The Echinoid Directory

• Test discoidal with flat base, convex upper surface and moderately thin edge.
• Apical disc slightly posterior with four gonopores.
• Petals long and well developed; weakly bowed and closed or nearly closed distally. Not raised.
• Ambulacral zones larger than interambulacral zones at ambitus.
• Basicoronal circlet pentagonal with interambulacral plates projecting.
• Food groove a primary trunk that trifurcates towards outer edge of first post-basicoronal ambulacral plate; finer branching distally.
• Posterior interambulacrum disjunct, separated by first pair of post-basicoronal ambulacral plates. Other interambulacra continuous.
• Periproct supramarginal, opening in the third or fourth pair of post-basicoronal interambulacral plates.
• Internal partitioning as in Echinarachnius.

Miocene to Pleistocene, Eastern USA seaboard from Alaska to California.

Scutellaster cretaceus Cragin, 1895 [= Scutella interlineata Stimpson, 1856] by original designation.

• S. interlineata (Stimpson, 1856); Pliocene, West coast of USA.
• S. oregonensis (Clark, 1909); Late Miocene, Alaska; Pliocene, Oregon.
• Some or all of the species listed under Kewia and Tenuirachnius.

Clypeasteroida; Scutellina; Scutelliformes; Echinarachniidae.

Presumed monophyletic.

Durham (1953) showed that the genus Scutellaster was identical to Anorthoscutum and placed it in the Dendrasteridae. However, the food groove structure shows Scutellaster to be an echinarachniid and not a dendrasterid, as suggested by Wagner (1974, p. 119). The aboral periproct and the trifurcation of the food groove on the first post-basicoronal ambulacral plate rather than the second, distinguishes Scutellaster from Echinarachnius.

Durham (1955) established the genera Kewia and Tenuirachnius for relatively small individuals with supramarginal periprocts. Oral plating in all is very similar and the periproct is also associated with the third post-basicoronal interambulacral plates. Simple food grooves and simpler internal buttressing distinguish these genera, but this is associated with their small size and do not afford useful diagnostic characters. Furthermore, their basic morphology is common to many juvenile Scutellidea. Nisiyama (1968) showed that juvenile Scaphechinus mirabilis were indistinguishable. However, Kewia does develop gonopores at an earlier growth stage than Echinarachnius parma or Scaphechinus mirabilis. Kewia, Tenuirachnius, Sinaechinocyamus and Taiwanaster all therefore represent small scutellines that have developed sexual maturity at a small size, and could represent offshoots from Scutellaster, Scaphechinus or Echinarachnius. Purely for practical reasons, they are placed here in synonymy with Scutellaster, since all have supramarginal periprocts.

Cragin, F. W. 1895. A new Cretaceous genus of Clypeasteridae. American Geologist 15, 90-91.

J. W. Durham 1953. Scutellaster and Anorthoscutum. Journal of Paleontology 27, 147-149.

C. D. Wagner, 1974. Fossil and Recent sand dollar echinoids of Alaska. Journal of Paleontology 48, 105-123.

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.