Pergamaster ultra Mah 2018, n. sp.

Pergamaster ultra n. sp.

Figure 28 A–E

Etymology. The species epithet ultra is Latin for “beyond” or “on the other side”, alluding to Pergamaster ’s first occurrence from beyond the Antarctic region.

Diagnosis. A species distinguished by its weakly stellate shape (R/r=1.76) (Fig. 28A), bare, smooth abactinal plates (Figs. 28A, B), surrounded by large peripheral granules. Marginal plates, bare smooth, form distinctive frame as viewed from above (Figs. 28A, B). Granule covered actinal surface. Furrow spines three or four (Fig. 28D).

Comments. The bare abactinal plates and distinctively large peripheral granules around plates as well as the wide, smooth bare marginal plates serve to identify this specimen as a member of the genus Pergamaster, a genus known previously only from the Antarctic (Mah 2011).

Mah (2011) outlined two accepted species, Pergamaster incertus from the Weddell Quadrant and Pergamaster triseriatus from the Ross Sea. Both Antarctic species share several characters absent from Pergamaster ultra n. sp, including a thick, enlarged subambulacral spine, and relatively few (two or three) thickened furrow spines (Fig. 28D), as well as much more elongate, triangular arms. This species shows overall, much finer actinal and adambulacral granulation and accessories, including more slender subambulacral and furrow spination. The holotype is also much smaller (R=2.3) than the known Antarctic species, which displayed arm radii of at least 6.0 cm.

Biogeographic Significance. Pergamaster ultra n. sp. represents the first species of this genus to be found outside of the Antarctic region. Several asteroid genera and species are known to occur in both the Antarctic and in “outside” deep-sea settings. The genus Odontaster (Odontasteridae) for example, as outlined in A.M. Clark (1962), Clark & Downey (1992), Fisher (1910) and Clark and McKnight (2001) are most diverse in the Antarctic region but have species representation in the North Pacific, the tropical Atlantic, and the South Pacific region near New Zealand, primarily from deep-water settings. Full phylogenetic work on relationships within such a group remains incomplete and it is unclear whether these species are immigrants from the Antarctic region or are perhaps colonists from external habitats which have exploited Antarctic settings.

Occurrence. Glorioso Islands, off Mozambique, 753–824 m

Description. Body weakly stellate (R/r=1.76), arms triangular, interradial arcs curved. Disk markedly convex (Fig. 28A, C).

Abactinal surface flat, plates level with superomarginal surface. Individual plates round to polygonal (Fig. 28A) with a weak but discrete carinal series composed of plates approximately 10% smaller than those present adradially and interadially. Plates present only on disk, none extending onto arms. Abactinal plate surfaces completely smooth and bare with no surficial accessories. Individual plates with rounded, quadrate to polygonal granules, 15–40, mostly 20–30, evenly spaced around edge, flush with abactinal surface. Granules approximately 1/4 of distance of plate diameter plus peripheral granules. Madreporite irregular in shape, nearly flat, sulci strongly developed, flanked by four plates and their peripheral granules. Papular pores weakly present around radial regions, but no papulae clearly observed. No pedicellariae observed.

Superomarginals, 14, inferomarginals, 16 in each interradius (arm tip to arm tip) forming slightly offset series from one another, resulting in weakly zigzag contact between them. Distalmost four superomarginal plates abutted (Fig. 28B), forming zigzag contact along midline between theme. Superomarginals quadrate, but elongate in outline becoming shorter and more quadrate distally adjacent to terminal plate. Surface of superomarginal plates smooth and bare, devoid of surficial accessories. Peripheral granules round, deciduous, approximately 40 to 80, resulting in approximately 20 granules per side. Inferomarginal plates elongate becoming quadrate distally, surface smooth and bare on actinal surface but lateral surface with 20–40 round, deciduous granules identical in size and morphology with those forming periphery around marginal plates. Bare region larger extending completely over inferomarginal surface to arm tip. Actinal surface of inferomarginals with second row of granules on plate surface adjacent to peripheral series adjacent to actinal plate contact. Terminal plate triangular with bare surface.

Actinal surface composed of three distinct series in chevron formation with shallow fasicolar grooves present (Fig. 28C). Plates quadrate in outline becoming more irregular adjacent to contact with inferomarginal plates. Actinal plates covered with six to 36, mostly 20–30 coarse, well-spaced, homogeneous granules forming weakly ordered rows on each plate. Peripheral series not distinguished.

Furrow spines, three proximally numbering four more distally (Fig. 28D). Spines blunt tipped, cylindrical to rounded, quadrate in cross-section. Subambulacral spines, proximally two becoming three, separated by a space, immediately adjacent to furrow spines (Fig. 28D). Largest subambulacral distal relative to shortest subambulacral spine present proximally on adambulacral plate. Subambulacrals approximately twice as thick as furrow spines. Remaining subambulacral granules in two irregular rows composed of approximately two or three rounded blunt granular spines. Oral plates with nine blunt furrow spines and a single blunt, spine per oral plate (two projecting into mouth), cylindrical in cross section. Oral plate surface with six to nine, short, blunt suboral granules per half plate as well as six to eight paired granules paired up around a distinct well-developed sulcus centrally located on the oral plate.

Material Examined. Holotype: MNHN-IE-2013-17279, Glorioso Islands, off Mozambique, 11°22,7’S, 47°17,2’E 753–824 m. Coll. Pamela-MOZ01, DW01.28 Sept. 2014. 1 wet spec. R=2.3 r=1.3