Sphaeriodiscus biomaglo, 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 : 82-84

Sphaeriodiscus biomaglo n. sp.

Figure 31 A–E

Etymology. This species is named the BIOMAGLO expedition, during which this species was discovered. Noun held in apposition.

Diagnosis. A species distinguished by its enlarged, triangular penultimate superomarginal plates, twelve superomarginals per interradius and three or four furrow spines.

Comments. This species most closely resembles New Zealand species documented by H.E.S. Clark and McKnight (2001), including Sphaeriodiscus irritatus and Sphaeriodiscus maui , both of which have similar relatively square to quadrate superomarginals and triangular superomarginals adjacent to the terminal plate. Sphaeriodiscus biomaglo n. sp. is closer in overall morphology to Sphaeriodiscus maui sharing a similar number of interradial superomarginal plates in comparably sized specimens (n= 12 in S. biomaglo vs. n= 10 in Sphaeriodiscus maui ) and a nearly identical pre-terminal, triangular superomarginal plate ( Fig. 31A ). However, Sphaeriodiscus biomaglo n. sp. has fewer furrow spines (four to seven vs. eight to ten in S. maui ) and displays hexagonal carinal plates rather than the elongate, “kite-shaped” carinal plates indicated of S. maui .

Occurrence. Mayotte Island region , western Indian Ocean. 388–505 m.

Description. Body stout, pentagonal (R/r=1.2–1.5) in outline. Interradial arcs weakly curved to straight ( Fig. 31A, D ).

Abactinal surface flat. Abactinal plates polygonal, those in radial regions displaying numerous plates hexagonal in outline with plates becoming more irregularly polygonal and smaller distally, adjacent to superomarginal contact ( Fig. 31B ). Plates along radial regions displaying shallow fasciolar grooves, papulae present around each plate, six. Fasciolar grooves and papulae absent interradially. Abactinal plate surface covered by granules, 10–200 per plate, flat-topped polygonal to round, coarse, approximately three counted along a 1.0 mm line, all evenly arranged on surface. Peripheral granules, seven to 60 in a single close but evenly distributed series. Plates along radial regions with more heavily accentuated peripheral granules, 10–30, which are more strongly trapezoid-like in shape, differing in shape from those granules on plate center. Smaller individuals (R=2.5) with more homogeneous peripheral granules around each plate. Plates on interradial and central disk, polygonal to round, more homogeneous and more closely resembling granules on center region of each plate. Central granules coarse, flat-topped, round but evenly distributed, approximately five along a 1.0 mm line. Small, 1.0 mm long paddle-shaped pedicellariae on plates adjacent to the superomarginal contact. Madreporite triangular, flanked by three to four plates.

Superomarginal plates ten, inferomarginal plates 12 on specimen with R= 3.3 cm. Smaller individual, at R= 2.5 cm with eight superomarginal and inferomarginals ( Fig. 31A, D ). Superomarginals and inferomarginals mostly with 1:1 correspondence but slight offset distally. Superomarginals wide, quadrate in outline, relatively flat surface, flush with abactinal surface. Penultimate superomarginals enlarged, triangular, ( Fig. 31C ) with lateral edge in full contact along arm midline but not disproportional to other superomarginals. Superomarginal plate surface each with large, quadrate-shaped, weakly convex bald patch, mostly smooth and bare save for five to 15 (mostly eight to 10) widely spaced, coarse granules. Remainder of superomarginal plate surface covered by close, densely packed clusters of coarse granules, approximately 100–400 (mostly 200–300) per plate, covering surface adjacent to contact with abactinal plate surface and lateral side with inferomarginal plates. Granules, five to six counted along a 1.0 mm line. Peripheral granules in a single, closely set series around the edge. Inferomarginal surface of specimen with R=3.3 entirely covered by granules, five or six along a 1.0 mm line, approximately 200–500 per plate surface. Smaller R=2.5 specimen with small quadrate bare spots on actinal surface of inferomarginals, each bearing small coarse granules, widely spaced. Small 1.0 mm long pedicellariae with paddle-shaped valves present on inferomarginal plate’s actinal face adjacent to actinal plate surface. Terminal plate weakly convex, triangular in shape. Bare surface.

Actinal surface composed of five full series of quadrate to polygonal plates with one or two irregular/ incomplete series adjacent to inferomarginal plates at R= 3.3 cm ( Fig. 31D ). Smaller specimen (R= 2.5 cm) with approximately three full series but with more irregular round to polygonal shapes. Coarse, homogeneous granules,15–40, round to polygonal in shape, cover each plate surface. Approximately four granules along a 1.0 mm line, distributed evenly along the plate surface. Peripheral granules, 15–20, slightly more angular/quadrate in shape then central granules, which are more round. Pedicellariae small, with elongate, narrow paddle-shaped valves, approximately 1.0 mm in length seated in pits centrally located on approximately 40–50% of actinal plates, especially those distally adjacent to the inferomarginals.

Furrow spines four to seven, blunt tipped, oval to quadrate in cross-section in weakly palmate to straight series ( Fig. 31E ). Smaller individual (IE-2013-17185 at R= 2.5 cm) with four to six, mostly four spines. Discrete space between furrow spine and first subambulacral spine series. Subambulacral spines, two to four, mostly three per adambulacral plate, each spine twice as thick as each furrow spine. The smaller IE-2013-17185 with no pedicellariae on adambulacral plates, two or three, round, thick bulbous subambulacral spines on first five adambulacral plates. First four to five adambulacral plates with large central subambulacral round and enlarged, twice as thick as furrow spines, with one peripheral granule/spines half the length of the furrow spines on the distal side, and one pedicellaria-tong-like with two narrow valves present on the proximal side. Remaining surface of adambulacral plate surface with 10–15 angular adambulacral granules, short similar in morphology to those on actinal plate surface. Oral plate with 12 blunt furrow spines, blunt, oval to quadrate in cross-section. Tip of each oral plate with one spine, round, blunt tipped and triangular in cross-section for each half, so two on the apex of each oral plate. Remainder of oral plate armature set off by discrete bare surface on oral surface. Angular, granules, approximately nine or 10 for each side of the sulcus bisecting the center of the oral plate. Short granules, nine or ten, angular to quadrate in outline, covering the oral plate surface.

Color in life: Overall orange with deep-red bands present interradially.

Material Examined. Holotype IE-2013-17197 , Western Indian Ocean. 12° 23' S, 43° 33' E to 12° 23' S, 43° 33' E, 420– 388 m. Coll. Samedi et al. BIOMAGLO DW 4842 , Jan 29 2017. 1 wet spec. R=3.3 r=2.2 . Paratypes IE-2013-17185 , Off the southeast coast of Mayotte Island, 12° 56'S, 45° 15' E, 474–505m, Coll. S. Samadi, BIOMAGLO DW 4865 , Feb 7, 2017. 1 wet spec. R=2.5 r=1.6

Figures

FIGURE 31. Sphaeriodiscus biomaglo n. sp. Holotype IE-2013-17197. R=3.3, r=2.2 cm. A. Abactinal surface. Scale bar=1.0 cm. B. Closeup showing abactinal plates and granulation. Scale bar=0.5 cm. C. Arm tip and superomarginal plate surface. Scale bar=0.5 cm. D. Actinal plate surface. Scale bar=1.0 cm. E. Closeup of furrow and adambulacral spination. Scale bar=0.3 cm.