Feracrinus koslowi, Ameziane & Roux, 2010

Ameziane, Nadia & Roux, Michel, 2010, Stalked crinoids from Tasmanian seamounts. Part 1: Hyocrinidae, Journal of Natural History 45 (3 - 4), pp. 137-170 : 141-159

publication ID	https://doi.org/ 10.1080/00222933.2010.520825
persistent identifier	https://treatment.plazi.org/id/03E687BE-FF92-517A-FDED-FB555249FA31
treatment provided by	Felipe
scientific name	Feracrinus koslowi
status	sp. nov.

Treatment

Feracrinus koslowi View in CoL sp. nov

Analchalypsicrinus sp. Améziane and Roux, 2001:131.

Etymology

This species is named for Anthony Koslow ( CSIRO, Australia) who conducted investigations on the benthic fauna of the seamounts off southern Tasmania .

Material

During the 1997 cruise which investigated Tasmanian seamount fauna, eight specimens were collected, one on Hill D 1, six on Hill V and one on Hill W ( Table 1). The three specimens with stalk and crown from station 69 are designated as the type-series because they demonstrate an ontogenetic sequence. The larger specimen is designated as the holotype. Measurements of main morphological parameters are given in Table 2 for the five specimens which have their crowns preserved .

Diagnosis

A species of Feracrinus with relatively narrow arm bases (ratio of upper radial width to Br1 width 1.8 to 2.7). Brachial width decreasing progressively from proximal to distal arm. Brachial pairs and isolated brachials without conspicuous constriction midway between muscular articulations. Ornamentation variable, brachial without wing-like lateral projections. Beyond Br4, first brachial with two muscular articulations usually from Br11 to Br15, rarely at Br7 or 9, series of more than two successive muscular articulations appearing usually between Br16 and Br26, very rarely before Br11. Proximal part of genital pinnules with fragile H-shaped plates or only one row of lateral plates on each side. Tegmen never inflated with conspicuous bridges between oral cone and arm, up to 15 tegminal plates per inter-radius, orals well developed, anal cone lower or slightly higher than oral cone. Ratio of height to maximum diameter of aboral cup 1.0 to 1.2, ratio of cup height to radial height 1.3 to 1.8, ratio of upper radial ring diameter to upper basal ring diameter 1.26 to 1.47. Basal fused or basal ring with one to three sutures. Proximalmost stalk diameter up to 5.2 mm. Juvenile columnal symplexies with six or seven crenular units composed of one short crenula each. In larger specimens, columnal symplexies with 7 to 10 crenular units of two or three crenulae; beyond minimum stalk diameter, symplexies with regular radial crenulae becoming irregular more distally; typical syzygies with labyrinthic concentric pattern in distal stalk.

Holotype

Museum Victoria registration number: MV F171341. Robust specimen relatively complete ( Figure 2A, B View Figure 2 ), only middle and distal parts of two arms and distal stalk lacking. Arms with dense pinnulation infested by myzostomids; arm width progressively decreasing from proximal (4.0 mm) to distal (3.0 mm at Br20) parts, brachials without wing-like lateral projections; brachial pairs united by synostosis and brachials with two muscular articulations without conspicuous constriction midway between their muscular articulations. Proximal arm pattern always 1+2 3 4 5+6 7+8 9+10 with first pinnule on Br4, beyond Br4 succession of brachial pairs interrupted by successive muscular articulations from Br11, Br13 or Br15, number of successive muscular articulations increasing distally up to five, and more than six on one arm ( Table 3).

Tegmen not inflated. Anal tube conical, height 6.2 mm, slightly higher than oral cone, anal plates progressively decreasing in size from base to top ( Figure 2E View Figure 2 ). Oral cone well developed with finger-like projections irregularly placed; fewer than 15 Notes: Larm, arm length; Lpi, pinnule length; Npi, number of pinnules on each arm side; Wb, first primibrachial width; Wr, upper radial width; Dc, maximum upper diameter of aboral cup; Drb, diameter at radial/basal suture; Hc, height of aboral cup; Hr, radial height; Dp, proximalmost stalk diameter; Dm, minimum stalk diameter; Spec., specimen; HOL, holotype; PA, paratype A; PB, paratype B; 23 and 67, station number where the specimen comes from.

Values are in mm, except for ratios.

St 69 Paratype A Dp = 1.6 Dm = 0.86 Crenular units: 6 (1)

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 30+31 1+2 3 4 5+6 7+8 9+10 11+12 13+14 15 broken

1+2 3 4 5+6 7+8 9+10 11+12 13+14 broken

St 69 Paratype B Dp = 3.4 Dm = 2.2 Crenular units: 7 (1–2) to 9–10 (2–3)

1+2 3 4 5+6 7+8 9 10+11 12+13 14 15+16 17 18+17 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

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 broken

1+2 3 4 5+6 7+8 broken

St 69 Holotype Dp = 5.2 Dm = 3.2 Crenular units: 7 (1–2) to 9 (3–4)

1+2 3 4 5+6 7+8 9+10 11 12+13 14 15+16 17 18 broken

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... 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...

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 broken

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... 30 31+32

Notes: Dp, proximalmost stalk diameter; Dm, minimum stalk diameter.

Values in mm; number underlined indicates the brachial bearing the first pinnule, bold numbers in arm pattern indicate brachials with two muscular articulations, numbers between parentheses give number of crenulae per crenular units.

convex tegminal plates per inter-radius clearly distinct from granulated small plates covering ambulacral bridges ( Figure 2F View Figure 2 ). Aboral cup curved and about as wide as high ( Figure 2A, B View Figure 2 ), height of radial ring along inter-radial suture from 12.7 to 15.0 mm, height of basal ring from 9.3 to 7.0 mm, diameter at base of basal ring 5.3 mm (other measurements see Table 2), narrow proximal arm insertion preserving wide inter-radial space, basal ring showing two inconspicuous sutures.

Oral face of arms, pinnules and bridges supporting ambulacral grooves from orals to brachials covered by numerous thorns or granules; proximal pinnules with lateral finger-like projections ( Figures 2E, F View Figure 2 , 3A View Figure 3 ). Proximal part of genital pinnules with one row of lateral plates on each side; lateral plates with thorns usually in pairs partially fused; one line of thorns bearing on pinnules and one line on lateral plates on each side of a pinnule ( Figure 3A, E View Figure 3 ); proximal cover plates concave with variable sharp terminal projections ( Figure 3C, D View Figure 3 ) forming a crowded scalloped row covering food groove from proximalmost pinnule to arm. Stereome bridge uniting two opposite lateral plates in a single H-shaped ossicle very fragile or absent ( Figure 3E View Figure 3 ). Several genital pinnules partially or completely regenerated, regenerated pinnules smooth without ornamentation ( Figure 3B View Figure 3 ). Brachials without ornamentation on aboral and lateral sides ( Figure 4A–E View Figure 4 ), except two or three short lateral projections near oral crest in proximal arm. On successive brachials bearing pinnules, each pinnule impacting on proximal facet of following brachial with a bevelled edge ( Figure 4A, B View Figure 4 ). Aboral part of brachial facet semi-circular, ventral part with side bearing pinnule less developed than opposite side ( Figure 4C View Figure 4 ). Pinnulars united by flat synostoses having symmetric oral groove ( Figure 4F View Figure 4 ).

Stalk preserved in three fragments for a total length of 189.2 mm. Proximal fragment attached to aboral cup, length 13.3 mm, diameter decreasing from 5.2 mm (proximalmost stalk diameter) to 3.4 mm at 5 mm above irregularly broken distal end, polygonal thin columnals jointed by symplexies with nine crenular units of two or three (inner ring) to three or four (outer ring) crenulae, inner and outer rings of crenulae separated by a discontinuity, claustrum present inside axial canal ( Figure 5A, B View Figure 5 ). Length of middle fragment 35.9 mm, proximal diameter 3.2 mm, distal diameter 3.5 mm, distal columnals united by syzygies of concentric and labyrinthic pattern showing at their centre juvenile symplexial pattern with seven crenular units of two or three crenulae ( Figure 5D View Figure 5 ). Length of distal fragment 140 mm, proximal diameter 3.6 mm, distal diameter 5.3 mm, distal columnals united by syzygies with pentagonal lumen; small inner ring with thin radial pattern, wide middle ring with weak labyrinthic pattern, and outer ring with irregular radial crenulae ( Figure 5C View Figure 5 ).

Paratype A

Museum Victoria registration number: MV F171342. Small juvenile specimen complete ( Figure 2D View Figure 2 ), except for distal part of two arms and distal stalk attachment. Arm pattern ( Table 3) with first pinnule always on Br4, beyond Br4 succession of brachial pairs interrupted by successive muscular articulations from Br15, maximum observed of four successive muscular articulations in one distal arm. Pinnules well differentiated on proximal arm but without genital expansion (immature specimen), cover plates spear-shaped ( Figure 8F View Figure 8 ). Arms and pinnules without ornamentation. Relatively wide arm base and narrow inter-radius. Tegmen height at top of orals 3.4 mm; orals narrow forming a steep cone; height of anal cone 1.9 mm; basal ring with one or two sutures; diameter at base of basal ring 2.0 mm (see Table 2 for other measurements).

Total length of preserved stalk 88.2 mm. Length of proximal fragment attached to aboral cup 25.5 mm, columnal diameter decreasing from 1.6 mm to 0.86 mm at distal end, in proximal part columnals of variable thickness and diameter over 17.6 mm becoming barrel-shaped with symplexies displaying six crenular units of one crenella in distal part ( Figure 5E View Figure 5 ). Length of distal fragment 62.7 mm, distalmost diameter 1.2 mm, columnals remaining barrel-shaped and united by syzygies with irregular radial pattern at distal end ( Figure 5F, G View Figure 5 ).

Paratype B

Museum Victoria registration number: MV F171343 . Specimen of intermediate size between paratype A and holotype ( Figure 2C View Figure 2 ). Granular ornamentation and thorns on arms, pinnules and tegmen less conspicuous than in holotype. Arm pattern ( Table 3) with first pinnule always on Br4, beyond Br4 succession of brachial pairs interrupted by successive muscular articulations usually from Br13, from Br9 on one arm, only two successive muscular articulations alternating with one brachial pair between Br13 and Br25, with a maximum of three successive muscular articulation observed. Main features of pinnules and cover plates as in specimen from station 67 (see Figure 8C,D View Figure 8 ). Height of anal cone 6 mm, base of anal cone occupying only a part of anal inter-radius, anal cone slightly lower than oral cone. Aboral cup globular, lower diameter of basal ring 4.8 mm (see Table 2 for other measurements). Basals fused .

Total length of preserved stalk 282.5 mm. Length of proximal fragment attached to aboral cup 4.5 mm. Length of middle fragment 152 mm, proximal diameter 2.5 mm distal diameter 2.1 mm, several proximal columnals with oval facet of 10 crenular units indicating permanent stalk bending, other proximal columnals having circular symplexial facets with 10 (proximalmost) or nine (following stalk bending) crenular units of two or three crenulae and areola slightly hollowed between crenular units ( Figure 6A, B View Figure 6 ). Length of distal fragment 126 mm, proximal diameter 2.1 mm, distal diameter 3.1 mm, proximal columnal articulated by symplexies with eight crenular units of one or two crenulae becoming irregularly subdivided near outer facet border ( Figure 6C, D View Figure 6 ), distal columnals united by syzygies of concentric labyrinthic pattern preserving at centre juvenile symplexial pattern with seven crenular units of two irregular radial crenulae ( Figure 6E, F View Figure 6 ).

Specimen from station 23

Tasmanian Museum Hobart registration number: TMH H2334. Medium-sized specimen with long stalk, aboral cup and four proximal arms preserved to Br10 or more; fifth arm broken at Br2; stalk separated from crown proximally ( Figure 7D View Figure 7 ). One arm was removed for better observation of oral cone. Tegmen height at top of oral cone 6.2 mm; orals concave, forming a steep pyramid ( Figure 7E View Figure 7 ) as in paratype A; height of anal cone 5.3 mm ( Figure 7F View Figure 7 ); 12–15 tegminal plates per interradius; ornamentation poorly developed. Basals fused or with one inconspicuous suture.

Arm pattern: see Table 4. One arm very unusual with divided short and slender arm at Br15ax; arm ramification gracile (width 1.7 mm) infested by myzostomid and with small pinnules excepting two pinnules of normal size on IIBr3. Pinnules without conspicuous ornamentation like in regenerated pinnule of holotype, proximalmost cover plates strongly concave, forming a crowded scalloped row covering food groove ( Figure 8A View Figure 8 ), lateral plates of genital pinnules without thorns ( Figure 8B View Figure 8 ).

St 23 1 specimen Dp = 3.1 Dm = 1.9 Crenular units: 6 (1–2) to 7 (2–3) - 1 2+3 4+5+6+7 8 9 10 broken

1+2 3 4 5+6 7 8 9 10+11 12 13 14+15ax 16 17 18 19+20 21 22 23+24 25 26 27 28+29... 33+34

1+2 3 4 5+6 7+8 9+10 11 12

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

St 67 1 specimen Dp = 3.4 Dm = 1.8 Crenular units: 9 (1–2)

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

1+2 3 4 5+6 7+8 9+10 11+12 13+14 15 16+17 18 broken

1+2 3 4 5+6 7+8 9+10 11+12 13+14 15 16+17 18 19+20 21 22+23 broken

1+2 3 4 5+6 7+8 9+10 11+12 13+14 15+16 broken

Notes: Dp, proximalmost stalk diameter; Dm, minimum stalk diameter.

Total length of preserved stalk 336 mm, stalk diameter decreasing up to 1.9 mm about 65 mm below basal ring; symplexies with seven crenular units of two or three crenulae and areola slightly hollowed between crenular unit bases ( Figure 9A, B View Figure 9 ); stalk diameter increasing to 2.1 mm about 200 mm more distally with symplexies having seven crenular units of two irregular crenulae tending to form a labyrinthic pattern near outer facet border ( Figure 9C, D View Figure 9 ); distalmost stalk diameter 3.2 mm; distal columnals united by syzygies with labyrinthic and concentric pattern; juvenile symplexial pattern with six crenular units of one or two crenulae preserved at centre ( Figure 9E, F View Figure 9 ).

Specimen from station 45

Museum Victoria registration number: MV F171344. Aboral cup base broken with a few proximal columnals and one stalk fragment. Basals fused or perhaps with one inconspicuous suture in basal ring; lower diameter of basal ring 3.9 mm. Articulation facet at base of basal ring with eight structures divided in two outer branches corresponding to crenular units; areola with eight ligamentary pits (four deeper than others and without galleried stereome) around pentalobate lumen ( Figure 10A, B View Figure 10 ); this facet plays the role of a mould for new columnals appearing below. Thin proximal columnals with eight crenular units of two or three crenulae, new columnal developing from inner areola ring between two pre-existent columnals ( Figure 10C, D View Figure 10 ). Length of stalk fragment 47.8 mm, decreasing in diameter from 3.3 mm to 2.7 mm at distal end; columnals articulated by symplexies with eight crenular units of two or three highly interlocked crenulae.

Specimen from station 67

Museum Tasmanian Hobart registration number: TMH H2335. Complete specimen except distal stalk and distal part of three arms, one arm removed for best observation of anal cone ( Figure 7A View Figure 7 ). See Table 2 and Table 4, respectively, for main measurements and arm pattern. Tegmen height at top of oral cone 6.9 mm, height of anal cone 6.9 mm; tegmen granulated except at upper part of oral cone ( Figure 7B View Figure 7 ); anal cone with coarser granulation ( Figure 7C View Figure 7 ). Basal ring with three sutures.

Middle arm with up to four successive muscular articulations, distal part with series of more than six muscular articulations on one arm only. Lateral plates of genital pinnules with strongly convex outer surface but without thorn ( Figure 8C View Figure 8 ); cover plates always spear-shaped ( Figure 8C, D View Figure 8 ); lateral plates progressively disappearing at about one-third of pinnule length ( Figure 8E View Figure 8 ); distal part of pinnules as in paratype A.

Total length of preserved stalk 125 mm. All the columnals articulated by symplexies with nine crenular units. Thin proximal columnals with a well-developed claustrum, two or three crenulae per crenular unit, more or less hollowed areola between crenular unit bases ( Figure 11A–D). Minimum stalk diameter attained about 20–25 mm below basal ring, displaying symplexies of very regular radiate pattern with one or two crenulae per crenular unit ( Figure 11E, F). Distalmost preserved columnals with articulations intermediate between symplexy and syzygy ( Figure 11E); large inner part symplexial with one or two irregular crenulae per crenular unit ( Figure 11F).

Specimens from station 70

Museum Victoria registration number: MV F171345. Two stalk fragments belonging to different individuals. All columnal facets with seven crenular units. Smallest (juvenile) fragment: length 65 mm, proximal diameter 1.4 mm (probably very close to minimum stalk diameter), distal diameter 1.5 mm, columnals barrel-shaped ( Figure 12A, C View Figure 12 ), proximal symplexies with short and regular radial crenulae (one or two per crenular unit) ( Figure 12B View Figure 12 ), distal preserved columnal with longer and irregular crenulae (two or three per crenular unit) ( Figure 12C, D View Figure 12 ). Largest distal fragment with proximal portion of attachment disc: length 135 mm, proximal diameter 3.2 mm, distal diameter 5.4 mm (just before attachment disc); proximal columnals united by syzygies with labyrinthic concentric pattern, with inner part preserving juvenile symplexial pattern similar to distal symplexies of smallest fragment ( Figure 12E, F View Figure 12 ).

Remarks

In Feracrinus koslowi sp. nov., the aboral cup varies in shape but remains without ornamentation or conspicuous ribs prolonging arm axes. Variation in the ratio of radial width to primibrachial width are always higher than in F. aculeatus . As previously observed (Roux 2002) in the genus Thalassocrinus A.H. Clark, 1911 , the relative width of the proximal arm distinguishes the two species currently known in Feracrinus . In F. koslowi sp. nov., the tegmen is never inflated and the oral cone is always well-developed. Ornamentation of the tegmen, proximal arm and pinnules is highly variable, but lacks the lateral flattened projection on the proximal brachials of the holotype of F. aculeatus . On the holotype of F. koslowi sp. nov., which is strongly ornamented, the pinnule regenerated with smooth surfaces documents that differences in ornamentation do not necessarily reflect differences in individual genomes.

Beyond Br4, which always bears the first pinnule, F. koslowi usually bears three to five successive brachial pairs before the next brachial with two muscular articulations while F. aculeatus usually has one to three. Series of more than three successive muscular articulations always appear beyond Br24. In the specimen from station 23, Br15 bears an imperfect ramification probably developed during arm or pinnule regeneration. John (1937) and Roux (1980) described such abnormal ramifications in Dumetocrinus antarcticus (Bather, 1908) and Gephyrocrinus grimaldii Koehler and Bather, 1902 respectively. In hyocrinids, only Calamocrinus diomedae normally exhibits divided arms ( Agassiz 1892); immature juveniles with undivided arms indicate that arms divide during ontogeny ( Roux 2004), either from transformation of a pinnule into an arm or by regeneration after breaking ( Gislèn 1924). Strong changes in coverplate shape within or between individuals demonstrate that this character is not useful as a diagnostic feature within the genus Feracrinus . Mironov and Sorokina (1998a, b) illustrated H-shaped plates in genital pinnules of F. aculeatus . The pinnule architecture of F. koslowi sp. nov. could allow formation of H-shaped plates but their development usually remains incomplete.

Are there significant changes in arm pattern during growth? The type series ( Table 3), in which the three specimens were presumed to have lived under the same environmental constraints, suggests a decrease in the number of brachial pairs following Br4 from five or more in the small paratype to four or fewer in the two larger specimens. This seems to be confirmed by the specimen from station 23 (three or fewer). However, the specimen from station 67, which is about the same size as paratype B, bears three arms with five or more pairs and only two arms with four. Is this due to different environmental constraints? More specimens are required to give evidence of reduction of brachial pair number through ontogeny.

Our detailed study of the F. koslowi sp. nov. stalk shows the greatest diversity currently known in columnal articulation patterns in any single hyocrinid species. Proximal symplexies have a regular radial crenularium, with the most regular in the segment with the minimum diameter ( Figures 9A, B View Figure 9 , 11E, F). Symplexial crenulae become irregular below this segment ( Figures 6D View Figure 6 , 9D View Figure 9 ), weakly tending towards the hieroglyph-like crenulae which develop in F. aculeatus . Syzygies with a labyrinthic concentric crenularium ( Figures 5D View Figure 5 , 6E View Figure 6 , 9E View Figure 9 ) develop distally; more regular radial syzygies ( Figure 5C View Figure 5 ) are present in the distalmost articulations. The number of crenular units varies from six to ten, with one to four crenulae per crenular unit. As documented in other stalked crinoids ( Améziane and Roux 2005; David et al. 2006), functional columnal articulations depend on environment, especially current regimen. So, the symplexial pattern of the proximal stalk tends to converge whereas few or no functional articulations in the middle and distal stalk offer divergent characters useful for taxonomy. The trend to hieroglyph-like symplexial crenulae and the labyrinthic feature of distal syzygies are only known in Feracrinus . The complex and relatively regular labyrinthic concentric pattern of syzygial facets in F. koslowi sp. nov. seems to be a typical character of this species. Moreover, the place where the articulation type changes varies along the stalk from one specimen to another, probably related to different environmental constraints throughout ontogeny as has been observed in Guillecrinus ( Améziane and Roux, 2005) .

In terms of columnal ontogeny, main character trajectories can be deduced from our observations on F. koslowi sp. nov. During a crinoid’s life, new columnals appear at the top of the stalk, just under the basal ring. So the oldest columnals are at the distal end of the stalk and the youngest just below the aboral cup. Frequently, in a given crinoid columnal, the axial canal diameter increases by resorption of perilumen stereome ( Améziane and Roux 2005). During columnal growth in hyocrinids, the axial canal diameter maintains the same size as when the columnal first developed at the top of the stalk without any stereome resorption. Consequently, along a given hyocrinid stalk, axial canal diameter increases from distal to proximal columnals ( Figures 5 View Figure 5 , 6 View Figure 6 , 9 View Figure 9 , 11, 12 View Figure 12 ), and in proximal columnals from small juveniles ( Figure 5E View Figure 5 ) to large adults ( Figure 5A View Figure 5 ). As proximal columnal diameter becomes larger with specimen growth, the number of radial crenulae can increase from six ( Figure 5E View Figure 5 ) to 33 ( Figure 5A View Figure 5 ) with a distribution into various numbers of crenular units from six ( Figure 5E View Figure 5 ) to 10 ( Figure 6A View Figure 6 ). In the proxistele, each columnal only grows in thickness (height). Consequently, stalk diameter decreases from the proximalmost columnal (Dp) toward the stalk segment with a minimum value (Dm). So, the proximal stalk remains the most flexible portion where regular symplexial articulations develop. Beyond Dm, columnal diameter increases while growth in height decreases. In this transitional portion where flexibility becomes reduced, the symplexial crenularium develops irregular crenulae weakly tending to a hieroglyph-like appearance. When growth in height stops, the symplexial pattern is only preserved in the facet centre, while diameter growth allows development of the syzygial crenularium with a labyrinthic concentric pattern (from the youngest to the oldest columnals, see respectively Figures 6E, F View Figure 6 ; 11G, H; 5D View Figure 5 and 9E, F View Figure 9 ). Distalmost columnals, the oldest, were never articulated by symplexies but by syzygies ( Figure 5F, G View Figure 5 ). As their diameter increases, syzygies keep a predominantly radial pattern ( Figure 5C View Figure 5 ).