The biology of the heteromorph ammonites is not clear, but one certainty is that their uncoiled shells would have made these forms very poor swimmers.

Ancyloceratida varied widely in size, ranging from diminutive Ptychoceras, which was barely 3 cm (1.2 in) long, to Baculites and Diplomoceras, which could grow to 1–2 m (3.3–6.6 ft) in length.

Members of the genus Hamites were much larger but had a similar sort of shape, though the shafts were open so that the whole thing looked rather like a big paper clip.

Many of the earlier heteromorph forms had regularly coiled shells barely distinguishable from the homomorph ammonites (for example, the Lower Cretaceous genus Deshayesites).

The Late Cretaceous enjoyed the widest variety of heteromorphs, including the straight-shelled Baculites and Sciponoceras; the helically coiled Turrilites; and the bizarre Nipponites, which looked more like a ball of string than anything else.