Longodus (Long meaning long and odus meaning tooth) is an extinct genus of thelodont, placed in its own family^[1][2] – Longodidae – which existed in what is now Estonia during the Ludlow epoch of the upper Silurian period.^[3] The type and only species is Longodus acicularis.^[1][3] They are most noted for their long, needle-like scales, which run vertically along their trunk.

Longodus acicularis possessed narrow but elongated scales, approximately 0.5 mm to 1.0 mm in length, with a width to length ratio of up to 1:11. Their heads were almond shaped, connected to a medium trunk and short, distinctly forked tail. Scales contained ridges along the margins, creating a ripple like visual effect. They also possess lateral spines posterior to the crown.^[2] The scales on the crown are dentine based, covered by enameloid, while the scales of the base are acellular aspidin based.