The oral sensory organs in Bathochordaeus stygius (Tunicata Appendicularia) are unique in structure and homologous to the coronal organ

Table 2 Comparison of characteristics of the oral sensory organs (oso) of Bathochordaeus stygius with sensory structures around the mouth opening in Oikopleura dioica (highlighted in bold). See discussion for details

	Type of organ	Type of sensory cells	Apical cilia on sensory cells	Innervation
OSO	Compact organ	Secondary sensory cells	Present	2nd brain nerve, ramus ventralis
Coronal organ	Row of individual cells	Secondary sensory cells	Present	2nd brain nerve, ramus ventralis
Ventral organ	Compact organ	Secondary sensory cells	Present	1st brain nerve
Upper lip cells	Two individual cells	Secondary sensory cells	Absent	2nd brain nerve, ramus dorsalis

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