The Echinoid Directory

Gibbaster Gauthier, 1888, p. 381

[=Isomicraster Lambert, 1901, p. 959; type species Micraster senonensis Lambert 1895, p. 239; = Pseudoepiaster Seunnes, 1888, p. 803 (nomen nudum) ]

Diagnostic Features	Test ovate with distinct anterior sulcus; posterior face truncate. Test subconical in profile. Apical disc ethmophract with four gonopores; central. Ambulacra all similar; all five ambulacra petaloid aborally and weakly sunken. Petals with smooth, undivided perradial zone. Peristome close to anterior border and facing forward into frontal groove. Labrum projecting to cover peristome in oral view. Plastron plating with symmetical sternal plates. Periproct on posterior truncate face; well below mid-height in posterior view. Subanal fasciole present in type species (can be rudimentary or missing); ovate.
Distribution	Upper Cretaceous (Turonian to Campanian), Europe, former Soviet Union, North Africa.
Name gender	masculine
Type	Micraster fastigatus Gauthier, 1887, p. 237 (= Micraster gibbus Desor, 1858, p. 365 non Lamarck, 1816), by subsequent designation of Lambert & Thiery, 1924, p. 483.
Species Included	G. fastigatus (Desor, 1858); Lower Campanian, Western Europe to Kopet Dag. G. brevis (Desor, 1847); Upper Turonian to Lower Campanian, Europe and North Africa. G. sp. (Ernst, 1970); Upper Santonian - Lower Campanian, Germany. G. senonensis (Lambert, 1895); Santonian-Campanian, Europe. G. stolleyi Lambert, 1901; Campanian, North Africa, Europe and Ukraine. ?G. dallonii (Lambert, 1910); Campanian, Poland, Senonian, Pyrenees. G. sp. (Ernst, 1970); Turonian, Germany.
Classification and/or Status	Spatangoida, Micrasterina, Micrasteridae. Presumed monophyletic (with inclusion of Isomicraster species).
Remarks	Differs from Micraster in having all five ambulacra petaloid aborally, and in being more conical in profile, with the periproct positioned below mid-height. Traditionally such forms with a subanal fasciole have been placed in the genus Gibbaster Gauthier, 1888, while forms lacking a subanal fasciole as adults have been placed in the genus Isomicraster Lambert, 1901. According to Ernst (1970) these all form a single lineage within which the subanal fasciole is variably developed. There remain significant taxonomic problems within this genus (see Stokes, 1976). Very close to Pseudogibbaster, which differs in having a less labiate peristome and a higher periproct opening. Note that Gibbaster Seunes 1889 (type species Gauthieria munieri Seunes) refers to a different taxon and is a junior homynym. Seunes genus is now Tholaster. Ernst, G. 1970. Zur Stammesgeschichte und stratigraphischen Bedeutung der Echiniden-Gattung Micraster in der nordwestdeutschen Oberkreide. Mitteilungen aus dem Geologisch-Palaontologischen Institut der Universitat Hamburg 39, 117-135. Gauthier. V. 1888. Bulletin de la Societe des Sciences historiques et naturelles de l'Yonne 41, p. 381. Stokes, R. B. 1976. Distinction between sympatric species of Micraster (Echinoidea) from the English Chalk. Palaeontology 19, 689-697.