Three new species of the echinoid genus Monostychia Laube, 1869 from Western Australia

Abstract

Sadler, T., Martin, S.K. & Gallagher, S.J., February 2017. Three new species of the echinoid genus Monostychia Laube, 1869 from Western Australia. Alcheringa 41, 464–473. ISSN 0311-5518Three new species of the extinct echinoid genus Monostychia Laube, 1869 are described from Western Australia. All are from the middle Miocene Colville Sandstone of the Eucla Basin and have historically been referred to this genus without description. These new taxa differ from previously described Monostychia species in several morphological features, such as size and shape but also in the number of post-basicoronal interambulacral plates developed in the oral paired interambulacrum, a feature considered taxonomically important at both genus and species level for clypeasteroids. The number of ambulacral plates in the paired and unpaired oral regions is also considered a potentially diagnostic taxonomic feature for this genus; it is concluded that the oral ambulacral plate count, particularly that of the unpaired ambulacrum III, is at least as useful a taxonomic feature as the oral interambulacral plate count.Tony Sadler [t.sadler@student.unimelb.edu.au] and Stephen J. Gallagher [sjgall@unimelb.edu.au], School of Earth Sciences, University of Melbourne, Victoria 2010, Australia; Sarah K. Martin [sarah.martin@dmp.wa.gov.au], Geological Survey of Western Australia, Department of Mines and Petroleum, Western Australia, 6004.