Figure 3.

The axochord in spiralians. The tree follows 21. A: Trochozoa. Annelid after 14, molluscs after 40, brachiopod after 43 (and personal communication of Dr. Andreas Altenburger), nemertean after 46. B: Cycliophora, Rouphozoa and Gnathifera. Cycliophoran after 39, gastrotrich after 54, rotifer after 49 (note that the schematic in this paper presents the paired ventromedian fibers slightly more distant than they are in the actual specimen; Dr. Martin V. Sørensen, personal communication), gnathostomulid after 52, micrognathozoan after 53. Colors are as in Fig. 2A, and the paramedian muscle of micrognathozoans is orange.