Rhipidaster vannipes Sladen, 1889

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 : 77-80

Rhipidaster vannipes Sladen, 1889

Figure 4 A–E

Rhipidaster vannipes Sladen, 1889: 448 .

Rhipidaster (Xenorias) polyctenius Fisher, 1913: 222 .

Xenorias polyctenius: Fisher 1919: 451 .

Comments. Examination of additional specimens in comparison with the the descriptions and type material indicates synonymy of Xenorias polyctenius Fisher, 1913 with Rhipidaster vannipes Sladen, 1889 . Based on this synonymy and the occurrence of specimens, this species occurs between 167–503 m and occurs widely between the North and the South Pacific.

Characters used to distinguish between the two taxon concepts, show poor boundaries. Body ratios for example are overlapping. The R/ r ratio for the two species were described as Rhipidaster vannipes is 3.1 to 3.23 versus R/ r= 3.5 in Xenorias polytenius . Based on new specimens, R/ r shows a range of 2.44 to 4.4 with the highest and lowest R/ r ratios observed on Japanese specimens.

Furrow spines also overlap in number among individuals. Xenorias polyctenius was described as having pri- marily eight to ten furrow spines versus seven or eight in Sladen’s holotype. The Japanese specimens displayed primarily eight to ten but four up to twelve. New Caledonian specimens showed six to eight furrow spines (at R=4.1 to 4.6)

Similar characters include the distinctive enlarged, broad oral plates with a smooth, bare surface surrounding the raised “eminence” on either side of the membrane covered fossae present in each interradius between the paired oral plates ( Fig. 4D ). Arrangement of the marginal and actinal plates are in identical linear series.

Paxillae (also called pseudopaxillae in the literature) morphology is one of the few character differences between the two species. Paxillae in the holotype of Rhipidaster vannipes appear to be more elongate with four or five spinelets and free from a tissue sheath versus Xenorias polyctenius which have shorter, stouter paxillae, which are embedded in a tissue sheath bearing eight to twelve spinelets. However, individuals from other localities show overlap in numbers of paxillar spinelets. Japanese individuals show mostly four to eight (but as few or as many as two to ten) spinelets whereas individuals from New Caledonia show three to six spinelets per paxilla, all with relatively stout, short paxillar shafts. Spines on some of the New Caledonia specimens do show elongate spinelets in conjunction with the shaft, suggesting that this could be a variable character owing to collection artifact, flexibility of the spinelets, or simply naturally occurring variation of the individual while alive.

The majority of examined specimens (n=37) from Japan and New Caledonia displayed eight rays with a minority (n=8) showing seven rays and one individual from New Caledonia showing six rays. Sladen’s holotype possessed eight rays whereas Fisher’s type for Xenorias polyctenius showed seven.

Gut Content Note: Fragments from what appear to be the arms of an unidentified ophiacanthid were observed in the oral and tube foot grooves of IE-2013-12117 suggesting that the ophiuroid was being eaten. Although artificial positioning forced during trawl collection presents an alternative explanation, predation on other echinoderms would be consistent with the feeding ecology of other solasterids (e.g., Mauzey et al. 1968; Van Veldhuizen & Oakes 1981).

Occurrence: East China Sea, Japan ( Tosa Bay ), Vanuatu, New Caledonia, Molucca Islands, Torres Strait, 167– 503 m.

Description. Body stellate, arms seven or eight, interradial arcs acute. Arms thick, round in cross section. Body surface covered with thick membrane ( Fig. 4A ).

Abactinal surface forms close-set fenestrate skeleton composed of irregularly cylindrical plates arranged in a reticulate network framed around a thick membrane covering over each papular region each of one to four papulae present. Papular regions proximally with greater number of papulae with regions narrowing, decreasing to single papulae forming more close-set spaces which eventually terminate distally. Papulae present on all surfaces but absent from large distinct regions extending from abactinal to actinal surface. Reticulate skeleton covered by distinct membrane, which extends as a covering over abactinal spinelets, two to ten, mostly four to eight forming tufts on plate surfaces, especially where plates abut ( Figs. 4B, C ). Underlying paxillar base is low and round in outline. Madreporite with weakly convex to flat surface on raised plate above disk surface.

Marginal plates, 60 to 70 from arm tip to arm tip, form paired series along lateral side with a membrane-covered intermarginal region along the distance of the arm ( Fig. 4C ). Both superomarginals and inferomarginals with membrane covered, webbed spinelets, two to seven, mostly four to six in palmate curved sequence. Short membrane covered spinelets, two to four present on intermarginal surface. Superomarginal and inferomarginals arranged serially at oblique angles from one another on most, but with some, especially distal plates arranged in parallel, directly below the inferomarginals.

Adambulacral plates with four to 12 webbed, palmate, furrow spines, mostly eight to 10 on each plate, a discrete distance separates the furrow spines from two to four subambulacral spines in palmate arrangement ( Fig. 4E ). Actinal intermediate regions covered by membrane but with no other accessories other than one to four small spinelets. Oral plates with 12–14 membrane-covered spinelets; surface smooth and membrane covered. Oral plate surface enlarged, smooth, with no accessories ( Fig. 4D ). Oral plate convexities paired and covered by membrane and six to eight ensacculate spines with one enlarged spine and three to five smaller spine per side. The enlarged spine is paired its other oral plate counterpart, totaling two projecting into the moth.

Preserved specimens show mottled coloration.

Material Examined (longest arm measured). Japan. NSMT E-11341, East China Sea , 29˚0.57′N, 127˚0.40′E– 28˚58.71′N, 126˚59.55′E, 167–170 m, Coll . R / V Yoko-maru , St. 13 - T13 , 19 October 2001, 1 wet spec ., R =1.6 r=0.5, 7 arms; NSMT E-11342, Tosa Bay , 33˚13′N, 133˚37.4′E–33˚12.6′N, 133˚36.8′E, 290–293 m, Coll . R / V Kotaka-maru , St. K00-8-300, 24 August 2000, 1 wet spec ., R =3.0 r=0.8, 8 arms; NSMT E-11343, Tosa Bay , 33˚13.2′N, 133˚36.9′E–33˚10.33′N, 133˚36.2′E, Coll . R / V Kotaka-maru , St. K98-6-250, 8 June 1998, 1 wet spec ., R =36 r=10, 8 arms; NSMT E-11344, Tosa Bay , 33˚10.6′N, 133˚34.4′E–33˚10.3′N, 133˚33.9′E, 300–302 m, Coll . R / V Kotaka-maru , St. K97-11-300, 14 November 1997, 1 wet spec ., R =3.2 r=0.8, 8 arms; NSMT E-11345, Tosa Bay , ca. 300 m, Coll . R / V Kotaka-maru , 1 wet spec ., R =3.8 r=1.1, 8 arms; NSMT E-11346, Tosa Bay , 33˚13.7′N, 133˚35.9′E–33˚13.4′N, 133˚35.4′E, 177–179 m, Coll . R / V Kotaka-maru , St. K97-5-175, 14 May 1997, 3 wet specs , R =2.3 R =0.7, 7 arms, R =2.9 R =1.0, 8 arms, R =4.2 r=1.2, 8 arms; NSMT E-11347, Tosa Bay , 33˚14.0′N, 133˚38.3′E– 33˚13.6′N, 133˚38.0′E, 261–273 m, Coll . R / V Kotaka-maru , St. K99-3-250, 5 March 1999, 5 wet specs ., R =4.02 r=1.3, 8 arms, R =3.7 r=1.0, 8 arms, R =3.6 r=0.9, 8 arms, R =4.3 r=1.2 8 arms, R =4.8 r=1.3, 7 arms; NSMT E- 11348, Tosa Bay ., 33˚12.2′N, 133˚35.4′E–33˚11.8′N, 133˚35.1′E, 252–267 m, Coll . R / V Kotaka-maru , St. K97-5- 250, 16 May 1997, 2 wet specs , R =3.5 r=0.8, 8 arms, R =2.9 r=0.7, 8 arms; NSMT E-11349, Tosa Bay , 33˚13.7′N, 133˚37.3′E–33˚13.2′N, 133˚37′E, 239–258 m, Coll . R / V Kotaka-maru , St. K98-12-250, 9 December 1998, 5 wet specs , R =3.9 r=1.2, 8 arms, R =3.0 r=0.9, 8 arms, R =3.2 r=1.0, 8 arms, R =3.2 r=0.9, 8 arms, R =2.2 r=0.5, 8 arms; NSMT E-11350, Tosa Bay , 33˚14.4′N, 133˚37.5′E–33˚14.1′N, 133˚36.9′E, 198– 191 m, Coll . R / V Kotaka-maru , St. K98-6-200, 8 June 1998, 5 wet specs , R =2.2 r=0.9, 8 arms, R =3.6 r=1.3, 8 arms, R =3.6 r=1.1, 8 arms, R =3.6 r=1.1, 8 arms, R =3.8 r=1.1, 8 arms; NSMT E-11351, Tosa Bay , 33˚10.2′N, 133˚31.8′E–33˚9.7′N, 133˚31.4′E, 202–209 m, Coll . R / V Kotaka-maru , St. K97-8-200, 20 August 1997, 1 wet spec ., R =4.6 r=1.3, 8 arms; NSMT E-11352, Tosa Bay , 33˚13.1′N, 133˚36.6′E–33˚12.7′N, 133˚36.2′E, 245–248 m, Coll . R / V Kotaka-maru , St. K98-1-250, 25 January 1998, 3 wet specs , R =3.6 r=1.0, 8 arms, R =3.6 r=0.9, 8 arms, R =3.1 r=0.9, 8 arms. NSMT E-11353, Tosa Bay , 33˚13.6′N, 133˚36.4′E–33˚13.3′N, 133˚35.8′E, 198–200 m, Coll . R / V Kotaka-maru , St. K97-11-200, 14 November 1997, 6 wet specs all with 8 arms , R =1.6 r=0.5, R =1.7 r=0.5, R =1.7 r=0.4, R =2.8 r=0.9, R =4.0 r=1.4, R =3.7 r=1.3; NSMT E-11354, Tosa Bay , 33˚13.4′N, 133˚36.0′E–33˚13.1′N, 133˚35.5′E, 196–198 m, Coll . R / V Kotaka-maru , St. K97-5-200, 16 May 1997, 1 wet spec ., R =4,2 r=1.3, 8 arms; NSMT E-11355, Tosa Bay , 33˚13.6′N, 133˚36.4′E–33˚13.3′N, 133˚35.8′E, 198–200 m, Coll . R / V Kotaka-maru , St. K97-11-200, 14 November 1997, 1 wet spec ., R =3.2 r=1.0, 8 arms; NSMT E-11356, Oomurodashi Volcano , South of Izu-oshima Island, Japan, 34˚28.0′N, 139˚31.3′E–34˚28.3′N, 139˚31.6′E, 223–234 m, Coll . R / V Tansei-maru , KT-87-19, St. OM-3, 10 December 1987, 2 wet specs , R =5.3 r=1.5, 8 arms, R =4.3 r=1.0, 7 arms.

New Caledonia. IE-2007-1691 , New Caledonia, 18º57′S, 163º16′E, 460 m, Coll. P. Bouchet aboard N/O Alis, CONCALIS St. CP 2957, 2 dry specs., both with 7 arms, R =4.6 r=1.1,, R =4.1 r=1.3; IE-2013-12117 , New Caledonia, 18º54′72″, 163º23′73″, 452– 420 m, Coll. BATHUS 4, CP 928, 7 Aug 1994, 1 wet spec., R =6.5 r=1.8, 6 arms; IE-2013-5702 Grand Passage, New Caledonia, 19° 4′ 30.0036″ S; 163° 30′ 18.018″ E, 225–230 m, Coll. SMIB 6 dr. 110, 2 March 1990, 2 wet specs., R =3.0 r=1.0, 7 arms, R =1.2 r=0.3, 8 arms; IE-2007-1728 , Grand Passage, New Caledonia, 18° 58′ 6.6″ S; 163° 14′ 54.0132″ E, 432–448 m, Coll. CONCALIS CP 2958, 1 wet spec., 7 arms, R =1.9 r=0.5.

Vanuatu. IE-2013-12848 , N Malekula, Vanuatu , 15° 50′ 17.3976″ S; 167° 17′ 28.8096″ E, 207–280 m, Coll. N /O Alis, 5 October 1994, 4 dry specs., 7 arms , R =1.7 r=0.5, R =1.4 r=0.3, R =0.8 r=0.2, R =0.7 r=0.2; IE-2013-8345 , N Malekula, Vanuatu , 15° 50′ 17.3976″ S; 167° 17′ 28.8096″ E, 207–280 m, Coll. N /O Alis 5 October 1994, 2 dry specs .

Arafura Sea. NHM 90.5.7.706, Holotype, Between Cape York and Frederick Henry Island, 51.2 m (28 fms) HMS Challenger St. 188, Coll. 10 September 1874, 1 wet specimen R =8.5 r=2.7.

Figures

FIGURE 4. Rhipidaster vannipes NSMT E-11351. A. Abactinal surface. Scale bar=0.5 cm. B. Close-up of abactinal surface on holotype (NHM 90.5.7.706) of Rhipidaster vannipes. Scale bar=1.0 cm. C. Arm showing marginal plate series. Scale bar=1.0 cm. D. Oral surface. Scale bar=0.5 cm. D. Tube foot groove showing adambulacral plates and furrow spination. Scale bar=1.0 cm.