Alloceramaster, Mah, 2025

Alloceramaster View in CoL nov. gen.

Etymology. The genus name is based on the Greek “allos” for “other”, alluding to the difference from the established genus Ceramaster .

Diagnosis. Overall body forms pentagonal or weakly stellate (R/r = 1.1–1.9) with few known adults greater in size than R = 2.0 to 5.0 cm. Arm tips blunt. Interradial arcs weakly curved to straight.

Fasciolar grooves present around radial papular regions, but shallow to absent around other abactinal plate regions. Two distinct types of abactinal accessories, the more rectangular to rhombic shaped granules forming a periphery around papular radially positioned, abactinal plates versus those forming round to polygonal granules forming periphery around the remainder of the plates.

Marginal plates per interradius (arm tip to arm tip), 10–18, most bald or with large bald region on plate surface. Actinal plates quadrate to polygonal, covered by granules. Furrow spines 2 to 9, blunt, subambulacral spines 3 to 4.

Comments. Alloceramaster nov. gen. is proposed to accommodate C. grenadensis and other related taxa with shared characters as outlined herein, including P. affinis , C. pointsurae , and two new Australian species. Pentagonaster affinis is designated as the type species for the genus.

Although split from Ceramaster , members of Alloceramaster share more in common morphologically with Sphaeriodiscus , displaying distinctly different abactinal plates present around the papular pore region. Peripheral granules (e.g. Fig. 2A–B) on radial regions differ from interradial regions and elsewhere, separate from other abactinal plates and have more weakly-developed fasciolar grooves. In conjunction with the well-developed fasciolar grooves, typological Ceramaster have well-developed abactinal tabulate plates (e.g. Fig. 10A–C) whereas those in Alloceramaster are shorter and are more weakly developed. Granules in Alloceramaster are smaller, rounder, and more abundant than those observed in typological Ceramaster , which tend to be larger and polygonal in shape. This is in stark disagreement with Clark and Downey’s (1992) taxonomy which argued C. patagonicus as a subspecies of C. grenadensis . Alloceramaster also shares several characters with Bathyceramaster , showing abutted abactinal plates with papular, or proximal fasciolar grooves and demonstrating an abundance of granules present over abactinal and marginal plate surfaces. Alloceramaster and Bathyceramaster tend to occur below 1000 m depths, whereas Ceramaster shows a broad range between 20 and 1500 m.

As with other deep-sea Goniasteridae , such as Bathyceramaster , Alloceramaster is widely occurring in deep-sea settings. Although variation based on morphological data suggests multiple species, independent phylogenetic data for other widely occurring asteroid genera, such as Hippasteria ( Foltz et al., 2013) have suggested some species do not always show morphological, taxonomic and molecular congruence.