The Echinoid Directory

• Test ovate with prominent anterior sulcus; slightly pointed to rear.
• Apical disc ethmolytic, with 4 gonopores (the anterior pair usually smaller than the posterior pair).
• Anterior ambulacrum deeply sunken aborally, but forming only a modest notch at the ambitus; pore-pairs and tube-feet specialized; uniserially arranged.
• Other ambulacra petaloid and obviously sunken, anterior petals about twice as long as the posterior petals; petals cruciform and not particularly strongly flexed.
• Single pair of elongate, triangular plates in the three posterior interambulacra between the peripetalous fasciole and apex in type species.
• Periproct near top of vertical truncate face.
• Peristome large and kidney-shaped; labral plate not strongly projecting, so peristome downward-facing.
• Labral plate short and wide; not extending beyond first ambulacral plate; in broad contact with sternal plates. Sternal plates large and symmetrical. Episternal plates offset and forming lowest part of posterior.
• Aboral tuberculation fine, uniform and dense. Oral tubercles also dense and uniform.
• Well-developed peripetalous and latero-anal fascioles.
• Subanal penicillate tube-feet well developed.

Eocene to Recent, low and mid latitudes.

Shallow water silts and muds - infaunal.

Schizaster gibberulus L. Agassiz, 1847, p. 128, by original designation.

• P. exoletus Hutton (1873); Upper Eocene to Upper Oligocene, New Zealand.
• P. rotundatus (Doderlein, 1917); Recent, Galapagos Islands.
• P. gibberulus (Agassiz, 1847); Recent, Red Sea and Indian Ocean.
• P. compactus Koehler, 1914; Recent, Indian Ocean.
• P. santamariai Gauthier, in Fourtau, 1900; Lower Eocene, Egypt.
• P. zitteli de Loriol, 1880; Lower Eocene, Egypt.
• P. delorenzoi Checchia-Rispoli, 1950; Middle Eocene, Somalia, Qatar.
• P. ambulacrum Deshayes, 1831; Lower Oligocene (Stampian), France.
• P. ashrafi Ali, 1985; Lower Pliocene. Red Sea.
• P. nummuliticus (Tokunaga, 1903); Middle Eocene (Lutetian), Bonin Island.
• P. saipanicus Cooke, 1957; Miocene, Micronesia.

Spatangoida, Paleopneustina, Schizasteridae.

Subjective junior synonym of Schizaster Agassiz, 1836.

Mortensen (1951) distinguished Paraster from Schizaster on the number of genital pores in the apical disc (Paraster having four gonopores and Schizaster supposedly two). Unfortunately the type species of Schizaster, S. studeri Agassiz, turns out to have four gonopores, of which the anterior pair are reduced compared to the posterior pair. Schizaster and Paraster must therefore be considered synonyms.

Differs from Diploporaster in having four gonopores and aboral pore-pairs in ambulacrum III arranged uniserially, rather than forming a double column. Periaster is similar in appearance but has an ethmophract apical disc.

Pomel, A. A. 1869. Revue des échinoderms et de leur classification pour servir d’introduction à l’étude des fossiles, 67 pp. Deyrolle, Paris.