I'm not an expert in functional paleontology, but it has been suggested that the specific shape of heteromorph ammonites could be related to hooking on to macrophytes or branched animals:
Examination of ribbing pattern and its resolution in various parts of
the living chamber in 11 species revealed that the ribs were less
developed and had some traces of wear on the inner surface of the
hooked chamber, being well developed both on the lateral and outer
lower parts. This could indicate that the adult animals were
semi-loosely hooked (Ancyloceras, Macroscaphites) or permanently
clipped (Scaphites, Hoploscaphites) onto either horizontal or upwardly
angled stipes of non-calcified algal macrophytes or branched animals.
Comparison of the adult mode of life with those of modern cephalopods
suggested that ammonites of the suborder Ancyloceratina had developed
a stationary brooding phase that could have several ecological
advantages over free-swimming monomorph ammonites.