On the Fine Structure of Rastrognathia macrostoma gen. et sp.n. Placed in Rastrognathiidae fam.n. (Gnathostomulida)

Abstract

Rastrognathia macrostoma gen. et sp.n. is described as belonging to Rastrognathiidae fam.n. The ultrastructure is described, especially the nervous and digestive systems and the epidermal specializations. In the epidermis the single cilia belong to the choanocyte‐like cell type. An epidermal sensory cell with several cilia is described. The intraepithelial nervous system shows an orthogon pattern. Two ventral nerve trunks unite into a buccal ganglion. The jaws are secreted by the buccal epidermis. The endoderm consists of a single cell type. The food consists of bacteria. The mesodermal elements consist of six main longitudinal muscles.

New characters in the Gnathostomulid mouth parts revealed by scanning electron microscopy

“…The apophyses are compact and show much more similarity to the apophyses in the filospermoid taxa than to the other bursovaginoids discussed above. Together with the evident lack of large, caudally extending lamellae, as in Labidognathia and Tenuignathia, this suggests that Rastrognathia occupies a much more basal position in Gnathostomulida than suggested previously (see Kristensen and Nørrevang, 1977).…”

“…Jaws from three specimens from Kattegat, north of Zealand, Denmark, were investigated. Kristensen and Nørrevang (1977) and Sørensen (2000) give a detailed description of the jaws, but some further notes and corrections are added here. In the former descriptions, all paired parts of the articularium have been interpreted as lamellae symphysis (Kristensen and Nørrevang, 1977;Sørensen, 2000).…”

“…Kristensen and Nørrevang (1977) and Sørensen (2000) give a detailed description of the jaws, but some further notes and corrections are added here. In the former descriptions, all paired parts of the articularium have been interpreted as lamellae symphysis (Kristensen and Nørrevang, 1977;Sørensen, 2000). However, according to the terminology used in this study the term "lamella symphysis" should be restricted to the paired structures composed of longitudinally arranged rods that line the inner margins of the jaws (see Discussion, below).…”

“…No basal plate or jugum is present. Spermatozoa are small, rounded, and covered with microvilli (Kristensen and Nørrevang, 1977;Sørensen, 2000).…”

Gnathifera

“…The animals have a mouth opening that contains the pharyngeal bulb with the cuticular jaw structure. Gnathostomulids have a blind gut -some species possess a "temporal anus" (Knauss 1979 ) -an anterior brain, a ventral ganglion that is affi liated with the mouth, and one to three pairs of basiepithelial nerves (Kristensen and Nørrevang 1977 ;Müller and Sterrer 2004 ). …”