Figure 5
Simonsenia aveniformis in a series of SEM images illustrating stages of valve morphogenesis.
(A–C) External view of the valve formation stages. (A) Raphe canal is laid down along with the supporting braces which split into two transapical ribs to form the valve surface structure, note the striae forming areolae still not fully developed (black arrow), the distal and proximal valve margin is still not fused (arrowhead), white arrow marks the place where the brace joins the valve face and is divided into two ribs. (B) Close up of the valve apex with raphe canal supported by braces and the transapical striae areolae formed, note the valve margins are formed as continuous strips of silica (arrowhead). (C) Specimen from natural population in Guadiana River with well-developed and elevated raphe tube supported by braces (arrow), note the presence of the fenestrae (black arrowhead) and the piece of the girdle band with distinct perforations (white arrowhead). (D–G) Valve internal views. (D) Raphe canal formed (arrow), the fibulae grow from both sides of the canal forming hammer like structures (arrowhead) are not fully expressed yet. (E) Valve interior with more advanced development of fibulae, some hammer like structures connected to span the raphe canal (black arrowhead), the two arrows are marking more advanced development of fibulae but not joined the yet. (F) Valve interior with fused fibulae (arrowhead) and cylindrical structures of the initial portulae (arrow). (G) Complete valve interior with developed perforated fibulae (arrohead) and portulae (arrow head).
