Redescription of the Australian mitrate Victoriacystis with comments on its functional morphology

Abstract

Re-examination of the type material, and study of new specimens of the Upper Silurian mitrate Victoriacystis wilkinsi Gill & Caster from the Heathcote area of Victoria, Australia, reveal additional details of its anatomy. Mitrates from the Lower Silurian of Hawthorn and the Lower Devonian of Kinglake West (Victoria, Australia) are assigned to V. wilkinsi. New morphological features of Victoriacystis are: a sculptured median upper lip plate; five transverse rows of ventral plates; a complex ornament on the internal surface of the anteriormost ventral plates; a flexible articulation between dorsal and ventral fore-tail plates; and the presence of knobs on the ventral hind-tail plates. Victoriacystis was probably a semi-infaunal animal which moved rearward within the sediment pulled by its tail. Yawing was reduced by the deep lateral head walls. The fore-tail could be flexed laterally to a large extent, whereas the hind-tail could proably also act as a lever. Spines might have helped the animal to rest on sediment, to increase stability in water currents, and/or to bring food particles in suspension.