The Echinoid Directory

Echinarachnius Gray, 1825, p. 428

[=Phelsumia Pomel, 1883, p. 70 (non Gray, 1840); =Phelsumaster Lambert & Thiery, 1914, p. 316 (objective) ]

Diagnostic Features
  • Test discoidal with flat base and low conical profile.
  • Internal supports well developed; comprising radial struts along adradii and concentric partitions in ambularal interspaces.
  • Apical disc central; 4 gonopores.
  • Petals well developed; open distally though slightly convergent. Petals never raised.
  • A very slight posterior notch marking the position of the periproct.
  • Anterior and lateral interambulacra continuous adorally, the posterior interambulacrum usually slightly disjunct; separated by first pair of post basicoronal ambulacral plates.
  • Basicoronal circlet strongly pentastellate, with interambulacral plates projecting.
  • Periproct marginal; opening bounded by third pair of interambulacral plates.
  • Food grooves forming long primary trunk that does not divide until the outer edge of the third pair of ambulacral plates and gives rise to two secondary grooves.
  • Ambulacra wider than interambulacra at ambitus.
Miocene to Recent, North Pacific.
Name gender masculine
Scutella parma Lamarck, 1816, p. 11, by subsequent designation of L. Agassiz, 1841, p. 88.
Species Included
  • E. parma (Lamarck, 1816);Pliocene-Recent, Pacific coast from Puget sound North to Alaska and Atlantic coast from Massachusetts North.
  • E. alaskense Durham 1957; Pliocene, Alaska.
  • E. astrodaspoides Wagner, 1974; Middle or Upper Miocene, Alaska.
  • E. humilis Nisiyama, 1968; Pliocene, Japan.
  • E. ishioi Morishita, 1950; Pliocene, Japan.
  • E. laganolithinus Nisiyama, 1940; Pliocene, Japan.
  • E. microthyroides Nisiyama, 1940; Miocene, Japan.
  • E. naganoensis Morishita, 1953; Pliocene/Upper Miocene, Japan.
  • E. plafkeri Wagner, 1974, Upper Miocene, Alaska.
  • E. subtumidus Nisiyama & Hashimoto, 1950; Miocene, Japan.
  • E. ungaensis Wagner, 1974; Middle or Upper Miocene, Alaska.
  • E. brewerianus (Remond); Middle Miocene, California.
Classification and/or Status

Clypeasteroida; Scutellina; Scutelliformes; Echinarachniidae.

Presumed monophyletic.


Echinarachnius can be distinguished from the type species of Astrodaspis by its periproct positioned in the second or third post-basicoronal interambulacral plates, and by its less disjunct interambulacra (the anterior interambulacra are never widely disjunct). Faassia Schmidt is closely similar, but oral plating remains undescribed and the periproct is distinctly oral in position. Pseudastrodapsis is distinguished by its very much narrower interambulacral zones. Scutellaster differs in having the periproct supramarginal, associated with the third and fourth post-basicoronal plates, and food grooves trifurcating at the end of the first rather than second post-basicoronal ambulacral plates.

Agassiz, L. 1841. Observations sur les progress récens de l’histoire naturelle des echinoderms. Monographie d’Échinodermes vivans et fossiles. Seconde Monographie, première section, 20 pp. Petitpierre, Neuchâtel.

Mortensen, T. 1948. A Monograph of the Echinoidea IV.2 Clypeasteroida. C. A. Reitzel, Copenhagen.

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 Paper 13, 1-491, pls 19-30.