The Echinoid Directory

• Small, flattened test up to 7 mm in length. Ovate in outline and tapering posteriorly with widest point of test distinctly posterior of centre. Oral surface flat.
• Apical disc anterior of centre with four gonopores. Hydropores scattered over surface of disc.
• Petals small but distinct; pore-zones parallel and open distally. Plating simple.
• Ambulacral zones a little wider than interambulacral zones at ambitus.
• Interambulacral zones extending as biseries to apical disc.
• Peristome central, relatively large and circular.
• Food grooves simple - at most a shallow perradial furrow close to the peristome.
• Periproct opening on aboral surface near posterior margin; at contact between the first and second pair of post-basicoronal plates.
• Basicoronal plate arrangement not described. Posterior three interambulacral zones disjunct, anterior interambulacral zones continuous.
• Tubercles on oral surface dense and uniform.
• Ten internal partitions only arranged radially.

Recent, Yellow Sea.

Sinaechinocyamus planus Liao, 1979, by original designation.

• Only the type species.

Clypeasteroida; Scutellina; Scutelliformes; ?Echinarachnidae.

Monotypic. Subjective junior synonym of Kewia Nisiyama, 1935.

The biserial interambulacral series of plates adapically distinguish this from all living Laganina. This taxon is apparently identical to Taiwanaster Wang, who gives a much fuller description. The detailed placement of this taxon is problematic because simple internal supports and simple food grooves are common to all juvenile scutellines. The taxon has a striking resemblance to the Miocene Kewia Nisiyama, 1935, but this too is probably based on small individuals of Scutellaster, Echinarachnius or Scaphechinus (see Nisiyama for illustrations of comparable juvenile Scaphechinus mirabilis) Mooi (1990) showed clearly that this was a minaturized scutelline and not a fibulariid.

Liao, Y. 1979 A new genus of clypeasteroid sea urchin from Huang Hai. Oceanologia et Limnologia Sinica 10, 70-74, pl. 1.

Mooi, R. 1990. Progenetic minaturization in the sand dollar Sinaechinocyamus: implications for clypeasteroid phylogeny. PP. 137-143 in C. de Ridder et al. (eds) Echinoderm Research: Proceedings of the Second European Conference on Echinoderms Rotterdam: A. A. Balkema.