Ammonite Anatomy & Terms Kingdom Animalia Aptychus: pair of plates to close the aperture or possibly jaws (singular plate is called anaptychus). Phylum Mollusca Conch: one-piece shell of a mollusk. Class Cephalopoda Subclass Ammonoidea Heteromorph: ammonoid shell can be of any form except planispiral with whorls touching. Orders Agoniatitida, Ammonitida, Ceratitida, Clymeniida, Goniatitida, Prolecanitida Macroconch: larger form, usually female. Mollusk shells are made of aragonite and conchiolin a crystalline form Microconch: smaller form, usually male. of calcium carbonate. Nacreous: iridescent mother of pearl. Ornament: external portion of shell anatomy such as spines, striations, ribs, tubercles, bullae, clavi. Planispiral: coiling in one plane. Siphuncle: tube that is on the shell’s outer rim connecting the chambers of the phragmocone to the living chamber. Whorl: one full revolution of the shell, 360 degrees. Involute: whorls Evolute: whorls not overlapping giving small overlapping or little Flank: lateral wall of shell or compressed umbilicus. overlapping. also called whorl side. Phragmocone: Suture: where the septa intersect the outer portion of the shell. chambered portion Protoconch: Umbilicus: Lobe: suture line that Saddle: suture line that first chamber of shell composed external points away from the points towards the of the shell. of individual center aperture. aperture. chambers called depressed camerae (singular portion of is called camera). the shell. Goniatitic: usually 8 lobes The chambers are around the conch, typical separated by septa of Paleozoic ammonoids. (singular is septum). Ceratitic: lobes have saw Living chamber or body toothed appearance, typical chamber: portion of of Triassic ammonoids. the shell where the live organism occupied from the phragmocone to the aperture. Ammonitic: lobes and saddles Venter: outer rim Aperture: opening of fluted typical of Jurassic and of the shell, keel. body chamber. Cretaceous ammonoids. © Cynthia Cassell 2020.