An adult macroconch has:
An adult microconch has similar characteristics to that of a macroconch but variations include:
Ammonoids were a successful and diverse marine group that originated from bactritid nautiloids.
Their closest living relatives are the coleoids (cuttlefish, squids and octopuses), as well as bearing a very close resemblance to the modern nautilus.
The earliest Hildoceratinae evolved from a Tenuicostatum Zone species of Protogrammoceras, and the genera Hildaites followed by Hildoceras became common throughout the Falciferum and Bifrons Zones.
Hildoceras bifrons shares some similarities with Hildoceras lusitanicum and Hildoceras laticosta but can easily be distinguished by its marked spiral groove.
Hilderoceras semipolitum is also similar but differs in being more involute, smoother and with reduced ribs.
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