Fig. 2

Symbion americanus, free male. Anterior faces to the left in all aspects. aVentral view. The penis (arrow) lies inside the lumen (double arrowhead) of the penial pouch (pp). Long cilia compose the lateral sensoria (ls). b Close-up of the penial pouch of a specimen in ventral view. Note that the cuticle at the base of the penis (cb) is devoid of ridges. cDorsal view. dVentrolateral view. The frontal ciliated field (fc) covers the dorsal side in the anterior-most third of the male body. On the ventral side, a ciliated field (vc) spans from the anterior-most part of the body until the penial pouch