A characteristic feature of lingual surface of the mandibular first premolar is:
Rudimentary lingual cusp
Mesial marginal ridge
Mesiolingual developmental groove
Lingual triangular ridge
A characteristic of the lingual surface of the mandibular first premolar is the mesiolingual developmental groove. This groove acts as a line of demarcation between the mesiobuccal lobe and the lingual lobe and extends into the mesial fossa of the occlusal surface.