Atelecrinus helgae

Messing, Charles G., 2013, A revision of the genus Atelecrinus PH Carpenter (Echinodermata: Crinoidea), Zootaxa 3681 (1), pp. 1-43 : 12-15

Atelecrinus helgae AH Clark, 1913

Figure 6

Atelecrinus helgae AH Clark, 1913:4; 1923:44.— Gislén, 1924: 43, 45, 47, 50, 53, 81, 83, 93.— Mortensen, 1927: 22 –23.—AH Clark and AM Clark, 1967: 819, 831–832.

Atelecrinus balanoides : AM Clark, 1970: 49 –51 (part).

Atelecrinus balanoides form helgae: Messing and Dearborn, 1990: 11 , 23.

Holotype. USNM 35779, Helga 120, NW of Galway Bay, Ireland, 53º58’N, 12º24’W, 698 m, 24 Aug 1901 (1).

Other material examined. Northeastern Atlantic: ZMK (no catalogue or station number), Thor , SW of Faeroe Is., 61º15’N, 09º35’W, 900 m, 22 May 1904 (2 spec.). Gulf of Mexico: TAMU 3-0727, Alaminos 68A13-12A, 25º31’N, 95º51’W, 17 Nov 1968, 1061– 1317 m, WE Pequegnat, coll. (1); TAMU 3-0752, Alaminos 69A11-7, 27º01.3’N, 94º43.5’W, 7 Aug 1969, 1400 m, WE Pequegnat, coll. (1); NSUOC CRI-496, MMS-NGOMCS sta. WC12, sample 5509-1, 27º19’37”N, 91º31’21”W, 1170–1236 m, 13 Jun 1985, LGL, coll. (1); USNM E41942 , Citation CO8, SW of Grand Island, LA, 27º31’04”N, 89º48’56”W, 15 Nov 1984, 1064 m (2). Blake Plateau: USNM 34956, Albatross 2415, off NE Florida, 30º44’N, 79º26’W, 1 Apr 1885, 805 m (1); USNM E19291 , Gerda 182, N of Little Bahama Bank, 27º55’N, 78º40’W, 2 Jul 1963, 860– 897 m (1); USNM E19285 , Gerda 403, N of Little Bahama Bank, 27º49’N, 78º50’W, 20 Sep 1964, 824 m (1). Strait of Florida: USNM E17879 , Pillsbury 636, SE of Key West, 23º54’N, 81º27’W, 25 Mar 1968, 1003– 1336 m (2); USNM E19282 , Gerda 130, W of Cay Sal Bank, 23º59’N, 81º10’W, 21 Jun 1963, 1021 m (1); USNM E19283 , Gerda 374, S of Key West, 23º50’N, 81º37’W, 17 Sep 1964, 1208– 1241 m (2); UMML 44.180, Gerda 448, NE of Havana, 23°54’N, 82°21’W, 1135–1184 m, 1 Dec 1964 (2). USNM E19290 , Gerda 963, NE of Havana, 23º41’N, 82º16’W, 1 Feb 1968, 1441– 1454 m (1). Bahamas: USNM E19288 , Columbus Iselin 60, Tongue of the Ocean, 24º26’06”N, 77º29’W, 28 Feb 1973, 2793– 2825 (1); USNM E19295 , Columbus Iselin 103, Tongue of the Ocean, 24º08’N, 77º22’W, 21 Sep 1973, 1450 m (1); USNM E19294 , Columbus Iselin 301, no data (1). Caribbean Sea: USNM 16893, Albatross 2117, Aves I., 15º24’40”N, 63º31’30”W, 27 Jan 1884, 1249 m (1); USNM E42680 , JSL-II 1729, off Speightstown, Barbados, 13º15’30”N, 59º45’47”W, 16 Apr 1989, 866 m (1); USNM E17842 , Pillsbury 847, NW of Tobago, 11º37’18”N, 59º24’W, 2 Jul 1969, 733– 1281 m (1); MCZ 231, Albatross 2751, St. Kitts and Nevis, 16.9ºN, 63.2ºW, 28 Nov 1887, 1257 m (1). Brazil: MCZ 232, Albatross 2756, Fortaleza, 03.367ºS, 37.817ºW, 14 Dec 1887, 763 m (1). NHM 88.11.9.1, Challenger 122, off Barra Grande, 09º05’S, 34º50’W, 10 Sep 1873, 640 m (1).

Diagnosis. A species of Atelecrinus in which the centrodorsal usually tapers from the base; fulcral tubercles moderately to strongly developed; basals inflated interradially, forming continuations of usually well-developed ridges on centrodorsal; angle of radial profiles usually>90º; Iax2 hexagonal with weakly- to well-developed lateral knob- or ear-like lobes, or short diverging lateral margins; exterior margin of IIbr1 and IIbr2 and usually interior margin of IIbr3+4 flattened, often with a thick ridge along the edge.

Redescription of the holotype. Centrodorsal conical, tapering from its base; basal diameter 2.3 mm; HD 1.15; interradial ridges strong. Cirri XXXV, with an immature peripheral socket apparently beginning a third column in two radial areas; tubercles prominent. Basals swollen interradially. Radial profile>90º. IBr2 almost smooth in profile with weak synarthrial swelling. Ibr1 with distolateral corners slightly swollen. Iax2 hexagonal with lateral margins diverging distally or with weak lateral thickening. IIbr1 and IIbr2 somewhat thickened and expanded exteriorly; well separated. IIbr3+4 1.4 mm across.

Description of other specimens. Centrodorsal conical and tapering from its base (Figures 6a, c, d) or rarely with slightly swollen sides (Figure 6b); aboral tip conical or blunt; basal diameter 2.1–3.9 mm; HD 1.0–1.4; interradial ridges usually well developed, ranging from short (Figure 6a) to half height of centrodorsal (Figures 6b, c), rarely extending almost to tip; fulcral tubercles moderately to strongly developed; sockets in 2 columns per radial area of 2–5 sockets each; small apical sockets sometimes present.

Cirri XX– XLII (chiefly XXV–XXX); one complete apical cirrus of 30 cirrals (Figure 6e), 30 mm long, laterally compressed and tapering to a straight conical terminal segment; c1–2 short; c3 slightly longer than wide; following cirrals increasing in length to c7 with LW 3.0; cirrals beyond c9 decreasing in length but remaining with LW at least 2.0; no opposing spine. Proximal 10 segments of a peripheral cirrus consisting of c1–3 short; c4 squarish; following increasing in length; c9 with LW 4.0.

Externally visible portion of basals usually inflated interradially, sometimes with the center knob-like rather than triangular (Figure 6c); ends ranging from extremely thin to almost as high as interradial knob; rarely not visible midradially (Figure 6d). Radials shallow U-shaped with diverging lateral margins, WL 2.0–3.6; thin margins of muscular fossae sometimes visible between adjacent Ibr1; radial profile usually>90º.

IBr2 with weak to strong synarthrial swelling. Ibr1 oblong with shallow to moderately deep V-shaped distal margin, WL 1.2–2.4; weakly- to well-developed small distolateral triangular or rounded projection usually present on more than one ossicle (absent in small specimen). Iax2 hexagonal with weakly- to well-developed lateral knob- or ear-like lobes (Figure 6a) or short parallel or diverging lateral margins (Figure 6c); WL 1.0–1.4. Exterior margin of IIbr1–2 weakly to strongly flattened, often with a thickened ridge (Figure 6c), and with weak to moderate synarthrial swelling. IIbr1 longer exteriorly, distal margin shallow V-shaped; WL 1.5–2.3; interior margin almost as long as exterior, and distal margin almost straight in smaller specimens. IIbr2 irregularly quadrate; WL 1.2–1.5. IIbr3+4 often flattened interiorly, 1.3–2.7 mm across. IIbr5 almost triangular. USNM E19295 with one ray missing; pair of probolus Adidas TM facing each other on axils on either side of missing ray (one short or broken), suggesting that the missing ray had a probolus Adidas TM facing outward on each axil. Both Thor specimens have the typical two processes facing each other on adjacent axils. One specimen ( E17879 ) with one undivided ray.

USNM E42680 , the smallest known but most complete specimen, differs chiefly in having less well developed diagnostic features and proportionally more elongated ray ossicles. Centrodorsal with strong interradial ridges extending almost half way to tip, and with a few remaining apical sockets; HD 1.2; basal diameter 1.9 mm. Cirri XXIII, with 1–3 per column. Radials with WL 1.9. IBr2 lacking synarthrial swellings; Ibr1 squarish, with slightly concave sides, weak distolateral triangles, and distal margin very shallowly V-shaped; WL 1.3. Iax2 distinctly hexagonal with slightly diverging lateral margins, slightly projecting laterally on two as incipient lobes; WL 1.1. IIbr1–2 slightly flattened exteriorly. IIbr1 slightly longer exteriorly, with distal margin shallowly concave; WL 1.5. IIbr2 irregularly quadrate; WL 1.2. IIbr3+4 1.1 mm across. IIbr5 wedge-shaped; WL 1.4. IIbr8 almost oblong; WL 1.0. Brachials following IIbr9+10 weakly wedge-shaped and slightly longer than wide, with slightly raised distal margins. Syzygial interval 3–4. P1 on IIbr16–17 (on IIbr15 on an arm with IIbr10+11 instead of IIbr9+10). All pinnules broken; first pinnular short; second trapezoidal, narrower distally and longer than wide (LW 1.3); following segments longer and slenderer, up to at least LW 7.0 and with somewhat expanded distal ends.

Distribution. North and west of the British Isles, Gulf of Mexico, southern Blake Plateau, Strait of Florida, Bahamas, eastern Caribbean Sea and Brazil. Bathymetric range: 640–1450 (possibly 1454) m, with one Bahamian record from 2793–2825 m. Atelecrinus helgae appears to occur in deeper water than At. balanoides wherever the two co-occur (maximum possible ranges given): 1061–1400 vs. 512–781 m in the Gulf of Mexico; 1003–1454 vs. 514–733 m in the Strait of Florida; 1450–2825 vs. 658–714 m in the Bahamas, and 866–1257 vs. 598–838 m in the Lesser Antilles. (USNM E17842 was collected somewhere between 733–1281 m off Tobago.) At. helgae also generally occurs at shallower depths at higher latitudes. Records from the Blake Plateau (805–897 m), NE Atlantic (698–900 m) and Brazil (640–763 m) are shallower than those for the Gulf of Mexico, Bahamas and Caribbean Sea (chiefly 1003–1454 m with one record off Barbados in 866 m), though this must also reflect varying oceanographic conditions: the Gulf of Mexico records are deeper than those from the Blake Plateau at similar latitudes.

Remarks. AH Clark (1913) distinguished the holotype of At. helgae from At. balanoides by its smaller, straight-sided (i.e., not parallel-sided at the base) and more sharply conical centrodorsal with more numerous and crowded cirrus sockets. Clark and Clark (1967) added the Thor specimen and diagnosed At. helgae only by its smaller size and sharply conical centrodorsal just slightly longer than the basal width, although they also noted that the lateral edge of the axil may bear a prominent tubercle. Both specimens were collected in the NE Atlantic, while At. balanoides was restricted to the tropical W Atlantic. AM Clark (1970), in comparing the Challenger specimen of At. balanoides from Brazil with the Thor specimen, found no significant differences between their centrodorsals and synonymized At. helgae under At. balanoides . Messing and Dearborn (1990) treated At. helgae as a deeperwater infrasubspecific variant of At. balanoides (form helgae ) based mostly on material collected in the Strait of Florida and Caribbean Sea by the University of Miami’s R/V Gerda and Pillsbury (though they gave no station data). These specimens share with NE Atlantic At. helgae the centrodorsal tapering from the base with more prominent interradial ridges, fulcral tubercles and basal swelling; radial profiles>90°, and thickened or flattened exterior margins of IIbr1 and IIbr2 and (sometimes) interior margin of IIbr3+4. The ridge- or knob-like lateral margins of the hexagonal axils are more prominent in most of the W Atlantic specimens than in the holotype. They noted that the helgae form was collected chiefly below 1000 m but that most of the distinctions between it and typical At. balanoides were “not uniformly clear-cut relative to depth” ( Messing and Dearborn 1990: 23). However, reexamination of existing specimens plus new material suggests that, although some character overlap exists, At. helgae constitutes a valid species distinct from At. balanoides . In specimens with a weakly developed lateral ridge or knob on only one or two axils (e.g., the holotype, USNM E19290 and E19285 ), the other axils remain hexagonal (with diverging lateral margins) and differ from the rhombic form typical of At. balanoides . Axils are similarly hexagonal in the few specimens that lack any lateral ridge or knob, including both the Thor specimens from the NE Atlantic and Challenger specimen from Brazil. It is thus not surprising that AM Clark (1970) considered them the same species. The Challenger specimen is here treated as At. helgae , although its identity remains uncertain. A few other specimens with some other less well developed diagnostic features still appear distinguishable from At. balanoides , e.g., USNM E17842 has short, weak interradial ridges but retains a radial profile angle>90°, very short radials, and IIbr1 with the exterior margin thickened.

Atelecrinus helgae appears to be less abundant than At. balanoides on substrates amenable to trawling and dredging. Whereas more than a third of the trawl samples of At. balanoides recorded here included three or more specimens (up to 25), no more than two At. helgae specimens were ever taken in a single haul.

Although AH Clark (1913) and Clark and Clark (1967) indicated that the Thor collected a single specimen, the jar contains two specimens with the same station data. Both are partly dissociated. The holotype of At. helgae is almost completely dissociated.