The Echinoid Directory

• Test circular to weakly pentagonal. Base flat and upper surface weakly domed.
• Adapical portion of test depressed so that outer margin appears inflated; the depression continues interradially to the ambitus as a narrow channel.
• Apical disc central; 4 gonopores.
• Internal radial partitions well developed and irregular.
• Posterior petals shorter than anterior petals. Petals distally open or converging.
• Interambulacral zones about as wide as ambulacra at ambitus.
• All interambulacrum disjunct on oral surface. The second pair of ambulacral plates greatly enlarged compared to others.
• Periproct marginal; opening between fourth paired interambulacral plates.
• Food grooves present, bifurcating on second paired ambulacrals but without distal branching.

Upper Miocene to Recent of Japan and Formosa.

Scaphechinus mirabilis A. Agassiz, 1863, p. 359, by original designation.

• S. mirabilis A. Agassiz, 1863; Pliocene - Recent, Japan.
• S. tsudai (Morishita, 1950); Miocene, Japan.
• S. griseus (Mortesen, 1927); Pleistocene to Recent, Japan.
• S. raritalis (Nisiyama, 1951); Late Miocene-Pliocene, Japan.

Clypeasteroida; Scutellina; Scutelliformes; Scutellidea;   Scutellidae.

Presumed monophyletic.

The fossil S. tsudai (Morishita) illustrated here differs from the type species S. mirabilis Agassiz only in having more distally open petals. Very close to Remondella in having a marginal periproct, symmetrical petals and central apical disc and bifurcating food grooves, but differing from that genus in having a depressed central zone. It is more clearly different from Dendraster in having symmetrical petals and a marginal periproct.

Mortensen (1948) was not convinced that Scaphechinus could justifiably be separated from some species of Scutella (here treated as Parascutella), but Durham (1955) was able to show that in Scaphechinus the interambulacral zones are disjunct on the oral surface whereas in Parascutella they are just continuous. In other respects the two taxa are very similar.

The growth series of S. mirabilis was described by Nisiyama (1968). Small individuals have a supramarginal periproct and look remarkably like Kewia or Sinaechinocyamus

Agassiz, A. 1863. Synopsis of the echinoids collected by Dr W. Stimpson on the North Pacific Exploration Expedition under the commandant of Captains Ringold and Rodgers. Proceedings of the Academy of Natural Sciences, Philadelphia 15, 352-361.

J. W. Durham 1955. Classification of clypeasteroid echinoids. University of California Publications in Geological Sciences 31(4), 73-198.

Nisiyama, S. 1968. The echinoid fauna from Japan and adjacent regions. Part II. Palaeontological Society of Japan Special Papers 13, 1-491, pls 19-30.

Shigei, M. 1986. The echinoids of Sagami Bay Maruzen Co, Tokyo.