Fig. 1

Overall morphology of the arm tip of A. kochii. (a, b) Scanning electron microscopy. (a) Low magnification view of the oral side. (b) Detailed view of the terminal pit. (c) Parasagittal semi-thin section. Toluidine blue. c—arm coelom; en—ectoneural neuroepithelium of the radial nerve cord; hn—hyponeural neuroepithelium of the radial nerve cord; pbe—epidermis of the terminal pit bottom; s—sphincter in the radial water-vascular canal; s\(_2\)–s\(_5\)—subterminal arm segments 2 thru 5; sp—arm spines; t—terminal segment; tf—tube foot; wvc—radial water-vascular canal