Astroceramus eleaumei, Mah, 2018

Mah, Christopher L., 2018, New genera, species and occurrence records of Goniasteridae (Asteroidea; Echinodermata) from the Indian Ocean, Zootaxa 4539 (1), pp. 1-116 : 11-12

Astroceramus eleaumei n. sp.

Figure 3 A–G

Etymology. This species is named for echinoderm researcher and colleague, Dr. Marc Eléaume at the Museum national d'Histoire naturelle.

Diagnosis. A species distinguished by abactinal plates extending to slightly more than 50% of the arm distance ( Fig. 3B ). Arms elongate with stellate body form (R/r=3.2–4.1) ( Fig. 3A,B, F ). Furrow spinesfour or five with two thickened subambulacral spines ( Fig. 3E ).

Comments. This species shares closest similarity with Astroceramus kintana n. sp. with which it shares the presence of the abactinal plates along the proximal half of the arm distance ( Fig. 3B ).

Abactinal arm plates in this species are wide ( Figs. 3A, B ) relative to those in Astroceramus kintana n. sp., which has more elongate arm plates and seven or eight furrow spines. Relatively small individuals of this species display the abactinal arm plate/abutted superomarginal plate character at R= 1.2 cm.

This species and Astroceramus kintana are closely related and are likely sister species.

Occurrence. Madagascar, 331–491 m

Description. Body stout, flat, strongly stellate in shape (R/r=3.2–4.1) with arms elongate, triangular. Interradial arcs acutely curved ( Figs 3A, B, F ).

Abactinal surface flat, flush with superomarginal plate series which forms a distinct, dorsal-facing border when viewed from above. Abactinal plates diamond to pentagonal to nearly round in outline. Plates largely homogeneous in size, shape but are more irregular in shape adjacent to the superomarginal contact. Carinal series extends from disk to 40–70% of arm distance with individual plates becoming wider than long as they approach arm. Plates on arm narrow to a single row with oval to elliptically shaped (i.e. wider than long with rounded edges) along arm as space between superomarginal plates narrows. Some plates occur along arm midline between contacts on superomarginal midline ( Fig. 3B ). Abactinal plates on distal regions of arm are smaller, more irregular in size and lacking crystalline bosses present on more proximal plates (described below).

Disk plates smooth, bare with no surficial granulation or other accessories other than pedicellariae. Peripheral granulation, 20–50 in number, approximately five granules present per side. Each plate with 2-200 inset, crystalline bosses inset into the surface of each plate with larger plates bearing greater numbers of bosses ( Fig. 3C ). Fewest number of bosses are present on plates present along carinal ridge on arm mid-line. Papulae four to six per plate, present in each corner. Papular regions radial, absent interradially. Madreporite triangular, in shape, flanked by three abactinal plates in specimens observed for the type series, with relatively few, deep sulci. Anus located centrally, flanked by four plates. Pedicellariae with two paddle-shaped plates occurring irregularly on disk surface.

Marginal plates elongate, quadrate in outline. Superomarginal and inferomarginal plates correspond 1:1 interradially becoming more offset distally along arms. Approximately 32–40 superomarginals present per interradius (arm tip to arm tip). Superomarginals abut over midline at approximately 50–70% of arm distance ( Fig. 3B ). Abutting is gradual with abactinal disk plates forming triangular inset onto arm, gradually pinching out with plates discontinuously separated by superomarginals in contact. Superomarginals on disk, number from 12 to 24 (or six to 12 if counted from the midline) per interradius as counted from arm to arm at the last point where plates remain in continuous contact meeting first abutting superomarginals. Superomarginals elongate adjacent to terminal. Segment of superomarginals sharing disk facing bare and smooth. Dorsolateral to lateral surfaces of superomarginals with large, coarse, round granules, 5–30. Greatest number of granules present interradially with fewer along arm, gradually disappearing at tip. Granules when absent, leave distinct concave pitting on surface. Peripheral accessories include approximately 20–30 round, coarse granules per side. Pedicellariae similar to those on the abactinal plats present on one to two superomarginal plate surfaces on abactinal disk side. Inferomarginals 38–44 from arm tip to arm tip (fewer than superomarginals). Surface bare, smooth save for large, round granules, four to 20 on ventral facing. Some granules sit on raised convexities. Absent granules leave concave pitting. Paddle-shaped pedicellariae also present on inferomarginal surface ( Fig. 3D ). Inferomarginals with 10–15 peripheral granules per side.

Actinal surface composed of three to four chevron shaped series ( Fig. 3F ). Plates quadrate in shape each with coarse, round granules, 9–15 forming periphery around edges. Plate surfaces are smooth, bare with no surficial coverings other than for single tubercles and pedicellariae, which occur on numerous plates proximally adjacent to the adambulacral plate series and near the oral region ( Fig. 3G ). Pedicellariae two or exceptionally three valves laying flush in alveolar pits on plate surface.

Furrow spines four or five, strongly flattened with rounded, blunt tip all similar in length. Subambulacral spines two, round in cross-section, with blunt tips present adjacent to furrows, but separated by a brief space ( Fig. 3E ). Subambulacrals three to four times as thick as furrow spines. Distal subambulacral spine two to three times as long as proximal subambulacral, at least proximally. More distal spines similar in length. Second row of subambulacrals composed of two to three shortened spines similar in length to peripheral granules on actinal plates. Oral plates with similar furrow spines, four to six. Oral plate surfaces with seven to nine spines, quadrate to triangular in cross-section with blunt, pointed tips. Smaller distally becoming larger proximally ( Fig. 3G ).

Based on deck photos, this species is a deep red-orange in life.

Material Examined: Holotype: IE-2007-1067 . Madagascar 12°30’S, 48°18’E, 376 m. 1 dry spec R=6.3, r=1.7. Paratype: IE-2007-1009 Madagascar 12°58’S 47°58’E, 1200 m, Coll. Bouchet, Puillandre & Richer , MIRIKY CP 3218 . 1 wet spec. R=5.5 r=1.5 (arms broken) , IE-2007-1043 entre Nosy-bé et Banc du Leven, Madagascar 12°44’S, 48°12’E, 442– 491 m. 1 wet spec R=6.6, r=1.6; IE-2013-12591 (ex. 1094). entre Nosy-bé et Banc du Leven, Madagascar 12°46'S, 48°11'E, 430–488 m , Coll. MIRIKY CP 3223 (1 wet spec. R=5.4, r=1.7) ; IE-2013-12592 (ex 1059) entre Nosy-bé et Banc du Leven, Madagascar 12°36'S, 48°16'E, 331– 364 m. (1 wet spec. R=5.0, r-1.5).

Figures

FIGURE 3. Astroceramus eleaumei n. sp. Holotype IE-2007-1067. R=6.3, r=1.7 cm. A. Abactinal surface. Scale=1.5 cm. B. Close up of arm tip showing abactinal plates. Scale=0.5 cm. C. Closeup of abactinal plates showing crystalline nodules. Scale=0.1 cm. D. Superomarginal plate surface showing pedicellariae. Scale=0.2 cm. E. Furrow spines and adambulacral spination. Scale=0.2 cm. F. Actinal surface. Scale=0.15 cm. G. Closeup of oral region. Scale=1.0 cm.