Plinthaster lenaigae, 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 : 73-79

Plinthaster lenaigae n. sp.

Figure 29 A–F

Etymology. This species is named for Dr. Lenaig Hemery, crinoid researcher formerly at the Museum National d'Histoire Naturelle.

Diagnosis. A species with enlarged, triangular superomarginals adjacent to the terminal plate, and between six to eight (most with six) total superomarginals per interradius ( Figs 29A, C ). Superomarginals form prominent part of abactinal view, occupying 18–25% of the “r” distance (measured from disk center to edge of interradius ( Fig. 29A ).

Comments. Plinthaster is a widely occurring genus containing four species occurring in the Pacific, Indian and Atlantic Oceans, primarily at bathyal depths (260–2910 m). Plinthaster dentatus is a widely occurring and variable species present in the Atlantic ( Clark and Downey 1992) and apparently, New Zealand ( Clark and McKnight 2001). Plinthaster ceramoidea has been recorded from the Hawaiian Islands region ( Mah 2015). Two species, Plinthaster . investigatoris (Alcock 1893) and Plinthaster döderleini ( Koehler 1909) , have been recorded from the Indian Ocean but both species are known only from their original description. Several characters in the widespread Plinthaster dentatus vary across its range rendering direct comparisons among species occurrences difficult. Arm radii in largest-known individuals in each setting, for example range between R/r=1.0 to 1.6. Plinthaster lenaigae n. sp. differs from the more stellate Plinthaster dentatus morphotypes but shows a more similar shape similar to the pentagonal forms.

Plinthaster lenaigae n. sp. is distinct from other known species of Plinthaster in that it shows the fewest number of marginal plates (six to eight) per interradius ( Fig. 29A, C ) of all the known species, except for Plinthaster untiedtae n. sp. Plinthaster dentatus for example displays between 12 and 20 marginal plates (at R=5.5 to 7.0 cm). Similarly, both Indian Ocean species display comparably high numbers of marginal plates (17–22). The Hawaiian Plinthaster ceramoidea displays eight to ten marginal plates at R= 5.5 to 6 cm.

Also diagnostic of Plinthaster lenaigae n. sp. is the presence of an enlarged, triangular pair of superomarginal plate pair adjacent to the terminal plate. Although this character has not been observed in other Plinthaster spp. it is observed in other pentagonal goniasterids, such as Tosia australis and variably in Peltaster and Sphaeriodiscus species.

Occurrence. Madagascar and adjacent western Indian Ocean , 560–833 m.

Description. Body strongly pentagonal. R/r=1.25–1.4. Interradial arcs weakly curved ( Fig. 29A ).

Abactinal surface flat with distinctly pentagonal plate field. Individual plates weakly swollen to convex in profile; pentagonal to irregularly round or oval in outline. Largest abactinal plates at disk center and adjacent regions with smaller, more irregular shaped plates distally adjacent to contact with superomarginal plate series. Distinctly recognizable primary circlet with enlarged primary plates present interradially. Abactinal plates with 10– 45 (typically 25–35) small granules, oval to quadrate (with rounded edges) in shape, forming discontinuous but regular border surrounding each plate ( Fig. 29B ). Larger plates with greater numbers of peripheral granules proximally with smaller distal plates bearing fewer accessory granules. Each abactinal plate surface covered with 30–300 (typically 150–200) low, crystalline granules, embedded in each plate surface ( Fig. 29B ). These are present in an irregular pebbled pattern in smaller individuals (R=~2.0) but are arranged in regular rows, forming wellexpressed sunburst pattern in larger individuals (R>2.2). Crystalline granules present in relatively similar abundance on both radial and interadial regions. Shallow grooves present between plates, slightly deeper between papulae on radial regions, shallower interradially. Papulae single, present radially only, absent interradially. Madreporite, flush with abactinal surface, triagonal to hexagonal, flanked by three to five abactinal plates with well-developed sulci. Pedicellariae with paddle-like blades scattered on abactinal surface. Alveolar pits present in many cases when pedicellariae are absent.

Marginal plates form distinct pentagonal boundary of abactinal surface, comprising 18–25% of the “r” distance (measured from disk center to edge of interradius) ( Fig. 29A ). Marginal plates quadrate in outline, swollen in profile. Shallow grooves present between each plate and between marginals and abactinal and actinal plates. Superomarginals elongate, six to eight (typically six), with interradial superomarginals showing direct correspondence to inferomarginals. But with two inferomarginals slightly offset relative to enlarged subterminal superomarginal. Subterminal superomarginals prominent, swollen and enlarged, triangular in outline ( Fig. 29A, C ). Some minor variation on specimens with individual arms lacking swollen subterminals but this character is present on most arms. Inferomarginals smaller, upturned with offset plates relative to superomarginals. Terminal plate roughly pentagonal in outline with strongly pointed tip.

Superomarginals covered by 60–100 (typically 70–90) widely spaced, deciduous granules, which become more densely packed on the lateral side of the superomarginal plate surface ( Fig. 29C ). Superomarginal contact with abactinal plate surface with less abundant granules, more widely spaced. Where granules are absent, a granule-shaped, hemispherical pit is present on the superomarginal plate surface. Inferomarginals with 60–100 evenly spaced but densely packed granules. Each marginal plate with approximately 60–120 (typically about 80– 100) elongate, oval shaped accessory granules present in discontinuous but regular series around the periphery of each plate. Approximately 25 granules comprise border on each side of inferomarginal plates. Granules on actinal surface are pointed and almost spinelet-like, similar to similar pointed granules on actinal plate field. Granules on lateral surface of inferomarginals more hemispherical and similar to those on superomarginal plate surface. Pedicellariae, similar in shape to those on abactinal surface. These are not abundant and are adjacent to contact with abactinal plates.

Actinal intermediate plates present in approximately four well-defined chevrons, becoming more jumbled in arrangement distally ( Fig. 29E ). Actinal plates distinctly quadrate adjacent to adambulacral plates but becoming more irregularly polygonal in shape adjacent to inferomarginal plate contact. Actinal plates covered by abundant, evenly spaced granules. Each actinal plate with a periphery of approximately 15–50 granules, with central plate surface covered by six to 70 granules (often 20–60). Actinal granules are pointed with spinelet-like to nippleshaped tips although some are more hemispherical and rounded. Shallow grooves present among actinal platessometimes forming bisecting actinal triangular regions in half. Pedicellariae, 1–2, paddle-shaped present on actinal plate series adjacent to adambulacral plates and on some individuals at least one present on each plate ( Fig. 29F ).

Adambulacral plates approximately square to rectangular in outline, separated from other actinal intermediate plates by distinct fasciolar groove. Furrow spines, six to nine very laterally compressed, nearly foliate, quadrate to triangular in cross-section with blunt tips arranged in straight line ( Fig. 29F ). Tips of furrow spines smooth tips. Proximal-most furrow spine in series, half the length of the other furrow spines, sometimes clustering with other spinelets on adambulacral plate surface. Adjacent to furrow spines are three accessory structures, including one to two spaced conical, pointed granular spinelets (about 50–60% height of furrow spines) and a pedicellaria proximally. Pointed to angular well-spaced granules, seven to 14, present on adambulacral plate surface. Pedicellariae with valves varying from thin-paddle shaped to thick lobate present on the proximal surface of most adambulacral plate (absent on a minority of plates) ( Fig. 29D ).

Each oral plate covered by 15–24 spinelets, widely to closely spaced, thickened, quadrate to polygonal in cross-section. Six to eight (typically six) spinelets present on edges of each paired oral plate surface sitting to each side of the tissue filled gap. Proximal-most spinelets thickest, largest and abutting against spines pointing into oral cavity. Furrow spines on each oral plate, 10–12 and similar to those on other furrow spines. Those furrow spines pointing directly into mouth at oral plate tip are largest and thickest.

Color in life of this species is a light to moderate orange with a lighter yellow to straw-colored oral surface.

Material Examined. Madagascar : Holotype: IE-2013-7003 , Between Nosy-bé and Banc du Leven, 12°30'S, 48°08'E, 691–695 m. Coll. Bouchet, Puillandre & Richer, MIRIKY CP 3187 , June 26. 2009, 1 wet spec. R=2.9, r=2.2. Paratypes: Madagascar. IE-2007-1210 Madagascar , 12°51’S, 48°8’E, 592 m. Coll. Bouchet, Puillandre and Richer coll. MIRIKY, aboard N/ O Miriky 25 June 2009, 3 wet specs. R=3.2. r=2.2; R=2.6, r=1.7; R=3.2, r=2.3. IE- 2013-6953 Madagascar. Crosnier # 119, 2 dry specimens. R=3.1, r=2.2; R=3.6, r=2.6. IE-2013-7002 , Between Nosy-bé and Banc du Leven, 12°38'S, 48°10'E, 560–576 m, Coll. Bouchet, Puillandre & Richer, MIRIKY CP 3185 June 26, 2009, 1 wet spec. R=2.7, r=2.2. IE-2013-7004 Madagascar 12° 48 'S, 48° 7' E, 12° 47 'S, 48° 8' E, 782 m, Coll. MIRIKY CP 3221 , July 1, 2009. 1 wet spec. R=2.1 r=1.6. IE-2013-7005 Madagascar 12° 44' S, 48° 10' E, 12° 42' S, 48° 11' E, 624– 585 m. MIRIKY CP 3222 2 wet specs. R=2.5 r=1.7; R=2.2 r=1.3. Western Indian Ocean : IE-2013-17171 Western Indian Ocean , 12°59’S, 44 ° 56' E to 12 ° 59 'S, 44 ° 55' E, 669–692 m. Coll. S. Samadi et al. BIOMAGLO CP 4858 4.2.17.Coll. BIOMAGLO, CP 4858, 4.2.17. 1 wet spec. R=2.6 r=1.8. IE-2013-17211 Western Indian Ocean 13 ° 0 'S, 44 ° 55' E to 13 ° 1 'S, 44 ° 53' E, 742–833 m. Coll. S. Samadi et al. BIOMAGLO CP 4859, Feb. 4. 2017. 1 wet spec. R=3.2 r=2.0. IE-2013-17224 Western Indian Ocean 13 ° 0 'S, 44 ° 55' E to 13 ° 1 'S, 44 ° 54' E. 757–795 m. Coll. S. Samadi et al. BIOMAGLO CP 4856 4.2.17. 1 wet spec. R=2.2 r=1.6

Figures

FIGURE 29. Plinthaster lenaigae n. sp Holotype IE-2013-7003. R=2.9, r=2.2 cm. A. Abactinal surface.Scale bar=2.0 cm. B. Closeup of abactinal plates showing crystalline nodules.n Scale bar=0.1 cm. C. Lateral view showing superomarginal surface detail. Scale bar=0.5 cm. D. Actinal surface closeup showing pedicellariae and granules. Scale bar=0.2 cm. E. Actinal surface. Scale bar=2.0 cm. F. Closeup of furrow and adambulacral spination. Scale bar=0.2 cm.