Buccal capsule of Zeldia punctata (Nemata: Cephalobidae): an ultrastructural study

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Abstract
The ultrastructure of the buccal capsule of the microbivorous soil nematode Zeldia punctata demonstrates important differences and possible homologies with that of the nematode Caenorhabditis elegans. In Z. punctata the buccal capsule wall is separated into an anterior to posterior series of six cuticular rhabdions. The most anterior, rhabdion 1, the cheilorhabdion, is continuous with the body-wall cuticle and is produced by the adjacent syncytial hypodermis (=epidermis). Rhabdion 2 is underlain by a stack of two nonpharyngeal arcade synctyia and, in this respect, resembles the prorhabdion of C. elegans. Rhabdion 3 includes six electron-lucent rods and is surrounded by muscle designated ma, whereas rhabdions 4 and 5 are characterized by an electron-lucent marbling and each is surrounded by three muscles designated mb and mc, respectively. In Z. punctata the dorsal gland opens into the lumen of the buccal capsule near the base of rhabdion 5, whereas in C. elegans it occurs farther posteriorly, near the base of the buccal capsule. Rhabdion 6 is electron dense and is surrounded by the md muscles. The ma and mb muscles in Z. punctata are hypothesized as homologues of the epithelial cells e1 and e3 in C. elegans, but alternative testable hypotheses are also proposed.