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 Author Roux, Michel Author Lambert, Philip text Zootaxa 2011 2825 1 54 journal article 10.5281/zenodo.277262 b9c2d7e0-8764-499d-bb41-12d19355479c 1175-5326 277262 Gephyrocrinus messingi n. sp. Etymology. This species is kindly dedicated to Charles Garrett Messing of Nova Southeastern University (Florida) who provided the specimens collected during MBARI cruises. Material examined. The specimen trawled in October 2006 off Cape Scott (Vancouver Island), Queen Charlotte Sound, is designated as the holotype , catalogue number RBCM 007-00004-011. Four other specimens were collected during MBARI cruises off California using the ROV “Tiburon”: (1) two specimens in October 2003 on the basaltic rocky substrate of Rodriguez Seamount, registration numbers in SIO E4426; (2) two others in 2004 on hard ground of San Juan slope, registration numbers in SIO E4427. Table 1 gives detailed locations of specimens. Diagnosis. A species of the genus Gephyrocrinus with a normal proximal arm pattern of 1+2 3 4 5+6 7+8 9+10 (80%) and first pinnule on Br4; beyond Br4, free brachials more frequently at Br13 (52%), Br16 (64%) and Br19 (64%); three or more successive muscular articulations appearing rarely after Br15, more frequently after Br19; pattern very variable beyond Br25, from series of more than 15 successive muscular articulations (sometime reaching the arm tip) to exceptionally long series of successive brachial pairs. Brachial constriction between two muscular articulations more marked in juveniles than in adults. Base of genital pinnules with numerous small polygonal lateral plates not in rows; shape (frequently irregularly sub-quadrangular) and size of lateral plates variable on two sides of genital inflation, frequently present in middle pinnule at least on one side; cover plates rounded to sharply lanceolate. Tegmen with a verrucose ornamentation, variously inflated, frequently globular, relative inter-ray width (Wr/Wb) usually more than 2.0, anal sac bottle-shaped slightly shorterer or taller than oral cone, orals smooth with rounded top. Conical aboral cup with a conspicuous ornamentation of radial ribs and transverse ridges, basal fused, aboral border of basal ring flanged. Columnal symplexies with 6–7 crenular units of 1–2 short crenulae (up to 3 in largest specimens). TABLE 2. Variation of main morphological characters in the type series of Gephyrocrinus messingi n. sp. La: arm length; Lp: pinnule length; Np: number of pinnules on each arm side; Wb: Br1 width; Wr: radial width; Hc: aboral cup height; Hr: radial height; Dc: uppermost diameter of aboral cup; Drb: diameter at radial-basal sutures; Dp: proximalmost stalk diameter; Dm: minimum stalk diameter. Values in mm except for Np. Dp and Dm are used as growth index (in yellow).

Specimen	La	Lp	Np	Wb	Wr	Hc	Hr	Dc	Drb	Dp	Dm
T662-B	22	13	8	0.8–0.9	1.8	3.5	2.0	4.2	1.6	1.3	0.78
T662-A	49	21	19	1.8–1.9	4.5	7.0	3.8	6.9	4.4	2.2	<1.5
Holotype	>57	>30	>27	2.5–2.7	5.2	8.6	5.1	8.7	5.3	2.3	<1.78
T629-1	98	29–31	29–32	2.4–2.7	5.3–5.7	8.6	5.4	9.8	5.7	2.4	1.8
T629-2	104	32–42	28–30	2.6–2.9	5.9	8.7	5.5	9.8	6.3	2.7	1.86

TABLE 3. Variation of main morphological ratios through ontogeny in the type series of Gephyrocrinus messingi n. sp. Abbreviations and growth index as in Table 2. Specimen Lp/La Hc/Dc Hr/Hc Hr/Wr Wr/ Wb Dc/Drb Drb/Dp Dp/Dm T662-B 0.59 0.83 0.57 1.1 2.00–2.25 2.6 1.23 1.7 T662-A 0.43 1.01 0.54 1.2 2.37–2.50 1.6 2.0>1.5 Holotype - 0.99 0.59 0.98 1.93–2.08 1.64 2.30>1.3 T629-1 0.29–0.32 0.88 0.62 0.95–1.0 2.11–2.21 1.72 2.37 1.3 T629-2 0.31–0.40 0.89 0.63 0.93 2.03–2.27 1.56 2.33 1.45 Description. The main morphological measurements and arm patterns observed in the crown are given in Tables 2, 3 and 4, respectively. HOLOTYPE : Specimen with proximal stalk and nearly complete crown (Fig. 2). Arms moderately graceful (Wr/ Wb about 2.1), rolled up near distal end, bearing about 30 well-differentiated pinnules on each side or slightly more (maximum 27 observed before broken arm end) with a wide space between successive pinnules especially in proximal part of arms (Fig. 2). FIGURE 3. Gephyrocrinus messingi n. sp. , arm and base of pinnule. a to c: holotype ; paratype (T629-A4-2); a–b: lateral view of pinnule base; c: inflated and mutiplated adoral architecture of arm; d: same arm part without inflation; a-c-d: light microscopy; b: SEM view; fcv: festooned cover plates in a gathered arrangement, pv: pavement of polygonal lateral plates. FIGURE 4. Gephyrocrinus messingi n. sp. , brachial and pinnular ossicles of the holotype ( SEM micrographs). a: hyposynostosial brachial, proximal facet (synarthry); b to e: episynostosial brachials, b: proximal facet (flat synostosis), c: distal facet (synarthry), d: ventral-distal view, e: lateral view with pinnule socket; f: pinnular beyond genital inflation. TABLE 4. Variations of arm pattern in the type series of Gephyrocrinus messingi n. sp. ; Dp used as growth index; red numbers: free brachials; black numbers: brachial pairs; bold numbers: brachial bearing the first pinnule. San Juan I, T622-B (Dp = 1.3 mm ) 1+2 3 4 5 6+7 8+ 9 10 11 +12 13 1+2 3 4 5+6 7 8+ 9 10 11 + 12 13 14 +15 16 17 18 19 20+21 22 23 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 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 San Juan I, T622-A (Dp = 2.2 mm ) 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 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 33 34 Off Vancouver Island, Holotype (Dp = 2.3 mm ) 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 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 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 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 17 18+19 20 21 22 23+24 25 26 27 28 29 30 31 32 33 34 Rodriguez Seamount, T629-1 (Dp = 2.4 mm ) 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 3132 33+34 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 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 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 17+18 19 20+21 22 23+24 25 26 27 28+29 30 31 32 33+ Rodriguez Seamount, T629-2 (Dp = 2.7 mm ) 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 33+34 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 17+18 19 20 21 22+23 24 25 26 27 28 29+30 31 32 33 34 Tegmen easily visible interradially between narrow proximal brachials. Br2 and Br3 as wide as Br1; arm axis becoming progressively narrower distally. Free brachials and brachial pairs slightly constricted midway between their proximal and distal muscular articulations; proximal brachial with moderate lateral wings and thorns near muscular articulations. Proximal arm pattern very regular with 1+2 3 4 5+6 7+8 9+10 11+ 12 13 14 +15, and first pinnule on Br 4 in five arms ( Table 4 ); pattern of middle arm more variable; three successive muscular articulations appearing between Br16 and Br23; series of 18 or more successive muscular articulations beginning between Br25 and Br29; distal arm with a few brachial pairs irregularly placed. Maximum length of pinnules 30 mm on P2 but probably longer in middle arm. Pinnule base with polygonal lateral plates not in rows and with curved cover plates in a gathered arrangement (Fig. 3a, b); from proximal to distal part, largest lateral plates flat and irregularly rectangular on each side not united by stereom bridge; cover plates poorly preserved with variable shape, usually rounded or lanceolate, sharper distally. Adoral face of arms and proximal pinnules strongly inflated (Figs. 3a, c), the inflation decreasing distally. Brachial and pinnule articulations (Fig. 4) with the main classical features known in hyocrinids (adoral ligament area without galleried stereom, flat synostoses without stereom differentiation); adoral groove of brachials widely open between deep concave insertion area of inner ligaments and muscles (Fig. 4a, c, d); pinnule socket oblique and in relatively lateral position midway from brachial facets (Fig. 4e); pinnulars with the two lateral sides quite equal (Fig. 4f). Globular tegmen regularly inflated up to Br8, sticking to proximal arm; first pinnule remaining free. About 25 tegminal plates per interradius with verrucose ornamentation of irregular bumps or knobs (Figs. 3a, 5a). Height of tegmen at oral cone 8.4 mm . Oral cone shorter than anal sac; orals of moderate size with smooth globular top; cover plates in regular rows converging to oral cone (Fig. 5d); top of anal sac in relatively central on tegmen. Aboral cup conical, slightly bowl-shaped, strongly ornamented by conspicuous coarse ribs prolonging arm axis and subdivided in variable parallel ridges especially near basal-radial suture; 5 to 7 small perpendicular ridges on interradial surface (Fig. 6a). Basal fused; aboral border of basal ring flanged by 7 rounded knobs. Height of aboral cup 8.6 mm ; height of basal ring 3.5 mm ; diameter at base of basal ring 2.6 mm ; diameter at base of radial ring 5.3 mm ; diameter at top of radial ring 8.7 mm ; interray spaces wide (Wr/Wb 2.15 + 0.22). Length of preserved stalk 59.3 mm ; proximalmost diameter (Dp) 2.3 mm , decreasing to 1.78 mm at distal end of preserved stalk with columnal height 0.77 mm (H/D 0.43); stalk broken before minimum diameter. Proximal stalk very heterometric (thickness and diameter variable) with seven longitudinal rows of knobs aligned with knobs on base of basal ring (Fig. 6a). Proximal symplexies heptagonal with 7 short crenular units of 1 or 2 crenulae and a conspicuous claustrum (Fig. 7a), becoming circular and with 1 crenula per crenular unit in distal part of preserved stalk. PARATYPES FROM RODRIGUEZ SEAMOUNT ( SIO E4426): Two relatively large and complete specimens, distal stalk missing. Arms and pinnules gracile and flexible, rolled up at their distal end (Fig. 8). Proximal arm pattern always 1+2 3 4 5+6 7+8 and first pinnule on Br4; middle and distal arm pattern more variable than in holotype ( Table 4 ). Flat irregular lateral plates on each pinnule side (Figs. 9a, b); middle and distal parts of pinnules with smaller lateral plates at least on one side, or cover plates only; shape of cover plates usually triangular with narrow or sharp end, sometimes lanceolate and more rounded (Figs. 9b to d). H-shaped plates between the two sides absent, causing frequent collapse of adoral architecture. FIGURE 5. Gephyrocrinus messingi n. sp. , inflated tegmen. a and d: strongly inflated holotype ; b: paratype T629-A4-2; c, e and f: paratype T629-A4-1; a to c: lateral views of anal inter-ray showing conspicuous anal sac in b and c; d to e: oral cones; f: detail of oral ring. FIGURE 6. Gephyrocrinus messingi n. sp. , variation in aboral cup and proximalmost stalk. a: holotype ; b: paratype T629-A4- 1; c–d: paratype T629-A4-2. Spherical inflated tegmen; inflation not extending onto arms and pinnules. Oral cone slightly taller than anal sac; orals with rounded, smooth top and base bearing several knobs each (Figs. 5e, f). Anal sac adjacent to outer margin of tegmen, easily observed and with a group of about eight apical spines (Figs. 5b, c). Regular conical aboral cup with the same general pattern of ornamentation as in the holotype but with variable development of transverse ridges (Figs. 6b to d). FIGURE 7. Gephyrocrinus messingi n. sp. , columnal articulations of mature specimens ( SEM micrographs). a: proximal symplexy in holotype ; b–c: proximal mesistele symplexy in paratype T662-A; d-e: paratype T629-A4-1, d: middle mesistele symplexy, e–f: distal columnal of preserved stalk with development of syzygial crenularium beginning on outer facet; arrow indicates claustrum. Specimen T629-A4-1: Maximum arm length 98 mm ; two arms longer than the others; up to 32 pinnules on each arm side; maximum pinnule length 31 mm between Br26 and 30. Beyond Br4, first free brachial from Br9 to Br15, maximum number of successive muscular articulations usually 5, rarely 11 or 13 distally. Tegmen moderately inflated, not attached to proximal arm, and with a coarse vermiculate ornamentation (Fig. 5c). Top of anal sac at 7.2 mm above upper radial border; tegmen height at oral cone 8.5 mm . Diameter at base of basal ring 2.8 mm ; diameter at base of radial ring 5.7 mm ; diameter at top of radial ring 9.8 mm ; interray width (Wr/Wb) 2.16 + 0.05. Aboral cup ornamentation with a pair of coarse ribs prolonging arm axis; six small transverse ridges in each interradius and a coarse transverse rib in upper part of radial ring (Fig. 6b). Length of preserved stalk 165 mm ; proximalmost diameter (Dp) 2.4 mm , decreasing to 1.78 mm (Dm) with relative thickness (H/D) 0.45 at a distance of 41 mm from aboral cup; distal diameter 1.95 mm ; heptagonal proximal columnals becoming cylindrical distally; columnal height increasing to 1.3 mm with H/D 0.69 at 55 mm before broken stalk end; H/D 0.56 in distalmost columnal. Stalk symplexies as in the holotype with 7 crenular units of 1–2 crenulae (Fig. 7d); beginning of syzygial crenularium development at end of preserved stalk (Fig. 7e–f). Specimen T629-A4-2: Maximum arm length 104 mm , with 28 to 30 pinnules on each arm side; maximum pinnule length 42 mm between Br30 and 34. Beyond Br4, first free brachial at Br13 (4 cases) or Br15 (1 case); maximum number of 5 or 6 successive muscular articulations from Br19 to Br35; more distal pattern strongly variable from only successive brachial pairs all along distal arm (1 case) to series of more than 15 successive muscular articulations (1 case). Tegmen more inflated than in preceding specimen but less than in holotype , attached on three proximal brachials only in anal interradius (Fig. 5b); height at oral cone 8.2 mm ; height of aboral cup 8.7 mm ; radial height 5.5 mm ; diameter at base of basal ring 3.1 mm ; diameter at top of radial ring 9.8 mm ; relative interray width (Wr/Wb) 2.15 + 0.12. Two fine ridges resembling dotted lines on cup ribs prolonging arm axis; transverse ridge irregular and variable; base of basal ring moderately flanged (Figs. 6c, d). Length of preserved stalk 80 mm ; proximalmost diameter 2.7 mm , decreasing to 1.86 at a distance of 35 mm below aboral cup; distal diameter 1.89 mm with H/D 0.61; hexagonal proximal columnals with heterometry (variable thickness and diameter) less than in other specimens; stalk symplexies with 6 crenular units of 1–2 crenulae. FIGURE 8. Gephyrocrinus messingi n. sp. , theca and crown in paratypes . a and b: paratype T629-A4-2; c: paratype T629-A4- 1; a and c: theca and proximal crown; b: distal arm. PARATYPES FROM SAN JUAN ( SIO E4427): Two specimens significantly smaller than holotype , with stalk and crown. Specimen T662-A: Crown quite well preserved but with three arms separated from proximal part (two arms broken at muscular articulation 6–7, one broken at synostosis 7+8), and one broken at muscular articulation 13–14. Beyond Br4 bearing first pinnule, first free brachial at variable locations from Br11 to Br15; series more than two successive muscular articulations from Br23 with a maximum of 10. Conical aboral cup and tegmen partly crushed; aboral cup with coarse pairs of ribs prolonging arm axes and base of basal ring bearing 7 knobs aligned with series of knobs on proximal stalk; series of granules in the area of transverse ridges; moderately inflated tegmen with verrucose ornamentation; anal sac equal or slightly taller than oral cone; triangular orals well developed with concave outer surface and one finger-like projection at base. Length of preserved stalk 39 mm ; middle and distal stalk missing; proximalmost diameter 2.2 mm , decreasing to 1.56 mm at distal end; minimum diameter undoubtedly smaller than 1.5 mm . Proximal columnals heptagonal with conspicuous heterometry (diameter and thickness variable) up to 20 mm from aboral cup, becoming cylindrical distally. At distal end of preserved stalk, symplexies with 7 crenular units of 2–3 short crenulae; claustrum present; concave areolar lobes between crenular units (Figs. 7b, c). FIGURE 9. Gephyrocrinus messingi n. sp. , SEM micrographs of pinnule architecture. a: paratype T629-A4-1; b to d: paratype T629-A4-2; a: lateral view of proximal genital inflation; b: same pinnule, mid-distal part; c: well developed cover plates; d: distal end rolled up; lp: lateral plates; cv: cover plates. Specimen T662-B: Juvenile specimen quite complete, only distalmost stalk missing and two arms broken at muscular articulation 13–14 and 14–15. Beyond Br4 bearing first pinnule, first free brachial appearing at Br5 (1 case), Br7 (1 case), Br9 (2 cases) and Br11 (1 case). Series of more than two successive muscular articulations appearing from Br15 to Br18; maximum number observed 5 (1 case). Brachial constriction midway between two muscular articulations more conspicuous than in other specimens, especially in proximal arm. Same general ornamentation as in preceding specimen but less conspicuous on aboral cup, and more conspicuous and very spiny on tegmen. Tegmen not inflated; number of tegminal plates per interradius less than 12; relatively large orals with finger-like projection at top; oral cone and anal sac tops at about the same level. Stalk length 122 mm ; proximalmost diameter 1.3 mm , decreasing to 0.78 mm at a distance of 11 mm , increasing to 0.80 mm at 25 mm and up to 1.01 mm at distal end; H/D up to 0.6 distally. Mesistele symplexy (Figs. 10a to e) with 6 crenular units of 1 very short crenula, and marked areolar depression around perilumen especially at maximum columnal height (Fig. 10e). Distal syzygy with radial crenularium (Fig. 10f). Remarks and affinities. The five specimens described here belong undoubtedly to the same species and illustrate morphological variations both related and unrelated to ontogeny. They constitute a growth series from the most juvenile specimen (T662-B) to the largest (T629-A4-2). Tables 2–3 show that all the basic quantitative variables of aboral cup and stalk depend on growth, whereas ratios are independent of size (Hc/Dc, Hr/Wr, Wr/Wb, Dc/ Drb). In this case, detecting ontogenetic trends in morphological changes is difficult due to the small number of specimens. However, arms seem to grow more rapidly than pinnules, radials than basals, and size of aboral cup than stalk diameter. Variations in theca ornamentation in large specimens are illustrated in Figs. 5–6. Aboral cup ornamentation can vary in one specimen from one interradius to another as in specimen T629-A4-2 (Figs. 6c, d). The juvenile has a weak ornamentation on the theca, and its orals bear finger-like projections which disappear in the three largest specimens. This suggests changes through ontogeny. A similar pattern of aboral cup ornamentation was described in the abyssal species Hyocrinus foelli Roux & Pawson, 1999 (see also Roux 2004 , Fig. 4j). It is weakly present in the Antarctic species Dumetocrinus antarcticus (see also John 1937 , Fig. 1). So, it occurs in hyocrinid species belonging to different genera. FIGURE 10. Gephyrocrinus messingi n. sp. , columnal articulations of the juvenile paratype T622-B (SEM micrographs). a to c: symplexies in proximal mesistele; a–b: same columnal; c: opposite facet; d–e: symplexy in middle mesistele near Dm; f: syzygy of distalmost columnal; arrow indicates claustrum. Variations in arm pattern ( Table 4 ) suggest that the number of successive brachial pairs proximally and of successive muscular articulations distally tend to increase through ontogeny and can be interpreted as adaptive characters, because arm flexibility depends on frequency of muscular articulations ( Mironov & Sorokina 1998b ). Beyond Br4, the first free brachial mainly appears before Br 10 in the juvenile specimen, and after Br10 or more in larger specimens. Beyond Br25, despite muscular articulations usually predominating, the arm pattern is variable and independent of size from a series of more than 15 successive muscular articulations (sometimes reaching the arm end) to an exceptionally long series of successive brachial pairs. Except in the holotype , arm pattern can vary significantly from one arm to another in the same specimen. However, the main characters of the arm pattern are relatively constant: 1+2 3 4 5+6 7+8 9+10 (80%) and first pinnule always on Br4; beyond Br4, free brachials at Br13 (52%), Br16 (64%) and Br19 (64%); a series of three or more successive muscular articulations usually appears beyond Br19. Despite its medium size, the holotype has a more robust crown and relatively shorter arms, a very constant proximal arm pattern with four successive brachial pairs, a coarse ornamentation on the theca and the greatest inflation of the tegmen and proximal adoral face of arms. Comparing it with the other specimens, especially with the juvenile, it appears to have the most derived states of the species characters. In distal arm pattern, the most derived trend is realized in a single arm (specimen T629-A4-2) with a series of successive brachial pairs to the distal end. In the genital pinnules, variations in the extension of lateral plates and inflation of the adoral faces of arms might depend on gonad maturation. TABLE 5. Comparison of the main morphological characters in the two known species of Gephyrocrinus .

characters	Gephyrocrinus grimaldii	Gephyrocrinus messingi
Crown length	<30 mm	>40 mm
Proximal brachials	no lateral wings or spines	moderate lateral wings or spines
Arm pattern	1+2 3 4 5+6 7+8 9+10…(87%), presence of bra- chial triplets at various places, usually (99%) only series of successive brachial pairs up to arm tip, free brachials rare	1+2 3 4 5+6 7+8 9+10… (80%), brachial triplet exceptional, usually (>50%) free brachials at Br13, 16 and 19, series of successive free brachials in distal half of arms
Br bearing P1	Usually Br4 (Br5 4%)	Br4 (unknown on Br5)
IR space (Wr/Wb)	1.2 to 1.8	>1.9, usually>2.0
Pinnules/arm side	<10	>20, up to 42
Pinnule feature	Stout and relatively rigid	Graceful and relatively flexible
Pinnule socket	On distal half of brachial height	On middle part of brachial height
Lateral plates in pin- nule	Numerous polygonal plates not in rows in proxi- mal inflation, lateral plates all along pinnule	Numerous polygonal plates not in rows in proxi- malmost inflation, lateral plates all along pinnule
Cover plates in pin- nule	Rarely conspicuous in proximal and middle pin- nule, with lanceolate shape in distal pinnule	Well-developed all along pinnule, lanceolate to round
Ornamentation of theca	Absent	Very conspicuous with transverse and radial ridges
Tegmen inflation	Reaching Br4–5, to Br6–7 in largest specimens	Variously inflated, reaching Br 6–8, globular
Tegminal plates per interradius	Usually 12–15, rarely up to 18, smooth and con- vex	>20, verrucose or spiny
Anal cone	Subconical, higher than oral cone	Bottle-shaped, slightly lower or higher than oral cone
Orals	Well-developed, convex and smooth	Well-developed, frequently with rounded expan- sion at top
Aboral cup	No angle between radials and basals, no orna- mentation, base usually flanged	Angle weak or absent between radials and basals, conspicuous ornamentation, base strongly flanged
Proximal columnals	Polygonal without knobs	Polygonal with knobs

Crenular units in sym- 6–8 of 1–2 crenulae 6–7 of 1–2 crenulae (nearly 3 in largest speci- plexies men) Distal syzygies Radial to weakly labyrinthic pattern, crenulae Irregular radial pattern in juvenile, unknown in less developed adults The Atlantic species G. grimaldii differs in its small size, arms with a series of successive brachial pairs only beyond Br4, brachials lacking a constriction, relatively stout pinnules, tegmen not globular, anal sac always taller than oral cone, interray width smaller and theca ornamentation almost absent ( Roux & Bohn 2010 ) ( Table 5 ). The two species of Gephyrocrinus share the same general pattern of stalk articulations, high frequency of brachial pairs in proximal and middle arm, and pinnule architecture. Small polygonal lateral plates, which cover the genital inflation in pinnules of G. grimaldii , are restricted to its proximalmost part in G. messingi n. sp. The latter species develops larger lateral plates that allow genital inflation, but the basic elements of pinnule architecture are the same. As suggested by Roux & Bohn (2010) , and using data from G. messingi n. sp. , the arm pattern of G. grimaldii with brachial pairs reaching the arm end corresponds to the most extreme state of development of this derived adaptive character. The small size of G. grimaldii suggests a differentiation mainly by peadomorphy (progenesis). The two species live in mesobathyal depths, isolated in two separate ocean basins. In the genus Gephyrocrinus , they correspond to divergent phenotypes probably resulting from allopatric speciation after closing of the Pacific-Atlantic pathway ( Améziane & Roux 1997 ). Gephyrocrinus messingi n. sp. differs from Ptilocrinus in having relatively gracile pinnules, highly ornamented aboral cup and tegmen, no free brachials between Br4 and Br9 (except in the juvenile), a series of free brachials usually after Br19, wider interrays, pinnule architecture, flanged aboral border of basal ring, lateral projections on proximal columnals, and stalk symplexies with relatively short crenulae. The holotype shares with species of the subgenus Ptilocrinus a tegmen with orals at the top of regular rows formed by relatively less differentiated cover plates. The Antarctic species Dumetocrinus antarcticus shares with Gephyrocrinus messingi n. sp. a very similar globular inflated tegmen with a verrucose ornamentation, anal sac shorter than oral cone and smooth orals of moderate size ( John 1937 ). Both species have a flanged border at base of aboral cup. D. antarcticus differs mainly in stalk symplexies with a dozen crenular units ( Roux 1980 ), presence of H-shaped plates in genital pinnules (Mironov & Sorokina 1998), and an arm pattern usually without a series of successive brachial pairs (M.R. unpublished observations on all the specimens of the type series). The central eastern Pacific species Calamocrinus diomedae shares with Gephyrocrinus the presence of successive brachial pairs proximally, genital expansion at the pinnule base with numerous lateral plates not in rows, proximal stalk symplexies with 7 crenular units in juveniles, and a flanged aboral border of basal ring ( Agassiz 1892 ; Roux 2004 ). It differs mainly in having divided arms, no lateral plates in the middle and distal parts of the pinnules, and stalk symplexies with up to 16 crenular units in adults. It shares with Gephyrocrinus messingi n. sp. the frequent alternation of brachial pairs and free brachials (a+b c d+e f…) in the mid arm. Occurrence. Northeastern Pacific (off British Columbia and California), at depths from 1,777 to 2,110 m .