Knightoconus
Extinct genus of molluscs
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Knightoconus antarcticus is an extinct species of fossil monoplacophoran from the Cambrian Minaret Formation of Antarctica.[2] It is thought to represent an ancestor to the cephalopods. It had a chambered conical shell, but lacked a siphuncle.[3]
| Knightoconus Temporal range: Dresbachian ~ | |
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| Artistic reconstruction of Knightoconus antarcticus | |
Scientific classification  | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Monoplacophora |
| Order: | †Kirengellida |
| Family: | †Hypseloconidae |
| Genus: | †Knightoconus Yochelson et al., 1973[2] |
| Species: | †K. antarcticus |
| Binomial name | |
| †Knightoconus antarcticus Yochelson et al., 1973[2] | |
Taxonomic debate
The absence of a siphuncle in K. antarcticus has been taken as evidence against its being an ancestor of cephalopods, as factors that would allow a siphuncle to penetrate preexisting septal chambers remain unknown. The prevailing argument suggests that a strand of tissue remained attached to the previous septum as the mollusc moved forwards and deposited its next septum, stopping that new septum from closing completely and becoming mineralised itself.[4]
Ten or more septa are found in mature individuals, occupying around a third of the shell – septa form very early and have been found in specimens as small as 2 mm in length.[5] Unlike monoplacophoran fossils, there is no evidence of muscle scarring in Knightoconus fossils.[5] Scars from the closely related Hypseloconus have been used to determine its orientation.[6] Knightoconus started life with an exogastric shell that became endogastric as the organism grew.[7]
An alternate taxonomy is: Tergomya: Kiringellida: Hypseloconidae.[1]