Fig. 4

Musculature of the trunk of Pycnophyes kielensis. Micrographs obtained with a confocal laser scanning microscope of one specimen with introvert inverted. The musculature was stained with Alexa-488-labeled phalloidin and appears green. Cell nuclei where stained with DAPI and appear blue together with autofluorescence of the cuticle. a and f are maximum projections, b–e and g–i are transverse projection of the maximum projection shown in a from anterior to posterior. Numbers indicate segment number, the animals are oriented with the anterior end upwards, and the scale bar is the same for all micrographs. a Overview showing the discrete sets of dorsal and ventral longitudinal as well as dorsoventral muscles in segments 7–9 and the continuous muscle fibers running over segment borders in segments 1–6 (arrowheads). b Transverse section of the anterior end of the specimen with eight paired placid retractors. c Transverse section of segment one with dorsoventral muscles and lateral longitudinal muscle. d Transverse section of segment one with placid retractor muscles. e Transverse section of segment 1 close to segment 2 with attachment site of the ventral placid retractors to the cuticle. f Posterior part of the specimen with pachycycli as attachment points for the longitudinal musculature in segments 7–10. g Transverse section of segment 9 with dorsal longitudinal musculature, ventral longitudinal musculature, and dorsoventral musculature. h Transverse section of segment 10 with dorsoventral musculature. i Transverse section of segment 11 with lateral terminal spine muscles. arrowheads points where ventral longitudinal musculature runs over segment borders, dlm dorsal longitudinal muscle, dvm dorsoventral muscle, gm gut musculature, llr lateral longitudinal muscles, ltsm lateral terminal spine muscle, nph nephridia, pc pachycycli, plr placid retractors, vlm ventral longitudinal muscle