knightoconusとは 意味・読み方・使い方

Knightoconus antarcticus is a Cambrian monoplacophoran thought to represent an ancestor to the cephalopods. It had a chambered, conical shell, but lacked a siphuncle. The absence of this siphuncle has been taken as evidence against cephalopod ancestry - how, it is argued, could a siphuncle evolve to penetrate existing septa? 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, producing an obstacle to the complete closure of the septum and becoming mineralised itself. 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. Unlike monoplacophoran fossils, there is no evidence of muscle scarring in Knightoconus fossils. Scars from the closely related Hypseloconus have been used to determine its orientation. Kinghtoconus starts life with an exogastric shell, that becomes endogastric as the organism grows.