Fig. 1

Ultrastructure of the excretory ducts of Chimaericola leptogaster (a–f) and Calicotyle affinis (g–j). a Small excretory duct at a short distance from terminal cell. b Epithelial lining of the collecting duct; note surface lamellae and cilia of lateral flame. c Epithelial wall of the main excretory duct showing inclusions within its lumen; note a thick layer of extracellular matrix supporting epithelial cytoplasm. Insert: luminal inclusions (scale-bar: 1 µm). d Collecting duct; note basally located nucleus. e, f Epithelial wall of the collecting ducts showing invaginations of the basal membrane and septate junction. g Epithelial cytoplasm of the terminal portion of the main excretory duct showing wide invaginations of the basal membrane filled with extracellular matrix; note thick layer of extracellular matrix and muscle fibres around it. h Basally located nucleus of the collecting duct; note invaginations of the plasma membrane into perinuclear cytoplasm. j Epithelial wall of the main excretory duct; note surface lamellae, cilium of lateral flame, thick layer of the extracellular matrix. Abbreviations: bb, basal body of the cilium; c, cilium; ca, cilium axoneme; dl, duct lumen; ec, epithelial cytoplasm; em, extracellular matrix; fr, fibrous rootlet; i, invaginations of the basal membrane; lin, luminal inclusions; lm, lamellae; m, mitochondrion; mf, muscle fibres; n, nucleus; pc, perinuclear cytoplasm; sj, septate junction; ss, smooth luminal surface; v, vesicles