Fig. 7
Histology and identification of mucocartilage-adjacent tissues. Scale bar is approximately 250 μm, and yellow lines indicate the estimated field of view in each panel. White arrows correspond to mucocartilage, black arrowheads indicate basement membranes, white arrowheads indicate mucocartilage-adjacent tissues, and gray arrows indicate perichondrium. Panels B-G are all stained with Toluidine Blue. (A) Reference image for 40 dpf lamprey larva. (B) Mucocartilage of the oral hood. The adjacent cells correspond to the proliferative zone of mesenchyme, but no perichondrium is observed. (C) Mucocartilage of the subotic region. Perichondrial tissue can be observed surrounding the parachordal process. The adjacent tissue in mucocartilage is the flattened epithelium of the pharynx. (D) Mucocartilage of the internal and external velar bars. Perichondrium is found surrounding the trabecular processThe medial flank of the external velar bar indicates nucleated blood cells while the lateral flank corresponds to flattened epithelial cells. Both sides of the internal velar bar in this panel are surrounded by epithelium. (E,F,G) Mucocartilages of the ventromedial longitudinal bar, endostilic cartilage, and ventrolateral plate. The perichondrium of the hypobranchial bar can be identified in panel G. The presumptive perichondrium of the ventrolateral plate and endostilic cartilage indicate the body wall proper while the that of the ventromedial longitudinal bar corresponds to endothelial projections of the endostyle. Keywords: ec: endostilic cartilage; evb: external velar bar; ivb: internal velar bar; oh: oral hood; so: subotic mucocartilage; vlp: ventrolateral plate; vmlb: ventromedial longitudinal bar