Haccourtaster Jagt 2000

Genus Haccourtaster Jagt, 2000 Type species. Haccourtaster aemstelensis Jagt, 2000, by original designation. Diagnosis. A small, pentagonal goniasterid in which two superomarginals and two inferomarginals are typically present on each side of the arm. A narrow, depressed margin is present on all marginals, and the raised central region bears coarse granule pits. Blunt internal intramarginal cavities are present between the marginals. Other included species. Haccourtaster hrbac Žítt, 2005, Haccourtaster berryensis sp. nov., Haccourtaster liticola sp. nov. and Haccourtaster nattestadae sp. nov. Remarks. Haccourtaster is a distinctive small goniasterid, which typically occurs in marginal marine Upper Cretaceous facies. Although two inferomarginals are typically present on each side of the arm a small, distal inferomarginal is found on some specimens. The internal intramarginal cavities (Žítt, 2005, fig. 11A) represent short, narrow extensions of the coelom into the marginal frame and are of unknown function. Species are characterised by distinctive marginal morphologies and external sculptures. In the present paper, we describe three new species of the genus. Haccourtaster probably evolved from a species of Metopaster, by retaining four marginals on each side of the disc, either developing paedomorphically from a species with more marginals, or from an ancestor which also possessed four marginals (see below; Discussion). It developed the distinctive intramarginal cavities in the interior of the marginals, and the ultimate inferomarginal became enlarged to correspond with the ultimate superomarginal.