Fig. 4 in The morphology and fine structure of the Ordovician Cephalodiscus-like genus Melanostrophus

Fig. 4. Melanostrophus fokini Öpik, 1930; Upper Ordovician (Kukruse Stage, C β Ubja); ZPAL Pb 6/1. TEM micrographs. A, B. Transverse sec2 tions of the tube wall showing homogenous and fibrillar ultratructure. Abbreviations: f, fibril; h, homogenous material.