Lophaster cactorum, Mah & Fujita, 2020

Mah, Christopher L. & Fujita, Toshihiko, 2020, New species and occurrence records of Japanese Solasteridae and Ganeriidae including a new species of Paralophaster from the North Pacific with an overview of Hyalinothrix, Zootaxa 4750 (1), pp. 67-100 : 71-73

Lophaster cactorum n. sp.

Figure 2 A–E

Etymology: The species epithet is derived from the Latin cactus, the prickly plant, alluding to the many furrow spines and the high number of paxillar spinelets.

Diagnosis. A stellate to strongly stellate species (R/r=2.7–4.7), arms round, strap-like in outline, interradial arcs moderate. Actinal surface flattened. Abactinal paxillae with 6–50, mostly 20–40 fine glassine spinelets, each with 2–4, fine hyaline tips. Approximately 40 paxillar marginal plates per interradius (arm tip to arm tip), enlarged relative to the adjacent abactinal paxillae. Each marginal with a tuft of 10–30, mostly 15–20 spinelets with 1–2 fine glassine tips. Actinal plates primarily on disk, extending partially along arms. Actinals each covered with small hyaline spinelets with fine tips. Furrow spines, 5 to 9 (mostly 7 or 8), webbed, decreasing from 9 to 5 proximal to distal. Subambulacrals 3 or 4, with serrated edges.

Comments. Lophaster cactorum n. sp. is distinguished from other species in having seven to nine furrow spi- nes per adambulacral plate (at R=2.8–3.0) ( Fig. 2E ), which is the highest number of furrow spines known for the Japanese species. Other Lophaster species possess fewer furrow spines (n=2 to 6 for comparable R of 2.8 to 3.0). This species also displays a large number of fine paxillar spinelets (20–40) relative to other Japanese species.

Occurrence: Southwestern Japan, 293–1181 m

Description. Body stellate to strongly stellate (R/r=2.7–4.7), arms round, weakly convex in cross-section, strap-like in outline. Interradial arcs moderate. Actinal surface flattened ( Fig. 2A ).

Abactinal skeleton reticulate composed of paxillar plates ( Fig. 2B ) with three lobate processes emerging from the base, articulating with adjacent paxillae. These create open network covered with an opaque membrane, through which one to four large papulae emerge. More distal plates, less reticulate becoming more flattened and imbricate. Papulae are most abundant proximally on the disk bearing up to four (R up to 3.0) but decreasing to single papulae proximally on the arms, then disappearing completely on the distal half of the arms. A prominent interradial region on the disk is devoid of papulae but not of paxillae and is composed of denser skeleton with fewer open regions. These interradial areas are directly associated with large, primary, paxillar plates on the disk ( Fig. 2C ). Paxillae widely spaced, each with six to 50, mostly 20–40 fine, glassine spinelets with two to four fine hyaline tips. Madreporite polygonal, convex sitting on the apex of the bare interradial region adjacent to one of the primary plates. No pedicellariae.

Marginal plates, approximately 40 per interradius (arm tip to arm tip), both superomarginal and inferomarginal plates paxillate ( Fig. 2C ), each plate enlarged, approximately six to eight times the size of adjacent abactinal plate. Large cylindrical base for each plate, each paxillae with a tuft of 10–30, mostly 15–20 fine hyaline spines each with single or two point glassine tips. Superomarginals and inferomarginals with one to one correspondence but with each plate directed away from the other ( Fig. 2C ); distinct gap between the two, shape round in outline. Inferomarginal plate with a larger, thicker tuft of fine hyaline spines, 10 to 50, mostly 20 to 40, almost quadrate in outline. No intermarginal papulae present between marginals. Both superomarginal and inferomarginal paxillae widely spaced from one another. Surface between marginal paxillae is smooth and barren of accessories. Paired marginal plates in contact at the center of the interradius.

Actinal plates round, bulbous, arranged in widely spaced, ordered chevron-like series ( Figs. 2D, E ), extending from disk approximately 70% of the arm distance before “pinching out.” Each plate covered by small, hyaline spinelets each with one or two glassine tips, numbering 10 to 40, mostly 20 to 30, alternating with subambulacrals on each adambulacral plate. Well developed fasciolar channels between plates.

Adambulacral plates separated by tissue between plate contacts. Furrow spines webbed, five to nine, but mostly seven or eight, with nine spines proximally decreasing to five distally ( Fig. 2E ). Furrow spines form convex fan-like array with webbing present over 50% of the distance between spines. Subambulacral spines, three or four, mostly three with serrated edges, all centered adjacent to the furrow spine on each adambulacral plate. Oral plate with 12 webbed furrow spines, identical to those on adambulacral plates and one spine per oral plate directed into the mouth (thus, two total per interradius). Oral plates, strongly convex with one to four small round spiny round plates similar to those on the actinal surface covered by micro-spination, total cover numbering up to 15 spinelets.

Tube feet well-developed, groove is wide. Color of living specimens shows it to be a dark brown with white marginal paxillae.

Material Examined. Holotype. NSMT E-11325, Off Cape Toi-misaki , Miyazaki Prefecture, Japan, 31˚07.9284′N, 131˚39.0357′E, 31˚06.6968′N, 131˚39.0302′E, 1063–1082 m, Coll. R / V Tansei-maru, KT-11-12, St. T10-2 , 23 June 2011, 1 wet spec., R =3.1 r=0.8.

Paratypes. NSMT E-11326, Off Cape Daio-saki , Wakayama Prefecture, Japan, 34˚05.9′N, 136˚40.8′E– 34˚05.9′N, 136˚38.7′E, 422–425 m, Coll . R / V Tansei maru, KT-86-6, St. KN 4, 27 May1986, 1 wet spec ., R =4.8 r=1.2; NSMT E-11327, Off Tanabe , Wakayama Prefecture, Japan, 33˚35.49′N, 135˚10.33′E–33˚35.44′N, 135˚08.00′E, 322–346 m, Coll . R / V Tansei-maru , KT-84-12, St. 27, 2 September 1984, 1 wet spec ., R =2.9 r=0.8; NSMT E- 11328, Tosa Bay , Japan, 33˚10.8′N, 133˚38.1′E–33˚10.4′N, 133˚36.9′E, 408–413 m, Coll . R / V Kotaka-maru , K98- 6-400, 29 June 1998, 1 wet spec ., R =2.8 r=0.9; NSMT E-11329, Tosa Bay , Japan, 33˚12.5′N, 133˚38.6′E–33˚12.2′N, 133˚38′E, 364–382 m, Coll . R / V Kotaka-maru , K99-9-400, 27 September 1999, 1 wet spec ., R =2.6 r=0.8; NSMT E-11330, West of Heda , Suruga Bay, Japan, 34˚46.64′N, 138˚41.86′E–34˚47.17′N, 138˚40.86′E, 349–542 m, Coll . R / V Seisui-maru, CT 95-4, St. CT4, 5 October 1995, 1 wet spec ., R =4.3 r=0.9; NSMT E-11331, East of Cape Taitosaki , Boso Peninsula, Japan, 35˚05.225′N, 140˚51.8357′E to 35˚04.273′N,140˚ 50.876′E, 971–1011 m, Coll . R / V Tansei-maru , KT-03-17, St. TS 6-5, 18 November 2003, 4 wet specs ., R =2.8 r=0.8, R =2.7 r=0.1, R =2.9 r=0.9, R =2.6 r=1.3; NSMT E-11332, West of Matsuzaki , Suruga Bay, Japan, 34˚46.7′N, 138˚41.4′E–34˚47.7′N, 138˚42.7′E, 405– 457 m, Coll . R / V Tansei-maru , KT-79-11, St. OT-4, 19 July 1979, 1 wet spec ., R =3.7 r=1.0; NSMT E-11333, Tosa Bay , Japan, 33˚11.982′N, 133˚37.936′E–33˚12.356′N, 133˚38.124′E, 370–380 m, Coll . R / V Kotaka-maru , K98-9- 400(2), 8 September 1998, 1 wet spec ., R =1.5 r=0.4; NSMT E-11334, Southeast of Tokachi , Hokkaido Prefecture, Japan, 42˚15.84′N, 144˚05.24′E–42˚16.53′N, 144˚05.68′E, 992–1042 m, Coll. KT-90-8, St. KR 09, 14 June 1990, 1 wet spec ., R =3.5 r=0.8; NSMT E-11335, 32˚32.9′N, 132˚27.2′E–32˚33.0′N, 132˚29.7′E, 1090–1091 m, Coll . R / V Tansei-Maru , KT-86-16, St. C, 2 November 1986, 3 wet specs ., R =2.7 r=0.8,, R =2.1 r=0.5,, R =4.6 r=1.4; NSMT E-11336, Kumano Sea, 33˚54.556′N, 136˚50.292′E–33˚55.279′N, 136˚49.391′E, 1165–1181 m, Coll . R / V Tansei- Maru , KT-88-15, St. KN 17, 21 August 1988, 1 wet spec ., R =3.3 r=1.2; NSMT E-11337, South of Tanegashima Island , Kagoshima Prefecture, Japan, 29˚58.99′N, 130˚57.13′E–29˚59.41′N, 130˚58.59′E, 993–1031 m, Coll . R / V Tansei Maru , KT-97-2, St. YT-6(2), 17 February 1992, 1 wet spec ., R =3.3 r=0.8; NSMT E-11338, Tosa Bay , Japan, 33˚12.3′N, 133˚36.5′E–33˚12.6′N, 133˚37′E, 293–300 m, Coll . R / V Kotaka-maru , K97-5-300, 16 May 1997, 1 wet spec ., R =1.9 r=0.5, 6 arms.

NSMT E-11339, Tosa Bay , Japan, 33˚13.2′N, 133˚40.1′E–33˚13.6′N, 133˚40.6′E, 397 m, Coll . R / V Kotakamaru, K 00-5-400, 9 May 2000, 1 wet spec ., R =3.0 r=0.8.

Figures

FIGURE 2. Lophaster cactorum n. sp. Holotype, NSMT-E-11325.A.Abactinal surface. Scale bar=1.0 cm. B. Abactinal surface closeup showing paxillae. Scale bar=0.5 cm. C. Lateral view showing marginal paxillae. Scale bar=0.5 cm. D. Actinal surface. Scale bar=1.0 cm. E. Oral region. Scale bar=0.5 cm.