Fig. 1

Morphology of the pharynx and mesenteries. a Adult polyp. b–d Polyps at rest; the pharyngeal ectoderm (green) is retracted inside the oral ectoderm (yellow). e–g Partial eversion of pharynx occurs during capture/handling of prey (Artemia sp., indicated by *). h–j Ingested prey passes through the mouth and pharynx and remains in contact with the ectoderm (white arrows) of the mesenteries during digestion; colored arrow indicates endoderm of mesenteries (pigmentation from consumption of Artemia). k Cnidocytes (black arrow) and gland cells (green arrow) are restricted to the ectoderm of the mesenteries. l The external ectoderm of the tentacles (Tn, orange) and oral region (Or, yellow) is continuous with the internal ectoderm of the pharynx (Ph, green) and mesenteries (Me, purple). c, d, f, g, k, l are DIC micrographs. d, g, l are false colored. e, h are oral views, the remaining images are lateral/oblique views. Dotted lines in d, g, k denote position of mesoglea. White arrowheads point to the mouth, black arrowheads denote transition from external to internal ectoderm. Double white lines in a, l denote the transition from pharynx to mesentery. White scale bars = 2.5 mm; black scale bars = 20 µm