ectocochleate cephalopod

{{Taxobox

| regnum = Animalia

| phylum = Mollusca

| classis = Cephalopoda

| fossil_range={{fossil range|late Cambrian|recent|ref={{cite book

| isbn= 0-632-06048-4

| author= Peter Boyle

| first2= Paul|last2= Rodhouse

| year= 2004

| publisher= Blackwell Pub.

| location= Ames, Iowa

| chapter=3: Origin and evolution

| doi = 10.1002/9780470995310.ch3

| title= Cephalopods : ecology and fisheries }}}}

}}

The ectocochleate (externally shelled){{cite book

| isbn= 0-632-06048-4

| author= Peter Boyle

| first2= Paul|last2= Rodhouse

| year= 2004

| publisher= Blackwell Pub.

| location= Ames, Iowa

| chapter=3: Origin and evolution

| doi = 10.1002/9780470995310.ch3

| title= Cephalopods : ecology and fisheries }} cephalopods are the oldest known representatives of their class, dating back to the Cambrian period. Their aragonitic shells are not prone to fossilisation.{{cite journal

| doi = 10.1111/j.1502-3931.1985.tb00710.x

| title = Taphonomy and ichnology of cephalopod shells in a Maastrichtian chalk from Western Australia

| year = 1985

| last = Henderson |first=ROBERT A.

| last2=MacNamara|first2=Kenneth J.

| journal = Lethaia

| volume = 18

| issue = 4

| pages = 305 }} They contain the modern Nautilus and many fossil forms including the ancient Ellesmerocerida and the ammonoids.