – Goniada maculata, g – Hediste diversicolor, h – Nephtys hombergii, i – Nothria conchylega, j – Harmothoe imbricata, k – Amphinomidae sp. (intestine and VNC not shown), l – Eurythoe complanata. m – schematic reconstruction of Rollinschaeta myoplena, colour scheme as per E-L, with oblique muscles shown in dark blue. n – plot of segment number and body length for three extant amphinomid taxa and Rollinschaeta. Abbreviations: el – elytrae, dlm – dorsal longitudinal muscle, dllm – dorsolateral longitudinal muscle, vlm – ventral longitudinal muscle, vcm – ventral circular muscle, dcm – dorsal circular muscle, om – oblique muscle, phr – pharynx, jw – jaw, dci – dorsal cirrus, vci – ventral cirrus