Astroceramus pernachus, Mah, 2026

Astroceramus pernachus View in CoL sp. nov.

FIGURE 18A–F View FIGURE 18

Etymology

This species is named for a pernach , a type of flanged mace alluding to the distinctive shape of the subambulacral tubercle.

Diagnosis

Body stellate (R/r=2.27–2.52), arms elongate and triangular, interradial arcs straight to weakly curved. Abactinal plates largely limited to disk with short single series extending proximally onto arms. Superomarginals, 5–7 abutted, superomarginal plates 12–13 free on disk. covered on abactinal-lateral surface with 30–50 widely spaced granules. Actinal plates covered by granules, coarse, round. Furrow spines, 7–8, distinct single subambulacral tubercle with denticulate surface.

Comments

Astroceramus pernachus sp. nov. is distinguished by the single denticulate subambulacral spine ( Fig. 18F View FIGURE 18 ), but also its relatively short, triangular arms and stellate shape ( Fig. 18A View FIGURE 18 ). Other New Caledonian species are either much more stellate, such as A. callimorphus which displays elongate, slender arms and 2 to 3 thick subambulacrals or much more compact, such as A. cyclus sp. nov. or A. astrikos sp. nov. which display short or no distinct arms. Astroceramus eldredgei shares a similar type of single, enlarged subambulacral tubercle but displays much fewer, thicker furrow spines and larger, thicker superomarginal plates and shorter arms.

Occurrence/Distribution

Known only from New Caledonia, 600–691 m.

Description

Body stellate (R/r=2,.27–2.52), arms elongate and triangular, interradial arcs straight to weakly curved ( Fig. 18A, E View FIGURE 18 ). Abactinal surface sunken relative to superomarginal frame.

Abactinal plates distinct in shape, hexagonal to round in outline, present only on disk, ending where superomarginals abut on arms ( Fig. 18A, C View FIGURE 18 ). Plate surface smooth, bare with no surficial accessories (i.e.,no granules, etc.). Glassy granules, 15–35, mostly 20–25, embedded in abactinal plate surface. Highest glassy granule abundance centrally on disk, with plates in contact with interradial superomarginals devoid of glassy granules ( Fig. 18A, C, D View FIGURE 18 ). Abactinal plates homogeneous in size, even at distal contact with superomarginal plates with only a few plates smaller and more irregular in size, shape. Each abactinal plate with 10–18 widely distributed bead-shaped granules evenly spaced on each side, (3 granules on each side in most). Madreporite, convex, trapezoid in shape, flanked by four abactinal plates ( Fig. 18B View FIGURE 18 ). Anus flanked by approximately 12 granules, six of which are approximately twice the size of the granules observed around the other plates. Four of the five inter radii with one or two strongly convex, plates devoid of glassy granules, irregularly located on the contact between the superomarginals and the abactinal surface. No pedicellariae.

Superomarginal and inferomarginal plates, 27to 29 per interradius, with 11–12 superomarginals abutted over mid-radius and encompassing total arm distance ( Fig. 18A, E View FIGURE 18 ). Superomarginal plates wide, forming distinct peripheral border when viewed on abactinal surface. Individual plates strongly arched in cross-section. Superomarginals along arm forming flattened surface on abactinal surface on three of the five rays. Two distal arm tips show irregular correspondence and could be damaged ( Fig. 18C View FIGURE 18 ). Surface of all marginal plates, especially those proximally with rugose texture, with regular, almost molar-like patterns but then becoming more flattened distally. Superomarginals with no granules on abactinal surface but with 20 to 60 (mostly 30 to 50) deciduous, round granules present along abactinal-lateral edge in a roughly rounded quadrate patch on each plate ( Fig. 18D View FIGURE 18 ). Surface around this patch is smooth and devoid of granules or other accessories. Marginal plates each surrounded by approximately 30 to 120 round granules. Inferomarginals further covered by abundant round granules, approximately 30 to 200 (mostly 50 to 160) in close-set dense arrangement especially along ventrolateral edge of inferomarginal plates. Inferomarginal actinal surface with irregularly shaped but prominent bald patch.Terminal plate, round,smooth approximately the size of four adjacent superomarginal plates. No pedicellariae.

Actinal surface large with three full series in chevron-like series with one irregular series adjacent to the inferomarginals interradially ( Fig. 18E View FIGURE 18 ). Actinal plates flat, covered by abundant, coarse, round granules, approximately three counted along a 1.0 mm line, and 15 to 25 widely spaced on the surface of each plate.Actinal plates mostly quadrate becoming more irregular in shape distally, adjacent to inferomarginals. Five small, approximately 1.0 mm in length, paddle-shaped pedicellariae with valves displaying rough edges on each tip.

Furrow spines, 7or8,flattened, with round tips, paddle-shaped, in a straight to weakly curved array. Spines thicker proximally, becoming thinner distally. Proximalmost furrow spines approximately 25% of the height of the other spines. Furrow spines set off from subambulacral spine by discrete bald space. Subambulacral accessories composed of a pedicellariae with elongate, round-tipped forceps like valves showing smooth edges and one very enlarged and thick blunt spine or tubercle, approximately 3 to 5 times the thickness of the furrow spines and approximately twice the length ( Fig. 18F View FIGURE 18 ). Remaining accessories on adambulacral plates composed of 6 to 10 large tuberclelike granules, similar to but slightly larger than granules on actinal plate surface.

Oral plate with eight to ten thick furrow spines along edge of plate with one prominent oral spine directed into mouth (two total) from each oral plate half. Each spine quadrate in cross-section with round tipped edge. Oral plate with one prominent spine identical to subambulacrals present on other plates, and three thick spines on each plate, paired with a corresponding spine on the other half, making six total. Remainder of oral plate surface with coarse, widely spaced blunt granules. Approximately 8 on each paired side of the oral plate.

Material Examined

Holotype. MNHN IE-2013-7013 , New Caledonia, 24°40'S, 168°38'E, 600 m, Coll. NORFOLK 2, DW 2060 , 25 Oct 2003. 1 dry spec. R =4.6 r=2.1. GoogleMaps

Paratype. MNHN IE-2013-4710 , Banc Athos , New Caledonia, 25°16'35.4036"S, 168°55'38.4168"E, 609– 691 m. Coll. NORFOLK 2 GoogleMaps , DW 2064 , 26.10 .03. 1 wet spec. R =5.8 r=2.3 .

MNHN IE-2013-7040 New Caledonia, 23°37.81'S, 167°38.78 E, 571–610 m. Coll. NORFOLK 2 GoogleMaps , DW 2036 . 1 dry spec. R =7.5 r=3.3 .