seta 13-I-VII

The seta with setae 10, 11 and 12 on segments I to VII comprising a transverse median or somewhat posterior group of ventral setae; seta 13 is the nearest of the group to the ventral longitudinal midline of abdominal segment II; in many taxa, it is the most developed (sometimes even stellate) of the four grouped ventral setae on at least the more posterior segments.