Xystonella clavata (Jörgensen 1924)

Xystonella clavata from the Bay of Villefranche on October 14 2013. Z-stack of images made using a 20x objective & DIC optics; lugol's-fixed specimen. described as variety of X. longicaudata by Jörgensen in 1924, raised to a species by Kofoid & Campbell (1929).