Alloceramaster leios, Mah, 2025

Alloceramaster leios View in CoL nov. gen, nov. sp.

Figures 4A–E

Material Examined. Holotype. MV F240274 . Great Australian Bight. 34º 46' 30" S, 131º 43' 53" E to 34º 47' 56" S, 131º 44' 41" E, 1323– 1340m, Coll. IN 2015_COI GAB Chevron. 22 November 2015. 1 wet spec. R = 2.4 r = 1.5. GoogleMaps

Paratypes. WAM Z 110247. 147 km WNW of Koks Island, outside the Gascoyne Marine Park , 23º 59' 20.112" S, 111º 58 ‘8.4612" E, 1025 m 8 wet specs. Coll. B. Alvarez, K. M. Naughton, K. Moore, C. Unteidt, aboard GoogleMaps RV Investigator CSIRO 10064562, 8 wet specs. R = 1.2 r = 0.7, R = 1.2 r = 0.7 R = 1.2 r = 0.7, R = 1.2 r = 0.7 R = 1.1 r = 0.6, R = 1.1 r = 0.6 R = 0.9 r = 0.5, R = 0.6 r = 0.4

Etymology. The species epithet is derived from the Greek leios for smooth or bald, alluding to the smooth, bare superomarginal plate surfaces.

Diagnosis. Body weakly stellate (R/r = 1.6), interradial arcs curved. Arms triangular. Abactinal plates weakly tabulate along papular regions, plates rounded to polygonal in shape.

Granules more uniform, densely arranged with less distinction between those centrally and peripherally. Radial regions with fasciolar grooves, plates hexagonal to round, peripheral granules trapezoidal with central granules round to polygonal. Marginal plates 14 to 16 per interradius (arm tip to arm tip), penultimate superomarginal enlarged, abutted distally. Superomarginals with prominent bald area occupying central region. Furrow spines, blunt, round in cross-section, 4 to 6, mostly 4 or 5 with six spines present closer to arm tip in weakly palmate arrangement. First row of subambulacral spines, primarily three but some with four, set apart from furrow spines by distinct space.

Comments. Alloceramaster leios n. sp. shares distinctive characters with A. minus sp. suggesting affinities, notably that the superomarginal plate surface is bare and smooth, either completely or as a distinct patch on the dorsal surface. The papular regions, also show plates with peripheral granules that are similar in appearance ( Fig. 4B). Alloceramaster leios shows an enlarged, penultimate superomarginal plate distinguishing it from other known Alloceramaster species. Although the enlarged penultimate superomarginal invokes comparisons with Sphaeriodiscus , Alloceramaster displays heterogeneous peripheral granules between the radial and interradial areas and has superomarginal plates with smooth, bare dorsal areas with no granules present. Marginal plate number in Alloceramaster , 10 to 18, which is generally more stellate is also greater than in Sphaeriodiscus , 6 to 12, which is generally more pentagonal.

The small sized individuals suggest greater development of marginal plate number and granule number relative to that observed in the holotype (at R = 2.4) as well as a more stellate shape in larger individuals. If assessment of WAM Z110247 About WAM as small individuals is correct, the distribution of this species extends from the South Pacific to the Indian Ocean, suggesting widespread occurrence .

Occurrence/Distribution. Great Australian Bight, 1323–1340 m. Gascoyne Marine Reserve (1025m).

Description. Body weakly stellate (R/r = 1.6 to 1.7), interradial arcs curved. Arms triangular ( Fig. 4A).

Abactinal plates weakly tabulate, extending from disk to arm tip. Fasciolar channels present primarily over radial papular regions ( Fig. 4A, B), weakly present or shallow interradially. Abactinal plates polygonal to round in outline with weakly convex surface. Plates covered by 10 to 70 granules. Peripheral granules show distinct shape difference between those present radially and interradially. Those present along radial regions with peripheral granules, 10 to 30 distinctly trapezoidal in shape ( Fig. 5B). Other granules, 8 to 30, present on central and interradial regions round in outline. Radial granules widely spaced. Granules interradially and within the primary circlet with more weakly differentiated peripheral and central granules. Peripheral and central granules more closely homogeneous in size and shape, and more densely arranged. Peripheral and central granules also more homogeneous, closer in shape and size relative to those on the radial regions. Radial plates include eight to nine granules across a 1.0 mm line. Superomarginal plates abutted distally, forming distinct border, approximately 10% of total distance “r” ( Fig. 4A). Madreporite quadrate in shape, concave curvature, flanked by four plates. A distinct dividing contact present along each interradius between plates present on the disk. Pedicellariae not observed.

Superomarginal plates 14, inferomarginals 16 per interradius, arm tip to arm tip. Eight at R <1.2. Penultimate superomarginal plates enlarged, oblong approximately twice the size of the adjacent superomarginal plate and completely devoid of granules. Superomarginal with prominent, round bald area occupying most of abactinal facing surface ( Fig. 4C). Dense, round granules, counting approximately 50 to 70 on lateral facing of superomarginal plate ( Fig. 4C). Superomarginals and inferomarginals with peripheral granules, round in shape, approximately 40 to 80. Interradially with 15 on each short side, 20 on each elongate side. Pits corresponding to tong-like pedicellariae present on bare plate surface. Superomarginal contact with abactinal plates convex. Inferomarginal oral surface with round bald spot variable in size from three to four granules wide to completely covering inferomarginal surface, otherwise covered by 20 to 100 round granules, continuous with granules on actinal surface. Terminal plates triangular, smooth surface.

Actinal surface with three full rows in chevron-like pattern with one to two irregular, incomplete rows. Plates quadrate in shape, each covered by eight to 30 round to polygonal evenly shaped granules ( Fig. 4D, E).

Furrow spines, blunt, teardrop in cross-section, 4 to 6, ( Fig. 4E) mostly 4 or 5 with six spines present closer to arm tip in weakly palmate arrangement. First row of subambulacral spines, primarily three, but some with four set apart from furrow spines by distinct space. This row 50–60% of furrow spine height, with each spine about twice as thick as each furrow spine. Two further rows of subambulacral granules or short spinelets present on adambulacral plate, gradually decreasing in size until becoming consistent in size with other actinal granules. Each subambulacral row with spaces between them. Oral plate furrow spines 12, blunt, more quadrate in cross-section with one distinct spine, blunt-tipped, quadrate in cross-section, from each plate directed into mouth. Oral plate surface with two paired series of six angular granules along oral plate centre contact. Approximately seven to nine other angular or quadrate in cross-section spines present on oral plate surface.

WAM Z110247 About WAM shows eight specimens with overall R <1.2 cm. These show much more weakly developed abactinal plates, and shallower fasciolar grooves around the papular regions. Coarse, angular granules, 3 to 10 per plate, with fewer on papular regions. Marginal plates 8 per interradius, superomarginal dorsal face completely bald, inferomarginal plates surface covered by quadrate shaped bald spot, surrounded by granules. Furrow spines 2 to 4, mostly 3. Subambulacral spines decreasing in size, shape from furrow to actinal intermediate surface.