ABSTRACT
Adults of Sinaechinocyamus planus Liao, 1979, a sand dollar from the Yellow Sea, do not exceed 8 mm in length. Taiwanaster Wang, 1984 from the Taiwan Strait and Pliocene deposits on Taiwan, is shown to be a junior synonym of Sinaechinocyamus Liao, 1979. Because he thought that Taiwanaster was intermediate in morphology between the two clypeasteroid suborders Laganina and Scutellina, Wang (1984) gave Taiwanaster special recognition in his reclassification of the Clypeasteroida, and placed Taiwanaster close to the Fibulariidae, in the Laganina (sensu Durham, 1966). However, autapomorphies for the clypeasteroid suborders clearly indicate that Sinaechinocyamus is a member of the suborder Scutellina, not the Laganina. Phylogenetic analysis shows that Sinaech-inocyamus is the sistergroup of the large-tested, northwestern Pacific genus Scaphechinus. Sinaechinocyamus is a highly derived, extremely miniaturized progenetic sand dollar that closely resembles juveniles of Scaphechinus. This vitiates Wang’s supposition that Sinaechinocyamus is a primitive scutelline linking the Laganina and Scutellina.
