Hyocrinus bethellianus, Eléaume, Marc, Bohn, Jens-Michael, Roux, Michel & Améziane, Nadia, 2012

Eléaume, Marc, Bohn, Jens-Michael, Roux, Michel & Améziane, Nadia, 2012, Stalked crinoids (Echinodermata) collected by the R / V Polarstern and Meteor in the south Atlantic and in Antarctica, Zootaxa 3425, pp. 1-22 : 12-15

Hyocrinus bethellianus Thomson, 1876

Figures 7–8; Table 4 .

Synonymy: Hyocrinus bethellianus Thomson, 1876: 51 –54, figs 2–5; Carpenter, 1884: 218–224, pl. V (figs 4–10), pl. VI; Doderlein, 1912: 5–9, figs 1–2, pl. I (figs 1–5), pl. II (figs 1–6), pl. IX (fig. 1); Clark, 1915: 162–163; Rasmussen, 1978: T828, fig. 556-4; Roux, 1980b: 34, 36, 42–46, pl. II (figs 1–2); Mironov & Sorokina, 1998b: 31; H. bethellianus bethellianus Mironov & Sorokina, 1998b: 31 ; H. bethellianus subsp. n. Mironov & Sorokina, 1998b: 31–33, fig. 9, pl. 5 ( Figs 1–4 ), pl. 10 ( Fig. 5 ); H. bethellianus Roux & Pawson, 1999: 294 ; Roux et al., 2002: 821; Roux & Lambert, 2011: 46, 48, 51, figs 33–34; Hess, 2011b: T173, fig. 85 (1a–b).

Material examined. R/V Polarstern cruise ANDEEP III/PS 67/142-6, 62°10’32”S, 48°29’41”W to 62°9’43”S, 48°30’43”W, depth 3403–3405 m (1 large specimen ZSM 20043128). Walvis I/ CP01, 33°53’6”S, 05°07’2”E to 33°53’6”S, 05°06’7”E, 5037–5040 m, 1978, (1 juvenile specimen, MNHN IE- 2012-756).

Description. Specimen ZSM 20043128: Complete specimen except distal end of stalk (Fig. 7A). Tegmen not inflated, with a pyramidal oral cone of large concave orals (Fig. 7B–C); 15–20 tegminal plates of variable size and number per interray; C–D interray with small globular anal sac and oral with a conspicuous tubercule in center (Fig. 7B); food grooves with cover plates in a gathered arrangement forming a bridge between orals and Br6; tegmen height 4.5 mm at top of oral cone. Aboral cup slightly higher than broad, height 10.9 mm, upper radial diameter 9.9 mm; diameter at radial/basal sutures 8.1 mm, radial height 6.4 mm, radial width 6.3 mm; primibrachial width 1.5 mm, ratio of radial to primibrachial width 4.14. Inter-rays very wide and arms gracile (Fig. 7A). Maximum arm length about 80.0 mm; up to 11 pinnules per arm side; maximum pinnule length 16.5 mm, proximalmost arm pattern always 1+2 3+4 5+6 with the first pinnule on Br6 at left; usually (97%) brachial triplets (a+b+c) distally except two cases of brachial pair (a+b) on the same arm. Genital inflation in six or seven proximal pinnules of each arm, due to one row of H-shaped plates becoming irregular and smaller proximally with an additional row of lateral plates (Fig. 7D); cover plates regularly rounded with a radial ornamentation of small stereom meshes near the outer border (Fig. 7E). Length of proximal stalk attached to aboral cup 49.4 mm; proximalmost diameter 1.96 mm, distally decreasing to 1.65 mm at a distance of 3.4 mm from basal ring, to 1.55 mm at a distance of 6.4 mm and up to 1.35 mm at distal broken end. Proximal columnal articulated by symplexies with 8 crenular units of 1–2 crenulae, areola of large stereom meshes and a large axial canal (ratio of lumen to columnal diameter 0.4) with a conspicuous claustrum (Fig. 7F–G); distalmost preserved columnals about as high as broad articulated by symplexies with smaller axial canal (ratio of lumen to columnal diameter 0.2) and predominating radial crenularium (Fig. 7H).

7. Hyocrinus bethellianus (ZSM 20043128). A: proximal arms and theca, view of anal (C–D) interray; B: enlargement of A, showing tegmen with large oral cone (oc) and small anal cone (an); C: tegmen in A–B interray; D: proximal inflation of genital pinnule (p: pinnular, hp: H-shaped plates, cv: cover plates); E: detail of cover plates; F–G: proximal columnal; H: distal columnal of the preserved stalk.

Specimen MNHN IE-2012-756: Small juvenile ( Fig. 8 A). Arms broken at Br6 (length 6.2 mm), proximal pattern 1+2 3+4 5+6 with base of first pinnule on Br6; proximal pinnulars as wide as brachials; proximal arm cover plates rounded ( Fig. 8 B), resembling those on pinnules of ZSM 20043128 and becoming diamond-shaped distally. Tegmen restricted to oral cone ( Fig. 8 C); orals concave with hydropores at base, oral height 1.6 mm, diameter at tegmen base 3.1 mm, anal cone inconspicuous. Aboral cup broken. Length of preserved proximal stalk attached to broken basal ring 3.9 mm, proximalmost diameter 0.48 mm, diameter at broken end 0.39 mm.

Remarks. The holotype ( Carpenter, 1884) and the Vityaz specimen ( Mironov & Sorokina, 1998b) are relatively small. The specimen ZSM 20043128 is significantly larger. However, it is slightly smaller than the Tiefsee specimen ( Döderlein, 1912). These four specimens share the main characters of the species despite the wide variations in their aboral cups. The mesistele symplexies of the holotype have 6 or 7 crenular units of 1 small crenula restricted to the facet border ( Roux, 1980b), which correspond to an early stage of columnal ontogeny. The ZSM specimen displays the derived characters (greater number of tegminal plates, well developed crenularium with 8 crenular units of up to 2 crenulae), which appear throughout ontogeny in larger specimens. The small juvenile from Walvis Ridge undoubtedly belongs to H. bethellianus because of its typical cover plates. The Vityaz specimen from the North Pacific documents a wider species distribution in the Indo-Pacific province than previously expected.

Occurrence. North Pacific, Antarctic slope off Enderby Land, W of Crozet Island and SW of Walvis Ridge, at depths of 2926 to 5037 m, possibly 2915 to 5040 m.

specimens.

Synonymy: « Hyocrinus proche de H. (Gephyrocrinus) grimaldii » Roux, 1980b: 903 .

Material examined. Walvis I cruise, station DS01, 33°53’9 S–05°05’9 E to 33°53’9 S–05°06’4 E, 5205–5240 m, 1978 (1 juvenile, MNHN IE- 2012-755).

Description. Complete specimen except distal stalk ( Fig. 9 A). Length of preserved stalk 5.1 mm, proximalmost diameter 0.7 mm, diameter at end of preserved stalk 0.5 mm. Aboral cup conical with basal fused, cup height 2.4 mm, upper radial diameter 3.3 mm, diameter at basal/radial suture 1.9 mm, lower basal ring diameter 0.9 mm, radial height 1.4 mm. Tegmen with small anal cone and moderately large orals ( Fig. 9 B); orals concave with a median knob in their lower part, tegmen height 1.1 mm. Arm length 12.8 mm, proximal arm pattern 1+2 3+4 5+6 with first pinnule on Br6; arm as wide as pinnule; cover plates triangular with sharp top ( Fig. 9 C).

Remarks. This juvenile specimen undoubtedly belongs to the genus Hyocrinus and to a different species than H. bethellianus based on its tegmen and cover plates. Cover plates with similarly sharp triangular ends have been described in Hyocrinus cyanae Bourseau et al., 1991 ( Roux 2004, Fig. 7b) collected off New Caledonia at a depth of 2536 m, suggesting that this specimen could belong to this latter species. Confirmation of its identity with new material, would give Hyocrinus cyanae a wide Indo-Pacific distribution similar to that of H. bethellianus .

Figures

FIGURE 1. Stalk articulation in Bathycrinus aldrichianus (USNM E 17896). A – B: proximal synarthries, C: mid mesistele synarthry, D – E: distal mesistele synarthries, F: dististele synarthry, A: small juvenile, B – D: medium-sized specimen, E – F: large specimen.

FIGURE 2. Bathycrinus australis (ZSM 20020004). A – G, I – J: large specimen; H, K – L: juvenile specimen; A – B: views of crown; C: distal stalk with bases of thin roots; D: progressive transition from dististele to mesistele; E: other distal stalk with large roots encrusting pebble; F – H: distal synarthries; I – L: mesistele synarthries.

FIGURE 3. Dumetocrinus aff. antarcticus. A – E: specimen PS 69 / 710 - 5; F: holotype of Dumetocrinus antarcticus (IRSNB 1897 / 1999 - 10131 - 589); D: symplexy of proximal mesistele; E – F: syzygies in distalmost stalk; an: anal sac; oc: oral cone.

FIGURE 4. Holotype of Feracrinus heinzelleri n. sp. (ZSM 0000 / 1). A: general view with ray broken at Br 2 / 3; B: anal sac in CD interray; C: oral cone, view from broken A ray; D: lateral view of pinnule insertion on arm; E: hyposynostosial brachial showing flat synostosial facet; F: episynostosial brachial, distal facet showing pinnule socket (arrow head) and interbrachial muscular synarthry (arrow); G: lateral view of same brachial (side of pinnule insertion). Star: muscular articulation.

FIGURE 5. Holotype of Feracrinus heinzelleri n. sp. (ZSM 0000 / 1), pinnule ossicles. A – C: views of the two proximalmost pinnulars (p 1 and p 2); A: proximal adoral view showing facet of muscular transverse synarthry; B: adoral view, proximal transverse synarthry at right, distal synostosis at left, p 1 articulated to p 2 by muscular synarthry (see D); C: distal adoral view showing flat synostosial facet; D: proximal synarthry of p 2; E: pinnular in mid pinnule with synostosial facets; F: distal pinnular with muscular articulations; G – I: H-shaped genital plate; G: front view; H: lateral external view, ambulacral side at top; I: lateral internal view; J: profile view of genital, H-shaped and covering plates on genital pinnule; K: detailed view of covering plates; L-M: dissociated proximal cover plate. adp: additional lateral plates; cp: cover plates; gp: genital H-shaped plates; p: pinnular.

FIGURE 8. Juvenile of Hyocrinus bethellianus (MNHN IE- 2012 - 756) from Walvis Ridge. A: oral cone with two proximal arms; B: lateral view of arm with cover plates; C: detail of orals with three hydropores at base of right oral (arrow).

FIGURE 9. Juvenile of Hyocrinus sp. (MNHN IE- 2012 - 755) from Walvis Ridge. A: general view; B: tegmen with oral cone (oc) and anal cone (ac), one arm removed; C: lateral view of arm with sharp cover plates.

Tables

TABLE 4. Sampling stations of the five specimens of Hyocrinus bethellianus Thomson, 1876 currently known. N: number of

Cruise/Station	Location	Depth (m)	N	References
Challenger Exped.,/47	46°16’ S–48°27’ E	2926	1	Carpenter, 1884
Tiefsee Exped./152	63°16’ S–57°51’ E	4636	1	Döderlein, 1912
Vityaz, 1955/ 3364	48°21.2’ N–168°54.1’ E	2915–3015	1	Mironov & Sorokina, 1998b
Walvis I/ CP01	33°53’6 S–05°07’2 E to 33°53’6 S–05°06’7 E	5037–5040	1	juvenile this paper
ANDEEP III/PS 67/142-6	62°10’32”S–48°29’41”W to 62°9’43”S–48°30’43”W	3403–3405	1	this paper
Hyocrinus sp. Figure 9.