Tetramery in a cidarid sea urchin (Echinodermata: Echinoidea: Cidaridae): documentation of a rare developmental condition

Tetramery is a rarely documented developmental condition in cidarid sea urchins, which are otherwise characteristically pentamerous. Here, a tetramerous specimen of Goniocidaris tubaria (Lamarck, 1816) from Western Port Bay (Victoria, Australia) is described and illustrated using high-resolution photography. This contribution provides a permanent morphological record of an uncommon echinoid developmental anomaly.