Pillsburiaster ernesti ( Ludwig, 1905 )

Mah, Christopher L., 2016, Deep-sea (> 1000 m) Goniasteridae (Valvatida; Asteroidea) from the North Pacific, including an overview of Sibogaster, Bathyceramaster n. gen. and three new species, Zootaxa 4175 (2), pp. 101-141 : 127-129

Pillsburiaster ernesti ( Ludwig, 1905)

Figure 9 A–F

Ludwig, 1905: 136 (as Pentagonaster );

Halpern, 1970c: 3; Maluf 1988:34, 118 (as Pillsburiaster )

Neolectotype designation. As outlined by Ahearn (1995) the type specimen deposited in the NMNH collections was termed a syntype, seemingly due to Ludwig’s designation of two type specimens from Albatross station 3362 with the same catalog number. This second specimen is missing from the collection. As the only extant type material ( Fig. 9 A–C), this specimen is more accurately designated as the neolectotype. There is no indication that that the other syntype is extant but also none that it has been lost, and so its discovery and subsequent designation as the lectotype remains possible.

Comments. This species varied significantly across its range, ranging from a more weakly stellate form with with short arms (neolectotype with R=3.1) to a more strongly stellate form with more elongate arms (specimen SIO E1613). Superomarginal plates are much wider in the southern forms with more northern individuals displaying intermediate superomarginal plate shapes varying from quadrate to more elongate in outline. However, morphological characters of other specimens, including number of furrow spines, abactinal and marginal granulation, and number of superomarginal plates are broadly consistent with those of the holotype given some accommodation for size and variation. Differences are observed at extreme ends of the range but intermediate in form do not support species-level separation.

In situ observations. Individuals of this species were observed on basalt rocks.

Occurrence. Cocos Island , Costa Rica, President Jackson Seamounts B and C. 1416.5–2149 m.

Description. Body weakly stellate to stellate (R/r=1.93–2.5) disk broad, with triangular arms, ranging from short to weakly elongate. Interradial arcs broadly curved to straight ( Figs 9 A–F).

Abactinal surface composed of abactinal plates round to polygonal in outline, forming distinct mounds each covered by large, coarse granules, four to 20 per plate ( Fig. 9 B). Abactinal plates present on disk up to area where superomarginals abut. Patchy regions with granules reduced or absent from plate surface bare but other plates completely covered with granules. Radial regions with granules reduced or absent from plate surface but other plates completely covered with granules. No clear differentiation between central and peripheral granules. Granules crowded, more evenly proximally and in radial regions, becoming more densely arranged interradially and in distal areas adjacent to superomarginals. At R=2.8, three to four granules counted along a 1.0 mm line. At R=3.1, two to three granules counted along a 1.0 mm line. At R=3.6, four granules are counted along a 1.0 mm line. Shallow to absent fasciolar grooves between plates. Large papulae four to six around each plate, present in radial regions, absent interradially. Madreporite pentagonal to round, flanked by five to eight plates. When pedicellariae present, they are small and tong-like but fewer than four per individual were observed.

Marginal plates, 18–28 superomarginals, 20–30 inferomarginals with distinct abactinal facing border. Distalmost three to four superomarginals abutting over midline with fourth superomarginal sometimes with side of plate in contact with paired superomarginal ( Fig. 9 D,E). Superomarginals strongly convex, especially distally. Central surface smooth and bare with periphery composed of coarse granules, 24–30 similar to those on abactinal surface. In North Pacific individuals, granular covering is more reduced and continuous with abactinal granulation, resulting in an essentially bare superomarginal plate surface( Fig. 9 D). Inferomarginals also mostly with bare surface, peripheral granules, 40–60, form distinct boundary around each plate. Granular abundance and extent is variable. In the type ( Costa Rica), granules present on central surface of inferomarginals interradially but becoming bare on distal marginal plates. On the North Pacific specimen granules absent on distalmost marginal plate surfaces ( Fig. 9 E) Each superomarginal wide (W>L) especially interradially at R=3.1 and especially distally adjacent to armtip. Some individuals with more elongate (L>W) to quadrate superomarginals interradially at comparable sizes (R=3.1) ( Fig. 9 E). Smaller individual with more distal superomarginals becoming more quadrate in outline. Superomarginals flat to rounded in cross-section especially distally on arm. Inferomarginals slightly offset from superomarginals forming extended shelf below superomarginal series. Contact with superomarginals interradially with granules obscuring boundary between the two plate series. No pedicellariae on marginal plate surfaces. Terminal plates with smooth surface, triangular in shape.

Actinal surface composed of quadrate to polygonal plates arranged in two to three chevron-shaped series ( Fig. 9 C). Each plate covered with three to 15 coarse, round or quadrate granules, approximately two or three along a 1.0 mm line (at R=3.6), three or four along a 1.0 mm line (at R=2.8). Granules on smaller specimen much more widely spaced apart. One or two paddle-shaped pedicellariae present on about 10% of plates in North Pacific specimen.

Adambulacral plates rectangular ( Fig. 9 C). Furrow spines, blunt tipped, four to six. Neolectotype (at R=3.1) with thickened spines, nearly quadrate in cross-section. USNM 1407954 at R=2.8, spines also blunt and slender. Subambulacral spines two to six (two to three in North Pacific specimens) blunt, thickened (similar to furrow), round to quadrate in cross-section but not in any particular order. A single tong-like pedicellariae present on each adambulacral behind/adjacent to the subambulacral spines. North Pacific individual with pedicellariae absent, but subambulacrals otherwise identical ( Fig. 9 F). Oral plate furrow spines 12–13, blunt tipped, quadrate in cross section ( Fig. 9 C, F). Spinelets, five to seven (mostly six) on each paired half of oral plate. Oral plate surface with three to five spinelets.

Color in life: deep orange.

Material examined. Neolectotype. USNM 34429 , Cocos Island, Costa Rica. 5º56’ 00W N, 85º10’ 30”W. 2149 m . Col. USFCS Albatross, 1 wet spec. R=3.1, r=1.6; SIO E 1613, W. of Pta Banda , Baja California Norte, Mexico. 31º18’N, 117º37’W, 2068–2086 m, Coll. R. Parker, 13 Feb, 1960, SOB-II-5. 1 wet spec. R=3.6, r=1.5 ; USNM 1407953 D81-A11. President Jackson Seamount B. 42° 50' 3.9 N, 128° 9' 43.5 W, 1881.7 m. Coll. Dave Clague et al, MBARI-ROV Doc Ricketts Sept. 4, 2009, 1 wet spec. R=2.5, r=1.0. USNM 1407954. President Jackson Seamount C. 42° 44' 51.2, 128° 5' 30.4, 1416.5 m. Coll. Dave Clague et al, D82-A17, MBARI-ROV Doc Ricketts. 1 wet spec. R=2.8, r=1.4.

Figures

FIGURE 9. Pillsburiaster ernesti USNM 34429 Neolectotype. Scale Bar = 5.0 mm. A. Abactinal B. Close up of abactinal and superomarginal plates. C. A ctinal surface showing granulation and adambulacral accessories. USNM 1407954 D. Abactinal surface of newly collected specimen from North Pacific. E. Abactinal-lateral view arm. F. Close up of actinal surface in the oral region showing furrow spination, actinal granulation and tube feet.