Figure 4

Confocal projections of the phalloidin-labelled musculature of Maritigrella crozieri two-day post-hatching pelagic stage. Apical views (ventral up) of A) Apical complex (ac) of circular and coiled muscles above the orthogonal grid of body wall muscles, and B) optical sections below the apical complex showing mouth retractor muscle (mrm) and a pair of anterior-posterior parenchymal muscles (asterisk) extending from the apical complex to the mouth (m in C). A pair of dorso-ventral parenchymal muscles (arrow heads in B) extends from the dorsal lobe (dl) to the oral hood (oh). C) Ventral, D) lateral and E) dorsal view of orthogonal grid of body wall muscles, mouth retractor muscle (mrm) and oral hood muscles; longitudinal (arrowheads in C), oblique (double arrowhead in C) and circular (arrowheads in D). Prominent circular muscles include the anterior primary circular muscle (apcm), the posterior primary circular muscle (ppcm), and the lateral lobe circular muscle (llcm). Two thick muscle bands extend between the oral hood and dorsal lobe (double arrowheads in D & E), the endings branch obliquely across the lobes (double arrowhead in C) and interdigitate with endings from the opposing fiber. Primary longitudinal muscles (arrow heads in E), epidermal eye (ee). Roots of the apical and caudal cilia are visible in the epidermis (asterisks in C, D & E). (F) Dorsal view, optical sections inside of body wall musculature at focal plane of dorsoventral parenchymal muscles (arrowheads), three pairs in bilateral organisation lateral to the intestine (in). (G) Ventral view, single optical section showing many parenchymal muscles radiating from the posterior primary circular muscle (ppcm) laterally (arrow heads) and anteriorly (asterisk), concentric rings of mouth muscles (double arrow heads). (H) More ventral still, an optical section behind the ventral lobes shows the mouth retractor muscle (mrm) extending from the apical complex and a ring of muscle (double arrowheads) around the pharynx (ph). Scale bars 50 μm.