Figures 9–16, Tables 9–15.
Synonymy: Ptilocrinus brucei Vaney in Wilton, 1908: fig. 70, pl. 23; Vaney & John, 1939: 661 –664, 1 pl.; A.H. Clark, 1915: 161; Smaldon et al., 1976: 74; Roux, 1980 b: 36, 41, 53, pl. 3 (figs. 5–6); Roux et al., 2002: 822. P. (Chambersaecrinus) brucei: Mironov & Sorokina, 1998: 52 –55, fig. 19–20, pl. 8 (figs. 4–5); Roux & Lambert, 2011: 45, 48, 51; Eléaume et al., 2014: 210–211.
P. (Chambersaecrinus) flexibilis Mironov & Sorokina, 1998: 55 –57, fig. 21, pl. 11 (fig. 2).
Holotype. NMS 1921.143. 1743, S. Y. Scotia, sta. 301, NW Weddell Sea, 64 ° 48 ’S – 44 ° 26 ’W, depth 4,585 m (2,485 fms).
Material examined. NHM 1939.5. 13.1 (paratype), S. Y. Scotia, trawl 3426, off South Orcade Islands, 62 ° 10 ’S, 41 ° 20 ’ W, depth 3,245 m (includes note by D. John in 1938: specimen was “broken into small species but among them some individual plates, radials, etc.. are recognizable”.); USNM 1005433, South East Pacific basin, 63 ° 0.3 ’to 63 °12.0’S – 128 ° 12 ’ to 128 ° 11 ’W, depth 4,682 m (2 specimens; 1 with theca, proximal arm and stalk; 1 juvenile with complete stalk, basal ring and fragments of proximal arms and radials); USNM 1005438, South Atlantic Ocean, Scotia Sea, South Georgia Island, 54 °00’– 54 °05’S, 33 ° 40 ’– 33 ° 43 ’W, depth 2663–2718 m (1, partly fragmented, theca poorly preserved, fragments of proximal arms with radials); USNM 1005439, South Atlantic, Scotia Sea, NE of South Shetland Islands, 59 °S– 51.9 °W, depth 3,010–3,510 m (1 theca, proximal arms and stalk fragments); USNM 1105453 -A South Orkney Islands, Scotia Ridge, 62 °09’ à 62 ° 16 ’S – 38 ° 11 ’ à 38 ° 24 ’W, depth 3,056–3,459 m (dissociated radials, basal ring, proximal brachials and proximalmost columnals).
Emended diagnosis. A species of Ptilocrinus (Chambersaecrinus) reaching large size; proximalmost stalk diameter to 4.5 mm, arm length to 130 mm with about 40 pinnules on each side, and pinnule length to 55 mm. External morphology variable; ratio of cup height to adoral diameter 0.97–1.36; ratio of cup to radial height 1.01– 1.65 (usually 1.20–1.34); ratio of radial to first brachial width 1.45–1.97; ratio of adoral cup to proximalmost stalk diameter 3.25 (small specimen) to 4.27 (usually 3.97–4.20); arm deeply inserted on adoral radial edge; basal cup and proximalmost stalk diameter usually equal; maximum ratio of columnal height to diameter in a given stalk from 1.43 in smallest specimen to 0.41 in large specimens. Tegmen inflated and rounded; anal cone significantly taller than oral cone and reaching level of Br 8 to Br 14 in large specimens; base of anal cone peripheral on tegmen; upper part of cone oriented toward tegmen center; orals smooth and concave with rounded top; as many as 20 large polygonal tegminal plates sometimes with a regular median arrangement. Arm pattern variable, from chiefly alternating free brachial and brachial pairs to long series (more than 20) of successive free brachials beyond the third brachial pair; proximalmost arm pattern 1 + 2 3 4 5 + 6 7 (75.9 %), 1 + 2 3 4 5 + 6 7 + 8 (13.8 %); first pinnule usually on Br 4 (94.7 %), rarely on Br 5; most frequent brachial pairs beyond Br 7 at 8 + 9 (44.0%), 10 + 11 (22.7 %) and 18 + 19 (27.3 %). Brachial muscular synarthry with conspicuous process prolonging adoral groove. Pinnule inserted on distal adoral side of brachial; proximal part with asymmetrical genital inflation; great number of additional small proximal plates decreasing distally; additional plates imbricated or irregularly aligned.
Stalk symplexies with 6 (young stage) to 14 (usually 8–12) crenular units of 1 crenula of various lengths; up to 3 crenulae or subsidiary crenulae developed between units in large specimens; axial canal in proximal mesistele enlarges substantially during ontogeny; lumen bordered by coarsely-meshed galleried stereom; distal syzygies with thin irregular radial crenularium.
Description. Tables 9 and 10 list biometric parameters, including holotype and paratype. The small number of specimens and the wide range of character variations preclude obtaining robust results from statistical analyses on the main changes in quantitative ratios during ontogeny.
USNM 1005439: Theca well preserved with proximal and mid arms (Fig. 9 A–B) strikingly resembling the original figure of the holotype (Wilton 1908; Vaney & John 1939). Tegmen inflated and rounded; high anal cone reaching level of Br 14, significantly taller than oral cone; base of anal cone peripheral on tegmen; upper portion of cone oriented toward tegmen center (Fig. 9 A–B); orals subvertical, smooth and concave with rounded tip; as many as 20 large polygonal tegminal plates without peculiar median arrangement in inter-rays (Fig. 9 B); inter-rays A–B, C–D, A–E wider than the two other inter-rays; hydropores on adoral quarter of tegmen; conspicuous ambulacral “bridges” between Br 10–11 and top of oral cone with cover plates in a gathered arrangement; outer ramifications of “bridges” corresponding to proximal pinnules not attached to tegmen.
Proximal arm pattern 1 + 2 3 4 5 + 6 7 (5 cases) with first pinnule on Br 4; brachial pair at 8 + 9 (3 cases) and 9 + 10 (1); number of successive muscular synarthries beyond the last brachial pair and before broken end: 6 (2 cases), 8 (1), 24 (1), and 16 including Br 7 (1). Two ossicles of a brachial pair united by flat synostosis. Pinnule socket in distal half of brachial adorally (Fig. 10 A–B); transverse muscular synarthry uniting pinnule to arm with marked fulcral ridge and deep muscular fossa on brachial (Fig. 10 E–F); free brachial with strongly oblique muscular articulations (Fig. 10 B); muscular synarthries with ambulacral groove forming a conspicuous adoral process in mid-articulation (Fig. 10 C–D). Adoral proximal arm inflated with numerous lateral plates not aligned, and conspicuous festooned cover plates in a gathered arrangement; proximal part of pinnules with proximal genital inflation of asymmetric, multiplated architecture, and cover plates poorly differentiated (Fig. 11 A–B); 3 (maximum 4) irregular plate rows on convex side decreasing to 1 row distally (Fig. 11 B); concave side without rows; lateral plates small or disappearing in mid arm with cover plates rounded or elliptical; muscular synarthries of first pinnular with brachial (Fig. 10 E) and with second pinnular (Fig. 11 E) having perpendicular fulcral ridge allowing wide amplitude of movements; symmetrical synostosis between second and third pinnular (Fig. 11 F–G); following pinnulars asymmetrical, supporting genital inflation (Fig. 11 H–I); pinnulars becoming more symmetrical distally.
Length of proximal stalk attached to aboral cup 5.0 mm with 10 columnals; proximalmost diameter 3.4 mm; cup aboral diameter 3.4 mm; stalk distal diameter 3.0 mm. Stalk fragment with distal proxistele and transition to mesistele: length 17.05 mm with 22 columnals; proximal diameter 2.95 mm with maximum columnal height 0.9 mm, and symplexy with 11 crenular units of 2–3 crenulae (fig. 12 B–C); distal diameter 2.8 mm with maximum columnal height 1.6 mm and symplexy with 11 crenular units of 1 robust crenula (Fig. 12 D); inner areola and probably claustrum depressed proximally (diameter 1.3 mm), with round lacuna of diameter 0.5 mm; inner areola surrounded by coarsely-meshed stereom; stereom of depressed area progressively resorbed distally, resulting in a larger axial canal (diameter 1.0 mm) (Fig. 12 B–D); ratio of axial canal to columnal diameter in this fragment from 0.44 (proximal) to 0.36 (distal).
USNM 1005438: Large specimen in fragments, lacking aboral cup: radials attached to arms, fragment of inflated tegmen and tall anal tube, and complete stalk except proximalmost columnals. Proximal arm pattern 1 + 2 3 4 5 + 6 7 8 with first pinnule on Br 4 (5 cases), brachial pair at 9 + 10 (1), 10 + 11 (2), and no other brachial pair (1); fifth arm broken after Br 8; mid arm with free brachial only; maximum number of muscular articulations before broken end 21; distal arm fragments rarely with one brachial pair; muscular articulations oblique beyond Br 4; Br 1 to Br 3 with lateral wings. Height and width of brachials moderately decreasing from Br 1 to Br 3 and very little beyond Br 3 (Table 11). Arms attached to tegmen to Br 9; adoral face of arm inflated and multiplated, with festooned cover plates in a gathered arrangement; genital inflation of some pinnules with numerous imbricated irregular polygonal plates not in rows (Fig. 11 C), covering exceptionally preserved gonads with oocytes of 100– 150 µ (Fig. 11 D); other pinnules with asymmetric architecture described above; arm and pinnule articulations as in previous specimen.
Remaining stalk length 386 mm (five fragments without gap); Table 12 lists quantitative columnal parameters; columnal diameter increasing rapidly at distal end suggesting stalk broken close to attachment disk. Proximalmost columnal with 14 crenular units (poorly preserved); number of crenular units decreasing to 12 of one crenula in proximal mesistele (Fig. 13 A), to 11 with numerous subsidiary crenulae in mid mesistele (Fig. 13 B), and to multiradiate symplexy with initially 10 crenular units observed at center in distal mesistele (Fig. 13 C); transition symplexy/syzygy (Fig. 13 D) with development of syzygial stereom on facet surface (Fig. 13 E) indicating short dististele (30–40 mm) with anchylosed articulations; distalmost columnals with facet entirely covered by syzygial stereom, juvenile symplexial pattern of 6 small crenular units of 1 crenula and pentalobate lumen at center (Fig. 13 F). Axial lumen diameter to 1.8 mm proximally; ratio of lumen to columnal facet diameter 0.45 in proxistele and proximal mesistele, decreasing slowly to 0.25 in distal mesistele and rapidly to 0.09 in dististele. From distal proxistele to mid mesistele, axial canal surrounded by galleried stereom of large meshes bordering small deep ligamentary pits fused with lumen and alternating with crenular units (Fig. 13 G–H and J–K); pit floor corresponding to depressed inner areola (see below specimen 1005433 B, Fig. 14 D); this character disappearing in distal mesistele (Fig. 13 I and L) and dististele.
USNM 1005433 -A: Aboral cup tall; radials more than three times taller than broad (Fig. 9 C). Tegmen inflated to Br 4 or more proximally; about 10 tegminal plates per inter-radius; ambulacral “bridges” between Br 8 and mouth with festooned cover plates in a gathered arrangement; oral cone shorter than anal cone; orals smooth and slightly concave; top of oral cone flat. Pattern of proximal arms attached to theca 1 + 2 3 4 5 + 6 7 (2 cases) and 1 + 2 3 4 5 + 6 7 8 + 9 10 (3) with first pinnule on Br 4; brachial pair following Br 10 either 11 + 12 (1 case) or 15 + 16 (1). Radial and proximalmost brachial articulations as in USNM 1005453 (see description below).
Length of preserved stalk 23.0 mm; proximalmost diameter 2.8 mm, decreasing to 2.4 (ratio of columnal height to diameter 0.42) at distal broken end; proximalmost symplexies with 9 crenular units of 1–2 crenulae (Fig. 14 A–C); ratio of claustrum to columnal diameter up to 0.54; tallest columnals (first order in growth sequence) showing formation of a large axial canal with perilumen underlined by large stereom meshes (Fig. 14 A).
USNM 1005433 -B: Juvenile specimen of proximal stalk diameter 1.9 mm, 89.5 mm long, allowing observation of a young stage of stalk ontogeny along stalk length. Table 13 lists quantitative morphological parameters. Columnal slightly barrel-shaped (Fig. 14 F) having maximum height in mid stalk with ratio of height to diameter up to 1.43. Symplexies with 8 crenular units of 1 short crenula (Fig. 14 D–E); inner areola more depressed proximally than distally; ratio of depressed areola to facet diameter 0.46–0.54; axial canal perilumen marked by conspicuous large stereom meshes; claustrum in proximal columnal with pentalobate to multilobate lumen; thin multiradiate syzygial crenularium developing in distal mesistele (Fig. 14 E–F).
USNM 1005453: Badly preserved specimen; all ossicles dissociated; all remaining ossicles similar to those of other specimens. Proximalmost arm pattern 1 + 2 3 4 with first pinnule on Br 4. Radial with deep arm insertion (Fig. 15 A); inner surface with two sub-parallel conspicuous nervous canals (Fig. 15 A–B); synarthry joining radial and Br 1 with well differentiated inner (adoral) ligament and muscular areas (Fig. 15 C), this differentiation becoming less conspicuous in the following muscular synarthries (Fig. 15 E and G); Br 3 with deep adoral groove (Fig. 15 G); synostoses flat; stereom of synostosis 1 + 2 with small meshes only on Br 1 facet (Fig. 15 D) and small meshes aborally plus larger ones around lumen and adorally on Br 2 adjacent facet (Fig. 15 F). Only proximalmost columnals remaining; articulations with 14 crenular units of 1 crenula with various lengths and pentalobate lumen (Fig. 12 A); no stereom differentiation between claustrum and inner areola.
HOLOTYPE AND PARATYPE: Quantitative parameters of the holotype and paratype listed by Vaney (in Vaney & John 1939) were usually overestimates. Mironov and Sorokina (1998) re-examined the large holotype (NMS 1921.143.1743), which is now in poor condition. I used Vaney & John’s (1939) measurements for calibrating measurements of the large and fine original photograph of the holotype when it was still well-preserved (Vaney 1908) (Tables 9 and 10). General holotype morphology is as in USNM 1005439 (Fig. 9 A). Each arm was about 110–130 mm long with the distal ends rolled up, about 40 pinnules on each side; maximum pinnule length 55 mm with 40 pinnulars. Proximal arm pattern 1 + 2 3 4 5 + 6 7 with first brachial on Br 4 (4 cases); one arm described by Vaney with the following brachial pairs at 9 +10, 16+ 17 24 +25, 33+34, 40+ 41; other arms with brachial pairs at 8 + 9 (2 cases), 13 +14, 14+15, 17+18, 18+ 19 (1 case each). Stalk length about 530 mm; proximalmost diameter 3.5 mm, decreasing to 3.0 at a distance of 15 mm from cup; maximum ratio of columnal height to diameter 0.71 in mid stalk.
The paratype (NHM 1939.5.13.1) is fragmented. However, proximal arm pattern reconstruction is possible: 1 + 2 3 4 5 + 6 7 + 8 9 10 + 11 12 (3 cases), 1 + 2 3 4 5 + 6 7 8 + 9 10 11 12 + 13 (1), 1 + 2 3 4 5 6 7 8 + 9 10 11 + 12 (1); usually free brachials alternating with brachial pairs distally. Five radials preserved. Stalk very fragmented; total length of all fragments about 90 mm; proxistele lost; proximalmost diameter inferred from other stalk fragments about 2.5 mm (3.0 mm after Vaney); minimum values in proximal mesistele: columnal diameter 1.95 mm, columnal height 1.45 mm, ratio of height to diameter 0.86; maximum values in mid and distal mesistele: columnal diameter 2.2 mm, columnal height 2.5 mm, ratio of height to diameter 1.43; maximum values in distalmost fragments: columnal diameter 2.7 mm, columnal height 1.5 mm, ratio of height to diameter 0.56. Symplexies with 10–11 crenular units of 1 crenula in proximalmost fragments and coarsely-meshed stereom in inner areola and perilumen (Fig. 16 A); 8– 9 crenular units of 1 crenula in mid mesistele; 7 crenular units of 1 short crenula in juvenile pattern at facet center in distal mesistele (Fig. 16 B). Transition between mesistele and dististele with multiradiate crenularium of up to about 20 wide crenulae (Fig. 16 B and D); distalmost syzygies examined with numerous thinner radial crenulae becoming irregular in outer facet (Fig. 16 C and E).
Remarks. Mironov & Sorokina (1998) described two other poorly preserved specimens collected off the Orkney Islands by Russian cruises. The specimen attributed to P. brucei was collected at R/V Dmitri Mendeleev sta. 4094, 60° 42.8 ’– 43.1 ’S to 41 °03.0–01.9’W, depth 4,070–4,570 m. Proximal arm patterns included two variants: 1 + 2 3 4 5 + 6 with first pinnule on Br 4 (3 cases) and with one of these arms with the third brachial pair at 8 + 9 followed by 6 successive muscular articulations, and 1 + 2 3 4 + 5 with first pinnule on Br 5 (2 cases) and with one of these arms with the third brachial pair at 7 + 8, number of successive muscular articulations 5–15 in mid arm fragment and 2–3 in distal arm. Anal cone height about 11.1 mm. Three stalk fragments with total length 163.2 mm (Table 14); estimated proximalmost diameter about 2.7 mm; symplexies with 9–10 crenular units of 1–2 crenulae; ratio of lumen to columnal diameter 0.25 in mid stalk. The second specimen, attributed to a new species P. flexibilis Mironov & Sorokina, 1998, was collected at R/V Akademic Kurchatov sta. 908, 60° 13.5 ’– 12.9 ’S to 44 ° 10.6 ’– 12.2 ’W, depth 5,465–5,474 m (Moscow State Univ. Zoological Museum cat. no. C- 20). Proximal arm patterns 1 + 2 3 4 5 + 6 7 8 (1 case) and 1 + 2 3 4 5 + 6 7 + 8 (1). Roux & Lambert (2011) considered P. brucei and P. flexibilis as conspecific.
The current study documents the wide range of intraspecific variation in P. (C.) brucei. Fig. 9 illustrates the range in variation in external morphology. Arm pattern varies from chiefly alternating free brachials and brachial pairs to long series of successive muscular articulations beyond the third brachial pair (Table 15); proximalmost arm pattern 1 + 2 3 4 5 + 6 7 (75.9 %), 1 + 2 3 4 5 + 6 7 + 8 (13.8 %); first pinnule on Br 4 (94.7 %); brachial pair at 8 + 9 (44.0%), 9 + 10 (13.0%), 10 + 11 (22.7 %), 13 + 14 (15.0%), 15 + 16 (18.7 %), 18 + 19 (27.3 %), and other brachial pairs <13 %. The adoral process in brachial muscular synarthries has never been described in the other species of Ptilocrinus. Genital pinnules display an asymmetrical architecture. Exceptionally preserved submature oocytes> 100 µm across (Fig. 11 C–D) suggest that larvae could be lecithotrophic. The number of crenular units in stalk symplexies increases throughout ontogeny from 6 to 12 (possibly 14), but the rate of this change varies from an individual to another; usually each crenular unit has 1 crenula of various lengths, but sometime up to 3 crenulae or with subsidiary crenulae between units in the largest specimens. The enlargement of the axial canal in the proximal mesistele through ontogeny is also variable. Small specimens have relatively tall columnals (maximum ratio of columnal height to diameter 1.43) compared to the largest specimens (0.41). The anal cone is always significantly higher than the oral cone. The arrangement of interadial tegminal plates into a median row is irregular and frequently absent. As pointed out by Roux & Lambert (2011), this character cannot be used to identify subgenus Chambersaecrinus.
Ptilocrinus (C.) brucei shares with P. (Ptilocrinus) clarki Roux & Lambert, 2011, an asymmetrical architecture in the proximal part of the genital pinnules, and, with P. (P.) amezianeae Eléaume et al., 2011, and Dumetocrinus antarcticus Bather, 1908, significant enlargement of the axial canal through ontogeny, more than 10 crenular units in symplexies of large specimens, and frequently long series of free brachials in mid arm. Roux & Lambert (2011) placed P. brucei and P. stukalinae within subgenus Chambersaecrinus. P. stukalinae mainly differs in having a less inflated tegmen, cover plates with a long terminal projection, symplexies with 6–8 crenular units of 1–3 crenulae, ligamentary pits between crenular units, and without enlargement of the stalk axial canal through ontogeny.
Occurrence. Southern Ocean from 33 ° to 128 °W and from 54 ° to 63 °S (NW Weddell Sea; South Georgia, Orcade, Orkney and Shetland Islands; SE Pacific basin), depth 2,718 to 5,465 m (possibly 2,663 to 5,474 m).
1 + 2 3 4 5 6 7 8 + 9 10 11 + 12 13 14 15 + 16 17 18 + 19 20 21 + 22 23 24 + 25 26 27 + 28 29 30 + 31 ** 1 + 2 3 4 5 + 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
1 + 2 3 4 5 + 6 7 8 9 10 + 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1 + 2 3 4 5 + 6 7 8 9 + 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 1 + 2 3 4 5 + 6 7 8 9 + 10 11 12 13 14 15 16 + 17 18 19 20 21 22 23 24 + 25 26 27 28 29 30 31 32 33 + 34 * 1 + 2 3 4 5 + 6 7 8 + 9 10 11 12 13 14 15 16
1 + 2 3 4 5 + 6 7 8 + 9 10 11 12 13 14 15 + 16 17 18 19
1 + 2 3 4 5 + 6 7 8 + 9 10 11 12 13 14 + 15 16 17 18 + 19 20 *
1 + 2 3 4 5 + 6 7 8 + 9 10 11 12 13 + 14 15 16 17 + 18 19 *
1 + 2 3 4 5 + 6 7 8 + 9 10 11 12 + 13 14 15 + 16 17 18 + 19 20 21 + 22 23 24 + 25 26 27 + 28 29 ** 1 + 2 3 4 5 + 6 7 8 + 9 10 11 + 12 13 14 15 16
1 + 2 3 4 5 + 6 7 + 8 9 10 + 11 12 13 14 + 15 16 **
1 + 2 3 4 5 + 6 7 + 8 9 10 + 11 12 13 + 14 15 16 + 17 18 19 + 20 21 **
1 + 2 3 4 + 5 6 7 + 8