Fig. 4

SEM images of the pleotelson in P. algicola. a Pleonite 5 and pleotelson, ventral view, with left uropod detached; *, anal opening; dotted circle indicates the presumed region from which left pleopod 5 has been evolutionarily lost. b, c Sagittal plane of pleotelson, showing glandular cavity (b) and opening of glandular duct (c); **, acinar gland. b′, c′ Enlargements of boxed areas in b and c, respectively; arrow and arrowhead indicate barrel-shaped and filament-like secretions, respectively. Abbreviations: A, anterior; D, dorsal; L, left. Scale bars: 100 μm for a–c; 5 μm for b′, c′