Stephanometra tenuipinna ( Hartlaub, 1890 )

Rankin, Dana L. & Messing, Charles G., 2008, A revision of the comatulid genus Stephanometra AH Clark with a rediagnosis of the genus Lamprometra AH Clark (Echinodermata: Crinoidea), Zootaxa 1888, pp. 1-35 : 5-11

Stephanometra tenuipinna ( Hartlaub, 1890)

Antedon tenuipinna Hartlaub, 1890:178 ; 1891:54, 58, 113, pl. 3, figs. 28, 30, 34.

Himerometra tenuipinna : AH Clark, 1907:356.

Himerometra echinus AH Clark, 1908a:218.

Stephanometra coronata AH Clark, 1909b:639; 1912b:133, figs. 13 a, b; 1941:412.

Stephanometra echinus : AH Clark, 1909a:10; 1921a, pl. 15, fig. 52; 1941: 409–413, pl. 45, figs. 205–207, pl. 46, figs. 210, 211, pl. 47, figs. 212–216— Gislén, 1936:4, 5, 11, figs. 2, 2a.—AM Clark & Rowe, 1971:24.— Meyer & Macurda, 1980:85 –86, figs. 5e, 7b.— Stevens, 1989:4 –28.— Messing, 1994:239; 1998:189, 191.

Stephanometra tenuipinna : AH Clark, 1909a:10; 1941:413–415, pl. 45, figs. 208, 209.—HL Clark, 1915a:93.—AM Clark & Rowe, 1971:24.— Messing, 1998:189, 191.

Stephanometra tenuispina: Gislén, 1934:20 .

FIGURE 2. a–d. Stephanometra indica . a–c. Pinnulars typical of enlarged oral pinnules showing flat articular facets. d. Conical terminal pinnular. e–f. Lamprometra palmata , P2 pinnulars showing typically developed articular facets at ossicle ends. Scale bars: (a–b, c) 500 μm; (d–f) 100 μm.

Holotype. Antedon tenuipinna Hartlaub, 1890 , Museum für Naturkunde der Humboldt-Universität zu Berlin, cat. no. 5374, Matupi (Harbor), East New Britain, Papua New Guinea, O. Finsch, coll., (AH Clark, 1941). Holotype of Himerometra echinus AH Clark, 1908a, USNM 25442, Albatross 5147, W of Lugus I., Sulu Archipelago, Philippines, 5º41’40”N, 120º47’10”E, 38 m, 16 Feb 1908.

Material examined. MALDIVE ISLANDS: NSUOC 628, 631, 632, FLMNH 6859, 6865 (5 spec.), Nilandu Atoll, E of Madali I., Jewellers' Is., 0 2°52’6”N, 72°50’8”E, 4.5–12 m, 21 Jan 1999, DL Rankin, coll.; CRRF 51 (1), S Male Atoll Lagoon Reef, 20 m, 29 Sep 1997. PHILIPPINES: USNM 1094104, NHM 2001.6664 (2), Jesse Beasley Reef, Sulu Sea, 0 9°01'N, 119°48'E, 3–9 m, 19 Apr 1995, CG Messing, coll.; NSUOC 310, 312 (2), S end Green I., Palawan, 10°15'N, 119°30'E, 23 Apr 1995, CG Messing & C Arneson, colls.; FLMNH 6864 (1), W end S Tubbataha Reef, 0 9°49'N, 119°52'E, 21 m max., 21 Apr 1995, CG Messing, coll.; USNM 35256 (1), Albatross 5174, Candea Point, Jolo I., 0 6°03'45"N, 120°57'00"E, 5 Mar 1908; CHUUK ATOLL: USNM 1094091 (1), N side NE Pass., S of Quoi I., 0 7°31'38"N, 151°58'05"E, 9–19 m, 11 Jun 1993, P Colin, coll. MALAYSIAN BORNEO: NSUOC 256 (1), Sipadan I., 0 4°07'N, 118°38'N, 11 m, 23 Apr 1997, CG Messing, coll.; USNM 1102743 (1), E side of Mabul I., 0 4°15'N, 118°38'E, 8 m, 22 Apr 1997, CG Messing, coll.; NSUOC 304 (1), Dive Center, Mabul I., 0 4°15'N, 118°38'E, 6 m, 24 Apr 1997, CG Messing, coll. PAPUA NEW GUINEA: LACM 1991–222.1 (1), Barracuda Rock, off Pig I., Madang, 0 5°10'20"N, 145°51'53"E, 11 m, 18 July 1991, CG Messing, coll.; USNM 1093348, FLMNH 6817 (2), outside Pig I., Madang, 0 5°10'20"N, 145°51'53"E, 11–14 m, 16–18 July 1991, CG Messing coll.; IRSNB / CRI 387 (1), Platier I., Hansa Bay (NE), 20 m, 16 July 1989, MC Lahaye, coll.; IRSNB / CRI 388 (1), Pointe 0, Laing I., Hansa Bay, 25 m, 22 July 1989, MC Lahaye, coll.; IRSNB / CRI 389 (1), Mandy Passage, near Hansa Bay, 36 m, 23 July 1989, MC Lahaye, coll.

Diagnosis. A species of Stephanometra with lateral margins of brachitaxis ossicles weakly swollen or with well-rounded lateral processes oriented parallel or obliquely to ray axis (Fig. 3d–f, 7a–f). At least distal cirrals with prominent aboral spine. Pinnulars of P1-P4 and sometimes P5 elongated, LW 1.5–3.5, with reduced ambulacral groove and conical terminal segment. Proximal and distal pinnular facets with elongated triangular fossae flanking ambulacral groove.

Description. Centrodorsal discoidal or dome-shaped (Fig. 3e–f, 7g –l), 3.4–7.1 mm across, 0.9–2.4 mm high; DH 2.2–4.7. Cirri in 2–3 alternating marginal rows. Polar area small, irregular in shape, slightly concave or flat with encroaching cirri, 1.0– 4.3 mm across; D/P 1.7–3.6. Cirri XIX–XXXVIII, 23–36, 13– 31 mm long; c1–3 short; c4–8 longer than broad; c8–10 longest, LW 1.0–1.5; c9–14 and following cirrals compressed, each bearing a sharp distally directed aboral spine (Fig. 8a, b, e). Terminal claw curved, longer than penultimate cirral. Specimens from the Jewellers' Islands, Maldives, have aboral spines restricted to distalmost 1–2 cirrals (Figs. 8c–d).

Basal ossicles not visible externally; radials projecting slightly beyond edge of centrodorsal or visible in interradial angles. IIIBr2 developed only externally or both internally and externally. Ibr1 oblong, with converging lateral margins, usually free laterally but sometimes united proximally; L to 1.5 mm, W to 3.7 mm, WL 2.0–3.5, rarely less. Ibr2 (axil) with diverging lateral margins; L to 2.4 mm, W to 4.2 mm, WL 1.5–2.0, rarely less. Ray bases well separated, 1.5–2.7 mm between adjacent Ibr1. Ibr2 and IIbr1 with weak (Fig. 3e, 7a– b) to strong rounded, lateral adambulacral swellings (Fig. 3f, 7c–f). Weak adambulacral processes may be obliquely-oriented and restricted to proximal corners of Ibr2 and IIbr1, while strong processes run entire lateral length of Ibr2, IIbr1 and IIbr2. Synarthrial tubercles weakly to well-developed. Arms 22–33; R 60–185 mm. Rays most commonly with six arms each, less frequently with 2, 4, 5, 7 or 8. Br1 through br8-br10 oblong; WL ~2.0. Subsequent brachials cuneate. Br10 with W to 2.1 mm, L to 1.1 mm, WL 1.7–2.8. Syzygies at br3+4, br21+22 (infrequently br8+9, br9+10, br13+14 or br28+29). Subsequent intersyzygial interval 7–11 (less often 2–6 or 15–18). P1 through P3 or P4 and sometimes P5 stiff and spine-like, composed of cylindrical segments with ambulacrum and tube feet reduced. Pinnules on outer arms usually longer and thicker than on inner arms. First two pinnulars slightly broader than long; third and sometimes fourth slightly longer than broad; fourth and following with LW 1.5–3.5; terminal pinnular conical (Figs. 8f–s). Proximal 3–5 pinnulars laterally compressed.

P1 8.1–17.3 mm long, of 10–15 (rarely 18) pinnulars; usually slightly slenderer and shorter than P2; rarely the largest pinnule (Fig. 8f, j, o). P2 almost always the longest, thickest pinnule, 10.7–19.7 mm long, of 9–14 pinnulars; pinnular 6 with LW 1.4–3.6 (Fig. 8g, k, p). P3 4.5–13.7 mm long, of 7–12 pinnulars; sometimes as thick as P2 but always shorter; often as thick as P1 but slightly longer or shorter (Fig. 8h, l, q). P4 5.3–10.5 mm long, of 7–11 pinnulars; similar to P3 or small, weak and flexible like the following pinnules (Fig. 8i, m, r). P5 either resembling P4 or following pinnules, 3.3–7.6 mm long with 7–10 pinnulars (Fig. 8n, s). P6 and following pinnules small, weak and flexible with well-developed ambulacral groove. Subsequent pinnules gradually increasing in length. P distal 10.4 mm long with ~22 pinnulars; first pinnular broader than long; second and subsequent pinnulars longer than broad; terminal segment with small spines.

FIGURE 3. a–c. Stephanometra indica , field photographs, Lizard Island, Great Barrier Reef, Australia. a. S. indica sensu stricto, adoral view with P2 (arrows) and adjacent interior P b (orange) enlarged. b. S. indica s. s., aboral view of ray bases showing lateral tabs (arrows). c. S. indica form oxyacantha , adoral view showing numerous enlarged oral pinnules. d–f. Stephanometra tenuipinna . d. Specimen from Bay at W end of Ngerchaol I., Palau, 07º 20.483’N, 134º 25.777’E; 5.5 m. e. NSUOC-256 (preserved), with weakly developed lateral adambulacral tabs (arrows). f. NSUOC-310 (preserved), with well-developed lateral adambulacral tabs (arrows). Scale bars: (a–d) no scale recorded; (e–f) 5.0 mm.

FIGURE 6. a. Plot of aboral pole diameter against centrodorsal diameter. b. Plot of length of pinnular 6 from P2 against axil (Ibr2) width.

Color patterns. Rays variously banded with red, red-purple, maroon, orange, brown or tan and usually some white (Fig. 3d); sometimes with orange blotches; sometimes all white with red tips, or red proximally and white distally with or without red tips. At least one specimen gray proximally and deep purple distally. Brachitaxes may be orange, dark rose, purple or maroon with white, pink, orange or brown speckles, or with orange blotches or with scattered pink and white areas. The middle of the arm may be dark orange-brown with numerous white or tan bands.

AH Clark (1921b) also noted brachitaxes and arms solid dark purple, and rays alternating silver and bright red, with tips of enlarged pinnules orange. However, previously published records (AH Clark 1921b; Meyer & Macurda 1980; Stevens 1989) may be based on incorrectly identified specimens.

Distribution. On reefs from India and the Maldive Islands to Chuuk Atoll, Micronesia, and from Queensland, Australia, to southern Vietnam ( Cochinchina) and the Philippines. Previously published distributional records (AH Clark 1921b; Meyer & Macurda 1980; Stevens 1989) may be based on incorrectly identified specimens. Depth range: shoreline to 48 m.

Ecology. Cryptic during the day, curled up within the reef infrastructure or deep among the branches of Acropora colonies; emerging at night to perch on prominent coral heads. This species usually forms a biplanar arcuate filtration fan, but may also spread its arms radially over its coral perch, or raise those arms on the upcurrent side into the current, perpendicular to the substrate ( Meyer & Macurda, 1980).

Remarks. AH Clark (1941) diagnosed S. echinus as having 30–40 arms 110–170 mm long, cirri with 25– 37 cirrals, and P1-P4 stiff and spine-like, while S. tenuipinna had 16–24 arms 60–70 mm long, with 20 cirrals and P1-P3 stiff and spine-like. In fact, he suggested that S. echinus might prove to be a full-sized S. tenuipinna (p. 408). Our measurements also suggest that S. tenuipinna is simply a smaller growth stage of S. echinus , as does a series of bivariate plots of centrodorsal diameters and heights against axil width, number of cirri and maximum cirrus length ( Fig. 9 ). We thus synonymize S. echinus under the senior name S. tenuipinna . S. echinus and S. tenuipinna specimens in the current study closely resemble the holotype of Stephanometra coronata (USNM E35242) from India, which we retain within the synonymy of S. tenuipinna .

Figures

FIGURE 9. Stephanometra tenuipinna. a. Plot of number of cirri against centrodorsal height (mm). b. Plot of maximum cirrus length (mm) against centrodorsal diameter (mm).