6533b82dfe1ef96bd129116f

RESEARCH PRODUCT

A critical comment on ‘ankyroids’ (Echinodermata, Stylophora)

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Abstract A recent cladistic analysis of stylophoran echinoderms performed by Parsley suggested that mitrates are polyphyletic and derived from symmetrical cornutes. Parsley erected the order Ankyroida to include all derived cornutes and mitrates. The present paper addresses several significant problems in the data matrix of Parsley's cladistic analysis. Detailed morphological comparisons of various stylophorans suggest that important homologies have been ignored: cornute zygal crest and mitrate septum, adorals, glossal and digital. Subanals are not homologous in mitrates. Identification of plate homologies shows that similar-looking symmetrical thecal outlines have been acquired independently in various cornute lineages, and that primitive mitrates are fundamentally asymmetrical. A new cladistic analysis using a corrected version of Parsley's original data matrix strongly supports the monophyly of the orders Cornuta and Mitrata. The order Ankyroida is polyphyletic and should be abandoned. The genus Sagittacystis is synonymised with Balanocystites . The anomalocystitid mitrates Australocystis, Allanicytidium, Notocarpos and Tasmanicytidium are synonymised with Placocystella. Drepanocarpos is re-interpreted as a primitive cornute belonging to the stem-group of the Hanusiidae. The cornute Juliaecarpus milnerorum is assigned to the genus Nanocarpus .