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The Echinoid Directory

Schizaster L. Agassiz, 1836, p. 185

[=Paraster Pomel, 1869, p. 14; type species Schizaster gibberulus L. Agassiz, 1847; =Aplospatangus Lambert, 1907, p. 113, type species Schyzaster eurynotus Sismonda 1842; =Prymnaster Koehler, 1914, p. 187,type species P. angulatus Koehler, 1914, p. 187; =Rotundaster Lambert & Thiery, 1925, p 526, type species Schizaster foveatus Agassiz, 1889, p. 350; =Brachybrissus Pomel, 1883, p. 37, type species Spatangus ambulacrum Deshayes, 1831.


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Diagnostic Features
  • Test ovate with deep anterior sulcus; slightly pointed to rear.
  • Apical disc ethmolytic, with 4 gonopores.
  • Anterior ambulacrum deeply sunken; pore-pairs in adapical portion large and specialized.
  • Other ambulacra also deeply sunken, anterior petals longer and more flexed than posterior petals.
  • Periproct small and marginal, on near-vertical truncate face. Bound by Iamb. plates 5a/b on oral side.
  • Peristome opening facing anterior; kidney-shaped.
  • Labral plate short and wide; not extending beyond half-way along the first amb. plate; in broad contact with sternal plates. Sternal plates large and symmetric; sternal episternal suture at rear of amb plate 5.
  • Aboral tuberculation fine, uniform and dense Oral tubercles also dense and uniform.
  • Well-developed peripetalous and lateral fascioles. Peripetalous fasicole indented by three plates behind anterior petals; crosses amb III at plate 7 or 8. Latero-anal fasciole branches off about one-third up from the ends of the anterior petals on plates 1.b.5 and 4.a.5.
Distribution
Eocene to Recent; worldwide.
Name gender masculine
Type
Schizaster studeri L. Agassiz, 1836, p. 185, by ICZN ruling, 1948.
Species Included
  • S. studeri Agassiz, 1836; Upper Eocene (Priabonian), southern Europe (the type is from Verona, Italy).
  • S. exoletus (Hutton 1873); Upper Eocene to Upper Oligocene, New Zealand.
  • S. rotundatus (Doderlein, 1917); Recent, Galapagos Islands.
  • S. gibberulus (Agassiz, 1847); Recent, Red Sea and Indian Ocean.
  • S. compactus (Koehler, 1914); Recent, Indian Ocean.
  • S. santamariai (Gauthier, in Fourtau, 1900); Lower Eocene, Egypt.
  • S. zitteli (de Loriol, 1880); Lower Eocene, Egypt.
  • S. delorenzoi (Checchia-Rispoli, 1950); Middle Eocene, Somalia, Qatar.
  • S. ambulacrum (Deshayes, 1831); Lower Oligocene (Stampian), France.
  • S. eurynotus Sismonda, 1842; Miocene, circum Mediterranean.
  • S. fosteri McNamara & Philip, 1980; Miocene, Australia
  • S. carinatus McNamara & Philip, 1980; Palaeocene-Eocene, Australia
  • S. tatei McNamara & Philip, 1980; late Eocene, Australia
  • S. abductus Tate, 1891; Miocene, Australia
  • S. halli McNamara & Philip, 1980; Miocene, Tasmania
  • S. sphenoides Hall, 1907; Miocene, Australia
  • plus many more...
Classification and/or Status

Spatangoida, Paleopneustina, Schizasteridae.

?Paraphyletic (by exclusion of Ova).
Remarks

The number of genital pores in the type species, S. studeri, is not preserved in the holotype and was assumed by Mortensen (1951, p. 296) to be two in number based on a statement by Lambert. A well preserved specimen from the type locality, BMNH E2539 (illustrated above) shows four gonopores, with the anterior pair less well developed than the posterior pair. Mortensen (1951) maintained Schizaster and Paraster as discrete genera, on the mistaken belief that the type species of Schizaster had but two gonopores. It is now clear that there are no differences of any substance between Schizaster studeri Agassiz and Paraster gibberulus (Agassiz), so the two are here synonymized. The same apical disc structure is also seen in the type species of Aplospatangus, Schizaster eurynotus, which also falls into synonymy.

Schizasterids with well-developed latero-anal portion of the marginal fasicole and with two gonopores only are here treated as members of the genus Ova.