Hippasteria Gray 1840

Mah, Christopher L., 2023, New Goniasteridae and in situ observations significant to deep-sea coral predation, Memoirs of Museum Victoria 83, pp. 1-35 : 28

Hippasteria Gray 1840

Diagnosis. Body weakly pentagonal to stellate (R/r=1.5–2.3). Disk and arms thick. Arms relatively broad and short. Tissue with pulpy texture covers abactinal plates. Shallow fasciolar grooves present. Secondary plates present. Abactinal plates, tightly articulated, polygonal to irregular in outline, flat and elevated over surface. Carinal series are poorly distinguished. Abactinal spinelets (sometimes granular) forming fringe around abactinal plates. Spines, large, conical; granules common on abactinal plates. Large spines present on superomarginal and inferomarginal plates of most species. Superomarginal and inferomarginal plates bare, quadrate to rounded in outline at interradii with no other accessories other than large spines. Spinelets present on marginal plates. Shallow fasciolar grooves present between marginal plates. Marginal accessories (granules, spinelets, etc.) differentiated into a fringe on superomarginal and inferomarginal plates. Superomarginal plates dorsal facing in most species, Actinal fasciolar grooves shallow. Large actinal spines and spinelets present. Subambulacral spines large (and thus few in number). Furrow spines large, blunt, and round, usually few. Enlarged bivalved pedicellariae on raised bases on body surface. Modified from Mah et al. (2010, 2014).

Comments. Hippasteria includes 12 species, including the widespread H. phrygiana , which was determined to be a wide-ranging species present in the Pacific, Atlantic and Indian Oceans ( Foltz et al., 2013; Mah et al., 2014). Hippasteria is most immediately distinguished from Evoplosoma based on the presence of large (bisecting the plate on which it sits) bivalve pedicellariae and more broadly shaped disk and arms, and relatively few furrow spines (fewer than four), which are blunt and round in cross-section.

Morphology varies widely within H. phrygiana , with some populations showing more morphological resemblance (e.g. Atlantic and Pacific H. phyrgiana ) than others (e.g. the Japanese Hippasteria imperialis ). Distinction and characterisation of these populations remains ongoing, because it is unclear how or if they should be formally recognised below a species level, especially as new occurrences of H. phrygiana are discovered.

In addition to H. phrygiana, Mah et al. (2014) recognised at least two other species lineages of Hippasteria , H. californica and H. heathi , with closely related and wide-ranging members. Hippasteria muscipula was also described therein (Mah et al., 2014) and is a wide-ranging species throughout the tropical Pacific ( Mah, 2023, unpublished data).