FIG. 3. — Theonella ukrainica n. sp.; A, cross-section of a branch showing vertical canals, NHM ZN5D; B, choanosomal skeleton showing regular tetraclone desma with smooth rays and terminal articulation, NHM ZN5D; C, choanosomal skeleton composed of tightly packed and deformed tetraclones from subdermal region (surface to the top), NHM ZN5D; D, dermal surface showing dermalia developed as phyllotriaenes and discotriaenes; between them modified and tightly locked (infilling entirely the space between dermalia) outermost choanosomal tetraclone desma, NHM ZN10C; E, typical dermal phyllotriaenes as seen above choanosomal skeleton, NHM ZN10C; F, Dermal discotriaene with axial canals (eroded) visible, NHM ZN10C. Scale bars: A, 2 mm; B, D, E, 200 µm; C, 500 µm; F, 100 µm. All SEM photographs.