Ptilocrinus (Ptilocrinus) clarki Roux & Lambert, 2011, n. sp.
Creators: name: Roux, Michel
name: Lambert, Philip
Publisher: name: Zenodo
Year: 2011
Subjects: Biodiversity
Taxonomy
Animalia
Echinodermata
Crinoidea
Hyocrinida
Hyocrinidae
Ptilocrinus
Ptilocrinus clarki

description: Ptilocrinus (Ptilocrinus) clarki n. sp.
Etymology. This species is dedicated to Austin H. Clark in memory of his eminent contribution to our knowledge of crinoids.
Material examined. 58 specimens and isolated fragments of stalk and arms from five stations off British Columbia (Table 1). The specimen n°29 from station 004-00055-007 is designated as the holotype with the catalogue number RBCM 010-00065-001.
Diagnosis. Relatively large species, usually with proximalmost stalk diameter (Dp) more than 3.0 mm and 30 pinnules or more per arm side (up to 45). Aboral cup conical or bowl-shaped (usually Hc/Dc 0.85+0.1 and Dc/Drb 1.7+0.25). Radials smooth or with small, weak transverse ridges in lower half; upper interradial edge bent inward toward oral/aboral axis just above transverse rib. Lower part of basal ring subcylindrical, forming a prolongation of proximal stalk. Tegmen inflated up to Br9, Br 11 in larger specimens; Wr/Wb frequently greater than 1.75; fifty or more thin irregular polygonal tegminal plates in each inter-ray. Proximal arm pattern 1+2 3 4 5+6 7+8 (about 50%) or 7 8+9 (about 25%) with first pinnule on Br4 (90%) or Br5 (10%); up to 4 successive brachial pairs in proximal arm, usually 2 to 6 successive free brachials in mid arm. Adoral face of proximal arm frequently inflated, with numerous small lateral plates and flattened projections on one side of brachial and first pinnular, especially in large specimens. Proximal part of pinnules asymmetric, with polygonal lateral plates not in rows, more numerous on one side and progressively disappearing distally. Stalk symplexies normally with 7 crenular units (rarely 8 or 9, 6 in early ontogeny) of 1–2 crenulae in juveniles to 3–4 crenulae in large specimens; areola without ligamentary pit; syzygial crenularium labyrinthic in distal mesistele to regularly multiradiate with 20–24 long radial crenulae in dististele; H/D of columnals never more than 0.6 except in young specimens (Dp<3.0), usually less than 0.5.
FIGURE 11. Ptilocrinus clarki n. sp., holotype. a: D–E inter-ray; b: C–D (anal) inter-ray.
Description. Measurements of the main characters and arm patterns observed in the crown are presented in Tables 6 to 13, respectively.
HOLOTYPE: Largest specimen of the type series with proximal stalk and crown, relatively robust arms (Wr/Wb 1.9), dense pinnulation, and a large interradial space occupied by an inflated tegmen (Figs. 11–12). Longest part of arm attached to theca 55.7 mm, bearing 13 pinnules on each side; maximum pinnule length 27 mm. Br1–3 developing small lateral wings; Br2 and Br3 as wide as Br1; arm axis progressively narrower distally (Br1 width 5.7 mm, decreasing to 4.0 mm in Br30); free brachials or brachial pairs not constricted midway between two muscular articulations; muscular articulations oblique after Br4–5 (Fig. 12). First pinnule always at right on Br4; proximal arm pattern 1+2 3 4 5+6 7+8 (2 cases) or 8+9 (2 cases), 1+2 3 4 5 6 7+8 (1 case); beyond Br9, brachial pairs at 12+13 (2 cases), 10+11, 11+12, 13+14, 15+16, 17+18, 23+24, 26+27, 32+33 (1 case each); series of more than 4 successive muscular articulations predominating in middle arm; one arm with series of 12 successive muscular articulations after Br14. Maximum length of pinnules 27 mm (Fig. 13a). Genital pinnules not clearly differentiated; proximal part moderately inflated with polygonal lateral plates never in rows and more numerous on right side (Fig. 13b); proximalmost inflation due to enlargement of cover plates (Fig. 13c); lateral plates disappearing progressively toward middle of pinnule (Fig. 13d); cover plates usually subrectangular, relatively thick and in a regular assemblage of alternating small and larger plates (frequently grouped in pairs) allowing a close protection of the ambulacral groove.
FIGURE 12. Ptilocrinus clarki n. sp., proximal arms and B–C inter-ray of the holotype.
Tegmen (Fig. 14) flexible without any ornamentation, strongly but regularly inflated with proximal pinnules remaining free; top at level of Br11; height 21.8 mm. About 50 or more thin flat irregularly polygonal plates per interradius; plates of the upper tegmen smaller than below and with numerous quite inconspicuous hydropores. Orals smooth and convex forming a flat peristomal ring; each oral at top of interradial angle formed by rectangular cover plates in regular rows (Fig. 14b). Anal sac relatively inconspicuous adjacent to the oral cone, slightly higher than oral ring. Aboral cup bowl-shaped; basals fused, forming a cylindrical prolongation of proximal stalk in lower part, and abruptly widening in upper part (Fig. 15a); small short ridges perpendicular to sutures between adjacent radials and between radials and basal ring (Fig.15b); coarse ribs prolonging arm axes less developed (Figs. 11 and 15a); upper radial edge curved inward underlying aboral cup – tegmen boundary. Height of aboral cup 16.7 mm; height of radial ring 10.5 mm; diameter of cylindrical base of basal ring 5.2 mm; diameter at base of radial ring 12.4 mm; diameter at top of radial ring 21.1 mm; ratio of upper radial to primibrachial (Br1) width 1.88.
FIGURE 13. Ptilocrinus clarki n. sp., proximal architecture of genital pinnule in the holotype (SEM micrographs). a: general lateral view; b: adoral view beyond genital inflation; c: lateral view of genital inflation (location on a); d: lateral view of the other side (distal end of genital inflation at left); cv: cover plates; lpa: lateral plates belonging to the side of view a; lpd: lateral plates belonging to the side of view d; lpd’: erected lateral plates decreasing from left to right; Pn: pinnular (aboral ossicle).
Length of preserved stalk attached to aboral cup 28 mm; proximalmost diameter 5.1 mm, decreasing to 3.7 mm at the distal end of preserved stalk; section heptagonal. Proximal symplexies with 7 large crenular units of 4 to 5 crenulae, well-developed perilumen and 7 long narrow areolar zones reaching outer facet border (Fig. 16a).
PARATYPES: In paratypes, proximal stalk usually cylindrical, rarely with heptagonal section as in the holotype. Complementary information on stalk, especially on its articulations, on arms and tegmen is given for a few selected paratypes, followed by a study of character variations using all the specimens.
Stalk of specimen 55-07-12: Stalk with fragments of aboral cup, distal part missing; length 207 mm; proximalmost diameter 4.0 mm, decreasing to 3.4 mm with maximum height 1.4 mm (relative thickness H/D 0.41) at a distance of 58 mm from basal ring; columnal diameter increasing to 3.5 mm (H/D 0.37) at distal end of preserved stalk. Proximal symplexies resembling those of holotype but with 8 crenular units of 4–5 crenulae (Figs. 16b, c); near minimum stalk diameter, main part of facet covered by symplexial crenularium with 8 crenular units of 3 crenulae; more distally, areolar lobes restricted to mid inner part of facet and development of syzygial crenularium beginning near its outer border (Fig. 16d).
FIGURE 14. Ptilocrinus clarki n. sp., tegmen of the holotype. a: general view with arm of ray E removed; b: enlargement of top (location on a); a: anus, cv: cover plates, m: mouth at center of flat oral ring.
FIGURE 15. Ptilocrinus clarki n. sp., aboral cup of the holotype. a: general view; b: enlargement of plate sutures showing small transverse ridges; R: radial, B: basal ring, arrow indicates cylindrical base of basal ring.
FIGURE 16. Ptilocrinus clarki n. sp., columnal symplexies of large specimens (SEM micrographs). a to c: proximalmost columnals; d–e: transition between symplexies and syzygies in distal mesistele; a: holotype; b to d: paratype 55-7-12 (distance of 207 mm between c and d); e: paratype 55-7-3 (at a distance of 191 mm from distal attachment disk); cl: claustrum.
Stalk of specimen 55-07-03: Mid and distal isolated stalk; length 191 mm; distal end broken near attachment disk; proximal diameter 3.0 mm increasing progressively to 4.3 mm at distal end; relative thickness (H/D) of columnals 0.37 in proximal part decreasing distally to 0.25. Proximal articulations corresponding to middle stalk with juvenile symplexial pattern in center with 7 crenular units of 2–3 crenulae and narrow zone of syzygial labyrinthic crenularium just inside smooth facet margin (Fig. 16e); at a distance of 92 mm from distal end, syzygy with well developed labyrinthic crenularium and juvenile symplexy more restricted to facet center with 7 crenular units of 1–2 crenulae and pentagonal lumen (Figs. 17a, c); distal syzygies typical with crenularium of 20–24 regularly radial labyrinthic crenulae derived from early juvenile pattern of 6 or 7 crenular units (Figs. 17b, d).
FIGURE 17. Ptilocrinus clarki n. sp., columnal syzygies of the paratype 55-7-3 (SEM micrographs). a and c: columnal in distal mesistele with labyrinthic crenularium; c: symplexial pattern of early ontogeny of the columnal; b and d: distalmost columnal just before attachment disk with multiradiate crenularium; d: facet center without trace of juvenile symplexy; distance of 70 mm between a and b.
Stalk of small specimens: In smallest specimen 71-16-2, stalk length 161 mm, distal stalk missing; proximalmost diameter 1.6 mm, minimum diameter 1.3 mm with height 1.4 mm (relative thickness 1,1) at a distance of 42 mm from aboral cup; diameter increasing to 1.9 mm (relative thickness 0.76) at distal end; symplexies near Dm with 7 crenular units of 1–2 relatively short crenulae near facet border and large concave areola predominating on facet with larger meshes identifying perilumen and separating areolar lobes of smaller meshes (Fig. 18a); distal articulations (Fig. 18c) with outer facet covered by irregular patchy syzygial crenularium and juvenile symplexial pattern in center as observed near Dm. In specimen 72-06, preserved stalk length 79 mm; Dp 2.2 mm; Dm 1.5 mm at a distance of 10 mm from aboral cup increasing to 1.7 mm at distal end; maximum columnal height 1.1 (H/D 0.64) at distal end with functional symplexies having 7 crenular units of 2 crenulae and conspicuous perilumen (Fig. 18b), resembling Dm symplexies of specimen 71-16-2 but with crenularium more developed and only areolar lobes slightly depressed. In specimen 71-16-1, preserved stalk length 106 mm; Dp 3.1 mm; Dm 2.4 mm and height 1.44 mm (H/D 0.6) at a distance of 21 mm from aboral cup; distal columnal with diameter 2.6 mm and height 1.38 (H/D 0.53); distal articulations with symplexial pattern predominating, with 9 crenular units of 2–3 crenulae and narrow marginal zone of syzygial crenularium (Fig. 18d).
FIGURE 18. Ptilocrinus clarki n. sp., Columnal articulations in young specimens (SEM micrographs). a–b: mesistele symplexy in paratype 72-6 (at a distance of 79 mm from aboral cup); c: distal syzygy in the smallest paratype 71-16-2 (at a distance of 161 mm from aboral cup); d: transition from symplexy to syzygy at a distance of 106 mm from aboral cup in paratype 71-16- 1.
FIGURE 19. Ptilocrinus clarki n. sp., tegmen in paratypes. a: smallest paratype 71-16-2 with relatively large oral cone (C-ray arm removed, arrow indicates mouth, cv: proximalmost cover plates); b: broken tegmen of large paratype 55-7-46 showing isolated anal sac.
Longest preserved stalks: Smallest specimen 55-07-06 has the longest preserved stalk, length 313 mm; Dp 2.8; Dm 2.3 at a distance of 53 mm from aboral cup; distal diameter 4.1 mm. In specimen 55-07-21, length 300 mm; Dp 3.5 mm; Dm 2.9 mm at a distance of 21 mm from aboral cup; distal diameter 3.3 mm. In specimen 55-07-24, length 275 mm; Dp 4.2 mm; Dm 3.2 mm at distal end. In specimen 55-07-25, length 270 mm, Dp 3.5 mm; Dm 3.0 mm up to a distance of 81 mm from aboral cup. All the other stalks attached to aboral cups are shorter than 255 mm.
Theca and arms: Tegmen of juvenile specimen 71-16-02 moderately inflated with 16–18 tegminal plates per interray, height 5.8 mm, top at level of Br6; orals forming a conspicuous cone (Fig. 19a); anal cone as high as oral cone or slightly lower. In young specimen 71-16-01, tegmen more inflated, reaching level of Br7–8, height 12.2 mm; about 50 tegminal plates in anal (C–D) interray and 30–40 in other interrays. Basal usually fused; seven specimens (20%) with 1 to 3 sutures. Badly broken crown of large specimen 55-07-46 allows the best view of anal sac at top of C–D interradius coalesced with corresponding oral (Fig. 19b); one arm is almost complete, 125 mm long, with about 40–45 pinnules on each side, maximum pinnule length 28–32 mm, observed in mid arm. In young specimen 71-16-01, longest preserved arm 65 mm with about 25 pinnules on each arm side, maximum pinnule length 32 mm, observed in mid arm.
Pinnule architecture: Proximal part of pinnules of variable length (to ~ 15 mm) with numerous lateral plates on one side allowing asymmetrical collapse of adoral structure (Figs. 20a to c); other side mainly with relatively long cover plates (Fig. 20d); lateral plates and zigzag suture of cover plates disappearing in mid pinnule; large elongated and rounded cover plates becoming thinner distally and oriented transversely (Fig. 20e). In smallest (possibly immature) paratypes, proximalmost part of pinnules with just a few relatively inconspicuous lateral plates on one side and large cover plates on the other side; rectangular cover plates in two regular rows covering food groove in arm and proximal part of pinnule (Figs. 21a,b). In larger specimens, arm with adoral pavement of irregular polygonal cover and lateral plates (Fig. 21c); adoral face of proximal arm inflated and appearing with a typical aspect between pinnule bases (Fig. 21d). Brachial synostoses flat; muscular synarthry of brachial bearing pinnule with open adoral groove and with fulcral ridges of pinnule socket and brachial facet parallel (Fig. 22a); pinnule socket with deep ligament and muscle fossae (Fig. 22b). First pinnular articulated on brachial by transverse synarthry of prominent fulcral ridge (Fig. 22c); first and second pinnulars articulated by wide classical muscular synarthry (Fig. 22d); these two articulations allowing a large amplitude of flexibility in two perpendicular orientations; the following articulations are flat synostoses uniting asymmetrical pinnulars in a relatively rigid segment (Figs. 22e, f); distal part of pinnule with muscular synarthies (Fig. 22g), which allow the pinnule to roll up.
FIGURE 20. Ptilocrinus clarki n. sp., pinnule architecture in paratype 4-68-10 (SEM micrographs). a–b: distal part of genital inflation; b: zigzag suture of cover plates; c: cross section through a; d: lateral view of middle part of pinnule; e: cover plate arrangement in distal part; cv: cover plates, lp: collapsed pavement of lateral plates, Pn: pinnular (aboral ossicle).
Variation in main quantitative morphological characters: Measurements on ~ 30 specimens from the type locality (55-07) provided significant information on intra-population variation; eight basic quantitative characters were measured and combined into seven ratios (Tables 6–7). The wide range of sizes (shown by the growth index of 2.5<Dp<5.2) provided variation rates above 10% in basic variables and higher than 14.5% for Dp, Dm, Hr and Drb (Table 6). All ratios in Table 7 have variation rates lower than 10%, except 11.3% for Drb/Dp; the lowest rate is 5.8% for Hc/Dc. Table 8 shows the range of variation in basic variables among specimens of a size that corresponds to the mean Dp value of 3.5 mm. After integration of specimens from other sites, including several juveniles (Table 9), intraspecific variations of ratios appear relatively independent of growth and without a clear ontogenetic trend. Fig. 23 shows the wide variation in main external morphological traits of the theca from small to large specimens. Station 68-10 had too few specimens to permit comparison of possible variations relative to environment with those from station 55-7.
Variation in arm pattern: About 90% of preserved arms have the first pinnule (P1) on Br4 and 10% on Br5 (Table 10). Proximalmost arm pattern usually 1+2 3 4 5+6 (74 %). Articulation Br1–2 muscular in 5 arms of specimen 55-7-41 and in 1 or 2 arms of 4 other specimens; Br2+ 3 in a single arm and Br3+ 4 in 4 arms. Pattern 1+2 3 4+5 most frequent (8 cases) when P1 on Br5 (14 arms), specimen from site 69-8 having four arms with this pattern and one with P1 on Br4. Beyond Br6, pattern more variable (Tables 10 and 11); brachial pairs more frequent proximally and series of successive muscular articulations distally (Fig. 24). Distally, more than 20% of brachial pairs at 32+33 and 39+40. Number of successive brachial pairs rarely 4, more frequently 3 (15%) usually before Br12.
Beyond brachial bearing P1, series of more than 3 successive free brachials beginning before Br20 (78%), mainly between Br11 and Br16 (45%) with number usually fewer than 8, exceptionally up to 14 or 18, never more than 25 in distal arm (Table 11). Wide range of arm pattern variation appearing both in individual crowns and among specimens collected. Specimens 55-7-31 and 68-10-4 each bearing one arm with only 4 brachial pairs for 33 and 38 brachials, respectively (76% and 79% of free brachials, respectively). Opposite extreme patterns observed in another arm of specimen 55-7-31 with 6 brachial pairs for 20 brachials, and in one arm of specimen 55-7-30 with 10 brachial pairs for 33 brachials (40% and 60% of free brachials, respectively).
FIGURE 21. Ptilocrinus clarki n. sp., adoral architecture at junction of arm-pinnule (SEM micrographs). a: arm axis of immature small paratype 71-16-2; b: development of large cover plates (arrow) at pinnule base in young paratype 72-6; c–d: arm pinnule junction in large paratype 68-10; c: pinnule in open position; d: pinnules in closed position; acv: arm cover plates; pcv: pinnule cover plates; ps: pinnule socket (pinnule removed); Br: brachial (aboral ossicle); P: pinnule; Pn: pinnular (aboral ossicle).
TABLE 6. Values of main quantitative characters of stalk and aboral cup among specimens of Pticocrinus clarki n. sp. from site 55-07. Dc: upper diameter of aboral cup, Dm: minimum stalk diameter, Dp: proximalmost stalk diameter, Drb: aboral cup diameter at basal/radial suture, Hc: aboral cup height, Hr: radial height, Wb: primibrachial width, Wr: upper radial width. Values in mm.
Characters Wb Wr Dc Drb Hc Hr Dp Dm Minimum value 3.9 5.9 11.1 6.2 10.2 5.9 2.6 2.0 Maximum value 5.9 10.7 21.1 13.0 17.8 10.7 5.1 3.4 Mean value 5.04 8.74 17.07 10.15 14.62 8.26 3.60 2.76 Standard deviation 0.53 1.14 2. 0 9 1.56 1. 37 1.20 0.53 0.42 Variation rate % 10.52 13.04 12.24 15.37 9.37 14.53 14.72 15.22 Number of measures 29 29 29 29 26 29 39 30
TABLE 7. Values of main morphological ratios of stalk and aboral cup among specimens of Ptilocrinus clarki n. sp. from site 55-07. Abbreviations as in Table 6.
FIGURE 22. Ptilocrinus clarki n. sp., brachial and pinnular articulations in paratype 68-10 (SEM micrographs). a–b: free brachial; a: proximal facet (muscular synarthry); b: adoral view showing oblique nature of articulation and large pinnule socket; c: transverse muscular synarthry of proximalmost pinnular (articulation Pn1-Br); d: proximal facet of Pn2 (muscular synarthry); e: distal view of Pn2 with synostosial facet; f: flat synostosis of Pn8; g: distal pinnular with muscular synarthry.
TABLE 8. Values of main quantitative characters of stalk and aboral cup at the same growth stage in specimens of Ptilocrinus clarki n. sp. from the site 55-07. For ratios, see Table 9. Abbreviations as in Table 6. Dp and Dm are used as index of growth (in yellow). Nsp: specimen numbers.
TABLE 9. Values of main quantitative characters (ratios) through growth of stalk and aboral cup among the type series of Ptilocrinus clarki n. sp. using specimens from the five stations. Dp (column at right) is used as index of growth. Abbreviations as in Table 6. Colours distinguish different stations.
Specimen Hc/Dc Wr/Wb Hr/Hc Hr/Wr Drb/Dp Dc/Drb Dp/Dm Dp continued next page
Specimen Hc/Dc Wr/Wb Hr/Hc Hr/Wr Drb/Dp Dc/Drb Dp/Dm Dp 55-7-17 0.89 1.81 0.65 0.98 3.00 1.48 1.41 4.1 55-7-33 0.85 1.75 0.59 0.99 2.71 1.76>1.28 4.1 55-7-38 0.91 1.96 0.54 0.95 2.74 1.57 1.45 4.2 55-7-24 0.92 1.69 0.58 0.98 2.38 1.57 1.31 4.2 55-7-30 0.82 1.78 0.57 0.93 2.64 1.70>1.31 4.2 55-7-29 0.79 1.88 0.62 0.98 2.43 1.70>1.38 5.1 FIGURE 23. Ptilocrinus clarki n. sp., variation in theca of young paratypes. a: paratype 71-16-2 (Dp = 1.6 mm); b: paratype 72-6 (Dp = 2.2 mm); c: paratype 55-7-43 (Dp = 3.0 mm); d: paratype 71-16-1 (Dp = 3.1 mm); e: paratype 69-8 (Dp = 3.2 mm); f: paratype 55-7-40 (Dp = 3.4 mm).
Specimens from site 68-10 display significant differences in arm pattern relative to those from other stations (Tables 10, 12 and 13, Fig. 25) with a higher frequency of muscular articulations, especially from Br9 to Br16, and locations of brachial pairs less variable (frequency>20% at 7+8, 11+12, 17+18, 25+26, and 34+35). Smallest specimen from this site (68-10-4, Dp 3.0 mm) with long series of successive muscular articulations (up to 12) following Br 6 in four arms, and following Br 9 in the fifth with the exceptional number of more than 20 in the second series following Br18. Among young specimens (Dp <3.4), frequency of free brachials before Br16 73% at site 68-10 and usually (90% of arms) 33–47% at other sites with one case each of 20% and 60%.
Gastropod parasitism: Specimens 72-6, 55-7-17 and 55-7-36 were parasited by a gastropod, presumably Eulima ptilocrinicola Bartsch, 1907, as described in a few paratypes of Ptilocrinus pinnatus. Tegmen or proximal arms with typical gastropod beveled holes (Figs. 26a to c); holes on brachial pair located on synostosis. Smaller perforations on imbricating cover plates of proximal pinnule (Fig. 26d) probably due to the same predator.
TABLE 10. Frequency of main patterns in proximal arm between Br4 and Br10 among the type series of P. clarki n. sp. with a comparison between the two main sites. Yellow background: frequency of Br4 bearing P1. Arm pattern as in Table 11.
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
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
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 32-39 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
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
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 17+18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33-38 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
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 2728 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 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
continued 1+2 3 4 5+6 7 8+9 10+11 12+13 14 15 16 17 18 19 20 21+22
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 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
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 33-38 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 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 32-36 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
FIGURE 24. Ptilocrinus clarki n. sp., global distribution of free brachial and brachial pairs frequencies along arms in the studied population.
FIGURE 25. Ptilocrinus clarki n. sp., differences in distribution of free brachial and brachial pairs frequencies along arms at stations 55-7 (red curves) and 68-10 (green curves).
FIGURE 26. Ptilocrinus clarki n. sp., gastropod predation on tegmen and proximal arm (SEM micrographs). a: paratype 71- 16-1; b–d: paratype 72-6; a: beveled hole (arrow) on tegmen; b–c: beveled hole (arrow) on lateral face of a brachial pair at the level of synostosial suture (s); d: small holes (arrows) on genital inflation in proximal pinnule.
Remarks. Arm pattern and morphological characters vary widely in P. clarki n. sp., at scales of species, population and individual. However, using data from a significant number of observations, it appears that the following characters can be diagnostic: first pinnule on Br4 (90%), proximal arm pattern 1+2 4+5 7+8 or 8+9 (75%, the first one predominating with ~50%), usually fewer than 7 successive free brachials in mid arm, and three quantitative characters of aboral cup (Hc/Dc, Dc/Drb, Wr/Wb) that vary at a rate nearly equal to or less than 8%.
P. clarki n. sp. provides important information on cover plate ontogeny. In other hyocrinids and most extant stalked crinoids, cover plates are usually strongly differentiated, frequently in a gathered arrangement from orals to pinnule bases, or at least on the tegmen between arms and orals. In P. clarki n. sp., flat rectangular plates form two regular rows covering the food groove from orals to pinnule bases (Fig. 21); on the tegmen, two rows (each from adjacent rays) form an angle with one oral at top (Fig. 14). The orals clearly appear as the first cover plates, forming a flat roof over the mouth. Cover plates on the pinnules are differentiated in a sequence. Proximally, they occur in an alternating pattern of large and small plates, a small plate corresponding to a large one in the adjacent row (Fig. 13). Distally, the large plates are more rounded and oriented transversely (Fig. 20d), with the small plates frequently becoming quite inconspicuous.
In juveniles, additional lateral plates are absent in arms and pinnules (Fig. 21a) except for a few rudimentary plates on one side of the pinnule base. In adults, especially in large specimens, they become well developed, forming a pavement of polygonal adoral plates in the arm (Fig. 21c), and allowing proximal genital inflation of the pinnule (Fig. 13). The distal part of a pinnule is the youngest skeleton to appear during ontogeny of the crown; thus, cover plates complete their differentiation later in P. clarki n. sp. than in other hyocrinid genera or subgenera.
During columnal ontogeny, maximum height is quickly attained in the proximal mesistele. Its value remains about the same (from 1.1 to 1.4 mm) in the distal stalk and in large specimens. Change in relative thickness (H/D) through ontogeny is mainly due to growth in diameter distally. The maximum value of H/D in a given stalk (0.7 to 1.1) characterizes the youngest specimens. In specimens with a proximalmost diameter larger than 3 mm, it is never more than 0.6.
The number of crenular units in symplexies varies from 7 to 9 (usually 7) independent of columnal diameter, while the number of crenulae per crenular unit and length of crenular units increase with proximal stalk diameter. In functional symplexies, the perilumen with galleried stereom of large meshes is surrounded by a depressed areola. The depression is more marked between crenular units but is always slight, never deep (Fig. 18a). Columnals grow mainly in height in the mesistele. Distally, columnals only grow in diameter, and a flat perifacet with syzygial crenularium develops around the symplexy.
The distal stalk displays two ontogenetic profiles of columnals. The first develops a multiradiate syzygial crenularium in the distal stalk of juveniles; it is located in the distalmost stalk of adults, and the early juvenile symplexial pattern is usually inconspicuous (Figs. 17b, d). The second develops later in stalk ontogeny from a mesistele symplexy with a syzygial crenularium of patchy or labyrinthic pattern (Fig. 18c), sometimes tending to a concentric labyrinthic pattern (Fig. 17a) as described in the Feracrinus stalk (Mironov & Sorokina 1998a – b; Améziane & Roux 2011); it appears in the distal mesistele of adults, and the symplexial juvenile pattern always remains conspicuous in the facet center (Fig. 17c).
Before discussing what characters differentiate P. c l a r ki n. sp. and the type species of the genus, P. pinnatus, additional information on this latter species is presented below.
Occurrence. Northeastern Pacific off British Columbia, depth: 1,178 to 1,986 m, possibly 1,164 to 2,105 m.
description: Published as part of Roux, Michel & Lambert, Philip, 2011, Two new species of stalked crinoids from the northeastern Pacific in the genera Gephyrocrinus and Ptilocrinus (Echinodermata, Crinoidea, Hyocrinidae). Effects of ontogeny and variability on hyocrinid taxonomy, pp. 1-54 in Zootaxa 2825 on pages 18-36, DOI: 10.5281/zenodo.277262