New Carboniferous Ophiuroid From Central Coastal New South Wales

The ophiuroid Bronthaster retus gen. et sp. nov. is described from a single specimen preserved as external dorsal and ventral moulds, and is assigned to the Protasteridae. It occurs in the Namurian (Levipustula levis Zone) Yagon Siltstone of the Myall Lakes district of central coastal New South Wales. This rock unit forms part of the structurally designated Myall Block at the southeastern coastal termination of the Tamworth Belt. This new genus is the first stelleroid to be described from the Carboniferous in Australia. Most distinctive of the new genus is the arrangement of many small, subrhomboidal to subpentagonal, overlapping ossicles on the dorsal surface of the arms. The clearly exhibited tight relationship between successive ambulacrals in one column in ventral view suggests that some revision of previously inferred relationships within ambulacral columns in protasterids is required. The position of prominent toehooks on each ambulacral ossicle shows that they functioned to prevent lateral movement of the ambulacral column, operating in conjunction with the strong longitudinal musculature to allow arm flexure in the horizontal plane. This feature could potentially identify, within the Protasteridae, an evolutionary lineage that proceeded through the middle Palaeozoic and maintained the linear arrangement of the ambulacral columns using the toehooks, rather than fusion of the ambulacral ossicles across the arm axis.