Ammonoids were soft-bodied organisms with an external shell.
The Hildoceras bifrons shell is a flattened spiral shape with evolute whorls.
Internally the shell is divided up into chambers - each chamber would have been filled with gas to act as a buoyancy aid for the animal.
As ammonoids are extinct and soft body parts are rarely preserved, little is known about their way of life. However, some evidence suggests that they had an active predatory lifestyle, catching prey in their tentacle-like arms.
A complete adult macroconch varies between 95mm and 175mm diameter, whereas an adult microconch varies between 24mm and 41.5mm diameter.
Nekton is a free-swimming animals
Evolute and involute are geometrical terms relating to the shape of a curve
Lappets are spoon shaped extensions from the margin of the aperture
Arcuate is curved
Striae are fine lines of ornament
Ventro-lateral keels are ridges (keels) located on the sides of the venter
Tricarinate and bisulcate are two grooves separating the has three ridges (keels)of the venter.
Venter is the shell edge around the circumference