Fig. 4.

Richtersius coronifer s.s. (Richters, 1903) from the Billefjorden population, buccal apparatus seen in NCM. a Dorsal projection of the entire buccal apparatus. b Buccal crown, dorsal view c Buccal crown, ventral view. d Placoids, dorsal view. e Placoids ventral view. Filled arrows indicate the cuticular hook on the T-shaped apophysis, the empty arrow indicates the dorsal triangular apophysis, the filled indented arrowhead indicates the bulbous apophysis at the anterior end of the ventral lamina, the empty indented arrowhead indicates the ventral triangular apophysis, filled flat arrowheads indicate constrictions of macroplacoids, the empty flat arrowhead indicates dorsal spikes. Scale bars in μm