Sphaeriodiscus Fisher, 1910

Mah, Christopher L., 2018, New genera, species and occurrence records of Goniasteridae (Asteroidea; Echinodermata) from the Indian Ocean, Zootaxa 4539 (1), pp. 1-116 : 82

Sphaeriodiscus Fisher, 1910

Sphaeriodiscus Fisher, 1910: 171 ; 1911: 167; Tortonese & A.M. Clark, 1956: 343; Halpern, 1970b: 79; A.M. Clark & Courtman-Stock, 1976: 249; Downey in Clark & Downey, 1992: 265; H.E.S. Clark & McKnight, 2001: 133; Mah 2011: 44.

Diagnosis. Body pentagonal (e.g., Fig. 31A ). Abactinal plates weakly tabulate, covered by evenly distributed granules (e.g. Fig. 31B ). Marginal plates few, tumid with swollen or enlarged penultimates (e.g., Fig. 31C ). Pedicellariae spatulate.

Comments. Sphaeriodiscus together with Peltaster and Ceramaster , which all share similar defining characters, including a pentagonal body shape, relatively few marginal plates, shallow to well-developed abactinal plates, granule-covered, either partially or completely, marginal plates with bald region on the superomarginal surface, and variably granule to spinelet covered abactinal and actinal surfaces. Several characters present among species within these genera overlap or else show poor correspondence with taxonomic concept boundaries.

Seven species of Sphaeriodiscus are currently recognized (Mah, 2018), including five Pacific species, one Atlantic species, Sphaeriodiscus bourgeti , and Sphaeriodiscus mirabilis from the southern Indian Ocean, included herein. Fisher (1906) established Sphaeriodiscus based on an enlarged “ultimate or ante-penultimate” superomarginal plate. Not all of these species fall within the constraints of the original genus definition as clearly as the type species, Sphaeriodiscus ammophilus . Enlarged near-terminal superomarginals are present in many species of each genus and in some specimens, enlarged plates are variably, absent or weakly developed. There has, for example, been some question as to the placement of Peltaster placenta in Peltaster or Sphaeriodiscus (e.g. Tortonese and Clark 1956, Tortonese 1984). Subsequent authors, such as H.E.S. Clark and McKnight (2001), have liberally applied the enlarged ultimate/antepenultimate marginal plate criterion and differing definitions of “enlarged” have qualified different species as Sphaeriodiscus versus Peltaster.

Type Specimen Note. Perrier’s original type series of Sphaeriodiscus bourgeti is in the MNHN collections, rendering Halpern’s (1970) conclusion that the MCZ specimens were the only extant types incorrect and designation of the specimens as lectotype and paralectoype inappropriate.

Figures

FIGURE 31. Sphaeriodiscus biomaglo n. sp. Holotype IE-2013-17197. R=3.3, r=2.2 cm. A. Abactinal surface. Scale bar=1.0 cm. B. Closeup showing abactinal plates and granulation. Scale bar=0.5 cm. C. Arm tip and superomarginal plate surface. Scale bar=0.5 cm. D. Actinal plate surface. Scale bar=1.0 cm. E. Closeup of furrow and adambulacral spination. Scale bar=0.3 cm.