InterFIG 1: Structure of the buccal cavity.

A. Horizontal section through the buccal capsule of an adult animal. (TEM; inset shows the plane of section; anterior is top.) Various cell types (dotted lines on the right lip) occupy the lips, which enclose the buccal cavity. The outermost layer is hyp 4 (h4), which connects to hyp 3 (h3) at the anterior and body wall muscle (BWmu) at the interior. hyp 3, in turn, connects to hyp 2 (h2) and a sensillar socket cell (So). On the cavity side, hyp 1 ring (h1) is bordered by the anterior (aa) and posterior (pa) arcade rings. The posterior third of the cavity is enclosed by the pharyngeal epithelial cells (e1, e3). Pharyngeal muscles (pm1, pm2) are seen behind the cuticular flaps. The amphid sheath (Amsh), which wraps the amphid processes, is located between body muscle and the arcades. The buccal cavity is lined by a cuticle which is distinct from the body cuticle (bc). The prostom cuticle (pc) is underlain by arcade cells (aa, pa), mesostom cuticle (mc) by pharyngeal epithelial cells (e1, e3), and metastom and telostom cuticle (m-tc) by pharyngeal muscle cells (pm1, pm2) (Wright and Thomson, 1981; Albert and Riddle, 1988). A posterior arcade process is shown on the left side of the image in lime green . Bar, 1 μm. (Image source: [Hall] B156-7821.)
B. Representation of the buccal capsule in horizontal section (based on Dolinski et al., 1998). (Gray) Cuticle; (beige) hypodermis; (lime green) arcade cells; (purple) pharyngeal epithelium; (green and light green) pharynx muscle; (dark green) body wall muscle. (Dgo) Dorsal pharyngeal gland opening.
C. Close-up of the cheilostom and the junction between body cuticle and buccal cuticle from the same image as in A. The cheilostom groove (arrow) is lined with body cuticle (bc) secreted from anterior hypodermal cells and the arcade cuticle (ac) secreted from the anterior arcade. These two cuticles have different compositions. The anterior arcade makes an extremely thin cylinder of tissue at its anterior margin (arrowhead).

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