English: Detailed anatomy of Protocodium sinense and comparison with modern Codium. a NWULJG 10,034, SEM close-up of thallus surface, showing contacts between utricle tips. b–d NWULJG 10,026. b Tomographic close-up in cross section, showing utricles are tightly packed and clavate to cylindrical, with tips rounded and smooth. c Tomographic close-up in cross section, showing siphonous branching at base of utricles. Yellow solid arrows point to bifurcations of the main basal siphon. d Close-up of medullar siphons. e Diagrammatic reconstruction of Protocodium sinense. f SEM imaging of a cross section of an extant Codium fragile ssp. tomentosoides thallus (reproduced with permission from Jim Provan). Scale bars: a 20 μm, b 10 μm, c 50 μm, d 20 μm, f 500 μm