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Fig. 2. A, B in Agastograptus, a synonym of Plectograptus (Retiolitidae, Graptolithina)

Fig. 2. A, B. Plectograptus macilentus (Törnquist, 1887), ZPAL G. 27/1; Baltic erratic boulder 46 Jarosławiec (photo D. Bates). A. Reverse view of proximal fragment of immature rhabdosome. B. Inside view showing shape of ancora umbrella and shape of rhabdosome in cross section. C, D. Plectograptus robustus (Obut and Zaslavskaya, 1983). C. ZPAL G.27/2, EEP, Bartoszyce borehole, depth 1627.0 m, obverse view of immature rhabdosome. D. UIGGM SB RAS 251/42−4/1, holotype, Kaliningrad District, North Kaliningrad borehole, depth 2094.0–2105.5 m (courtesy of N. Sennikov). Scale bars 0.5 mm. Abbreviations: a, aperture; ap, apertural process; au, ancora umbrella; l, lip; mv, mid−ventral list; po, proximal orifice; v, virgella.

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Fig. 3. A, H in Agastograptus, a synonym of Plectograptus (Retiolitidae, Graptolithina)

Fig. 3. A, H. Spinograptus munchi (Eisenack, 1951), A. ZPAL G. 27/3, EEP, Bartoszyce borehole, depth 1626.6 m, reverse view of mature rhabdosome. H. ZPAL G. 27/7, EEP Mielnik borehole, depth 1044.0 m, enlargement of paired apertural processes of distal theca. B, E, F. Neogothograptus balticus (Eisenack, 1951), Baltic erratic boulder 46 from Jarosławiec. B, E. ZPAL G. 27/4 mature rhabdosome with appendix (photo D. Bates). B. Reverse view. E. Ventral view of thecae 12 side. F. ZPAL G. 27/5 enlargement of single reticular apertural process. C, G. Spinograptus clathrospinosus (Eisenack, 1951), C. GSC120736, Arctic Canada, Cornwallis Island, AB−97 25 m, stereopair of immature rhabdosome, reverse view (modified after Lenz and KozłowskaDawidziuk 2002: fig. 13: 6). G. ZPAL G. 27/6, EEP, Bartoszyce borehole, depth 1631.2 m, paired apertural processes of medial theca. D. Cometograptus nevadensis (Berry and Murphy, 1975), GSC 99161, Arctic Canada, Cornwallis Island, SBC10E (modified after Lenz 1993: pl. 19: 1), ventro−latral view of rhabdosome. Scale bars 1 mm except for D, F–H which is 0.5 mm. Abbreviations as Fig. 2.

Fig. 3 in Evolution of the retiolitid Neogothograptus (Graptolithina) and its new species from the upper Wenlock of Poland, Baltica

Fig. 3. SEM micrographs showing comparison of the genicular hoods of mature rhabdosomes of Neogothograptus Kozłowska−Dawidziuk, 1995 species (A–D) and Gothograptus nassa Holm, 1890 (E). A, B. Neogothograptus eximinassa Maletz, 2008, Baltic erratic boulder from Wetterhammer, Thuringia, Germany, Colonograptus ludensis–Monograptus gerhardi Biozone. C, D. Neogothograptus reticulatus sp. nov. C. ZPAL G. 41/7, Bartoszyce borehole 1630.7 m, Colonograptus praedeubeli Biozone. D. ZPAL G 41/2, Baltic erratic boulder 59, Jarosławiec, Poland. E. Gothograptus nassa, Bartoszyce borehole 1655.8 m, Pristiograptus dubius– Gothograptus nassa Biozone, whole hood (E1) and enlargement showing bandages covering hood (E2).

Fig. 1 in Evolution of the retiolitid Neogothograptus (Graptolithina) and its new species from the upper Wenlock of Poland, Baltica

Fig. 1. Silurian paleogeographic map, showing occurrences of Gothograptus nassa and Neogothograptus. Localities and graptolite data derived from the following literature sources: 1, Arctic Canada: Lenz 1993; Lenz and Kozłowska−Dawidziuk 2004; 2, Nevada: Berry and Murphy 1975; 3, Southern Sweden (Baltica): Holm 1890; 4, Northeastern Poland (Baltica): Kozłowska−Dawidziuk 1995; 5, United Kingdom: Warren 1971; 6, Southern Portugal: Gutiérrez−Marco et al. 1996; 7, Southern Spain: Gutiérrez−Marco et al. 1996; 8, Thuringia (Saxothuringia): Jaeger 1991; 9, Bohemia: KozłowskaDawidziuk et al. 2001; 10, Kazakhstan: Koren' et al. 2003; 11, Kyrgyzstan: (AL personal observation 1995); 12, South China: Zhang and Lenz 1997; 13, Southeastern Australia: Rickards et al. 1995; 14, Tunisia, Morocco and Libya: Waterlot 1945, Jaeger et al. 1975.

Fig. 7 in Evolution of the retiolitid Neogothograptus (Graptolithina) and its new species from the upper Wenlock of Poland, Baltica

Fig. 7. SEM micrographs of rhabdosome fragments of Neogothograptus reticulatus sp. nov., Bartoszyce borehole 1630.7 m, Colonograptus praedeubeli Biozone. A. Distal end of mature rhabdosome with five pairs of thecae, and beginning of the appendix, ZPAL G. 41/7 (A1); enlargement of distal part showing long reticulated apertural hoods (A2). B. Distal end of young rhabdosome with three pairs of thecae and growing appendix, ZPAL G. 41/8 (B1); enlargement of distal part with small appendix and central nema (B2).

Fig. 6 in Evolution of the retiolitid Neogothograptus (Graptolithina) and its new species from the upper Wenlock of Poland, Baltica

Fig. 6. SEM micrographs of rhabdosomes Neogothograptus reticulatus sp. nov. (A–C, E), and Colonograptus praedeubeli Jaeger, 1990 (F) from Baltic erratic boulder, Jarosławiec 59, Colonograptus praedeubeli Biozone, upper Homerian, Wenlock, Poland. A. Stereopair of lateral view of most distal end with four pairs of thecae, ZPAL G. 41/2. B. Fragment of appendix possibly belonging to Neogothograptus reticulatus, ZPAL G. 41/3. C. Stereopair of lateral view of most distal end with five thecae, with long reticulated hoods, and beginning of the appendix, ZPAL G. 41/4, lateral view (C1), view of the inside (C2). D. Lateral view of proximal end with two pairs of thecae, ZPAL G. 41/5, view of ancora from the inside (D1), enlargement of the hood list with pustules (D2). E. Enlargement of the ancora sleeve list with poorly developed pustules, ZPAL G. 41/6. F. lateral view of Colonograptus praedeubeli, rhabdosome of young colony with two thecae.

Fig. 9 in Evolution of the retiolitid Neogothograptus (Graptolithina) and its new species from the upper Wenlock of Poland, Baltica

Fig. 9. SEM micrographs of fragments of rhabdosomes of Neogothograptus alatiformis Lenz and Kozłowska−Dawidziuk, 2004, Baltic erratic boulder 62 from Jarosławiec, Poland, Ludlow. A. Proximal end with outer ancora, lateral view; ventral view (A1), showing ventral orifice closed by reticulum (A2), enlargement of ancora list (A3). B. Enlargement of appendix, distal view (B1), lateral view of appendix (B2). C. Singular apertural process on geniculum, lip with short mid−ventral visible from inside (C1); inside view of fusellar nature of apertural process (C2). D. Ventral and lateral part of rhabdosome with aperture and apertural process.

Fig. 8 in Evolution of the retiolitid Neogothograptus (Graptolithina) and its new species from the upper Wenlock of Poland, Baltica

Fig. 8. SEM micrographs of rhabdosomes of Neogothograptus thorsteinssoni Lenz and Kozłowska−Dawidziuk, 2004, Bartoszyce borehole 1598.0 m, Neodiversograptus nilssoni Biozone. A. Obverse view of finite rhabdosome with five pairs of thecae and appendix, lateral−ventral view. B. Lateral view of distal end of rhabdosome with appendix and nema (B1); enlargement of distal part of appendix with thick nema (B2). C. Ventral−lateral view of distal part of rhabdosome with appendix. D. Proximal part of reverse side of rhabdosome with three pairs of thecae (D1); enlargement of ancora region with outer ancora, and first theca (D2).

Fig. 5 in Evolution of the retiolitid Neogothograptus (Graptolithina) and its new species from the upper Wenlock of Poland, Baltica

Fig. 5. SEM micrographs of proximal fragment of rhabdosome Neogothograptus reticulatus sp. nov., ZPAL G. 41/1, Bardo, Prągowiec, Holy Cross Mountains, Poland, Colonograptus praedeubeli Biozone. Stereopair of reverse view: ventral view of the thecae 11 side (A), stereopair of obverse view (B); outer ancora edge on thecae 12 side, ancora with outer ancora partly destroyed, view from outside (C), closure of proximal end showing outer ancora and reticulum closing orifices, obverse view (D), inside view howing thecal lip, geniculum, and med−ventral list (E), closure of proximal mid−ventral−list (F).

Fig. 4. Cladistic analysis. A in Evolution of the retiolitid Neogothograptus (Graptolithina) and its new species from the upper Wenlock of Poland, Baltica

Fig. 4. Cladistic analysis. A. Our preferred of four most parsimonious trees (see text for explanation) showing positions of character state changes. Letters (characters) and numbers (states for each character) correspond to codings shown in Appendix 1. Asterisks indicate state changes to a polymorphic condition for groups of taxa above the corresponding node. B. Strict consensus tree for the cladistic analysis of the matrix shown in Appendix 2, all characters unordered and unweighted. Pseudoplectograptus was used as the outgroup taxon. Tree length: 39; consistency index: 0.769; rescaled consistency index: 0.553; retention index: 0.719; homoplasy index: 0.487. Abbreviations: B., Baculograptus; E., Eisenackograptus; G., Gothograptus; N., Neogothograptus.

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Moving towards a better understanding of iterative evolution: an example from the late Silurian Monograptidae (Graptolithina) of the Baltic Basin

Iterative evolution has proved a difficult evolutionary phenomenon to study and interpret. Inferences of causality vary from study to study and quantitatively based phylogenetic reconstruction has never been attempted. In an effort to better understand iterative evolution we employed stratocladistics, gap analysis, and disparity analysis to study the case of the Monograptidae in the aftermath of the late Silurian C. lundgreni extinction event. Our combination of gap analytical and stratocladistic techniques allowed us to elucidate the evolutionary relationships between the studied taxa. Based on our stratocladistic results we recommend the generic reassignment of 5 monograptid taxa. The stratocladistic results, in conjunction with morphological disparity analysis suggest the presence of a persistent developmental potential for the emergence of iteratively evolving characters. This persistent potential appears to be limited by extrinsic ecological constraints, which would have relaxed in the aftermath of the C. lundgreni extinction event. Our findings indicate that iterative evolution in the late Silurian Monograptidae is a product of the interaction of both intrinsic and extrinsic constraints on the acquisition of the iteratively evolving character, with the exact causality being dependent on the particular character.

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Moving towards a better understanding of iterative evolution: an example from the late Silurian Monograptidae (Graptolithina) of the Baltic Basin

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FIGURE 12. Rhabdopleura emancipata n in Four new species and a ribosomal phylogeny of Rhabdopleura (Hemichordata: Graptolithina) from New Zealand, with a review and key to all described extant taxa

FIGURE 12. Rhabdopleura emancipata n. sp., A, B, D, E, paratype NIWA 161566; C, paratype 161211: A, B, distal part of a ringed tube, the bracketed section enlarged in B. C, transmitted-light view of a principal tube (stem) with openings of four ringed tubes all around; tentacles of one young zooid partly emergent; note how black stolon changes position within principal tube; cdc = cone of diaphragm complex. D, close-up of exterior surface of a principal tube showing parallel fusellar annuli marked by thin sutures. E, sclerotized tube, with terminal aperture at left, branching off a principal stolon. Scale bars: A, 200 μm; B, 100 μm; C, 400 μm; D, 100 μm; E, 1 mm.

FIGURE 11. Rhabdopleura emancipata n in Four new species and a ribosomal phylogeny of Rhabdopleura (Hemichordata: Graptolithina) from New Zealand, with a review and key to all described extant taxa

FIGURE 11. Rhabdopleura emancipata n. sp., A, B, holotype NIWA 13590; C, E, paratype 161211; D, paratype NIWA162566: A, B, close-up and whole colony (inset); principal tubes are identifiable in A by the dark-brown stolon that passes through them; abundant ringed tubes diverge almost at right angles from principal tubes. C, transmitted-light view of a principal tube (pt) from which two ringed tubes (rt) diverge and, between them, a branch of the principal tube with a bifurcation of the black stolon (bs); other abbreviations: cdc, cone of diaphragm complex; cs, contractile stalk (gymnocaulus) of zooid; fc, fusellar collar; s, septum. D, SEM of a principal tube (pt) (stem), with its aperture at left, and five ringed tubes in various stages of development. E, transmitted-light view of a principal tube (pt) (stem) and its black stolon (bs) in which are three young zooids (z), the middle one of which shows, from below, the opening of a potential ringed tube (ort). Scale bars: A, 3 mm; B, 3 cm; C‒E, 0.5 mm.

FIGURE 10. Rhabdopleura decipula n in Four new species and a ribosomal phylogeny of Rhabdopleura (Hemichordata: Graptolithina) from New Zealand, with a review and key to all described extant taxa

FIGURE 10. Rhabdopleura decipula n. sp., A, C, D, holotype 162592; B, E, paratype 3 NIWA 162591; F, paratype 4 NIWA 158517; G‒K, paratype 2 NIWA 161213. A, broken-tipped erect tube. B, distal end of young erect tube. C, D, subdistal and middle parts of same fully formed erect tube. E, F, parts of creeping tubes with some point-to-point suture zigzags highlighted. G, a prosicula (ps) and metasicula (ms); H‒K, reflected-light (H, I) and SEM (J, K) images of new colonies, with numbers indicating the inferred budding sequence (subsequent development seems to vary) of creeping tubes; the metasicula produces one or two metasiculae while one side of the prosicula is internally partitioned off to produce both a backwards-directed tube and an opposing creeping tube. Black stolons occur in H and a zooid in I. Scale bars: A, E‒H, 200 μm; B, 100 μm; C, D, K, 50 μm; I, J, 400 μm.

FIGURE 7. Rhabdopleura chathamica n in Four new species and a ribosomal phylogeny of Rhabdopleura (Hemichordata: Graptolithina) from New Zealand, with a review and key to all described extant taxa

FIGURE 7. Rhabdopleura chathamica n. sp., A‒C, F, paratype 90265; D, E, holotype 161214: A, part of colony showing three blind side branches, the proximal part of which is adherent; only one ringed erect tube (et) remains. B, close-up of middle side branch in A; note part of the pectocaulus/black stolon (bs) seen through a tear in the cuticle. C, the longest zooid seen, somewhat fouled and partly twisted in profile. D, non-fouled part of another erect tube showing well-developed fusellar collars. E, fusellar sutures on surface of creeping tube, with some point-to-point suture zigzags highlighted. F, close-up of fusellar sutures seen on adherent tube in B. Scale bars: A, 1 mm; B, 300 μm; C, F, 100 μm; D, 50 μm; E, 200 μm.

FIGURE 5 in Four new species and a ribosomal phylogeny of Rhabdopleura (Hemichordata: Graptolithina) from New Zealand, with a review and key to all described extant taxa

FIGURE 5. Original illustrations of three described species of Rhabdopleura characterized by direct-frontal inception of ringed erect tubes (A‒C). Erect-tube inception in R. compacta (D‒F) appears to be a form of indirect erect-tube inception. Note that the direction of zooid budding is the same in A to C. A, Rhabdopleura mirabilis (from Sars 1872, pl. 1, fig. 5). B, Rhabdopleura annulata (from Norman 1921, fig. 4). C, Rhabdopleura recondita (after Beli et al. 2018, fig. 2C). D‒F, Rhabdopleura compacta (respectively after Hincks 1880, pl. 72, fig. 8; Stebbing 1970b, fig. 1; Stebbing 1970a, fig. 3).

FIGURE 6. Rhabdopleura grimaldii Jullien, 1890 in Four new species and a ribosomal phylogeny of Rhabdopleura (Hemichordata: Graptolithina) from New Zealand, with a review and key to all described extant taxa

FIGURE 6. Rhabdopleura grimaldii Jullien, 1890 (A‒D, syntype MNHN-IB-2014-386) and R. manubialis Jullien & Calvet, 1903 (E, syntype MNHN-IB-2014-387). A, B, oblique views of two erect ringed tubes. C, adherent proximal part of a side branch (apsb), with a tapering pectocaulus (tp) (its side walls appearing as converging brown lines) and the broken base of an erect tube (bbet). D, similar to C, but also showing the creeping tube (ct) from which the broader side branch originated; note the faint outlines of oblique sutures on the creeping tube and side branch. E, erect ringed tube. Scale bars: A, B, 100 μm; C‒E, 200 μm. Images cropped from photos supplied by Pierre Lozuet, MNHN, Paris.

FIGURE 2. Interpretative images illustrating morphological terms and measured characters. A in Four new species and a ribosomal phylogeny of Rhabdopleura (Hemichordata: Graptolithina) from New Zealand, with a review and key to all described extant taxa

FIGURE 2. Interpretative images illustrating morphological terms and measured characters. A, part of creeping tube (ct) of an unidentified Rhabdopleura (NIWA 158518) from Kermadec Ridge, with flat lateral margin (flm), faint oblique fusellar sutures and two ringed erect tubes (et) produced directly from the frontal surface of a creeping tube. B, distal end of an erect tube of Rhabdopleura francesca n. sp. (NIWA 158157), showing a vertical series of ring-like fuselli (f), the rim of each comprising a curled fusellar collar (fc). Tube diameter (td) is measured between fusellar collars; fusellus height (fh) is the distance between the bases of a pair of fusellar collars. C, transmitted-light image of part of a principal ('creeping') tube of R. emancipata n. sp. (NIWA 161211) showing a young zooid with contracted arm tentacles (at), stomach (st), rectum (r) and cephalic shield (cs), part of which is concealed by the reddish-brown stolon (black stolon or pectocaulus). D, aperture of an erect tube of R. francesca n. sp.; note the smooth-surfaced interior devoid of vertical fusellar fibrils. E, part of a creeping tube of an unidentified Rhabdopleura (NIWA 90267) from Cavalli Seamount with frontal fusellar sutures (fs, two arrowed). The white lines show the zigzag (zz) portion of the sutures (note the proximalwards shift to the left), with zigzags rendered as straight lines between points of intersection, regardless of suture curvature, to obtain measured angles (one example shown). F, close-up of part of R. francesca n. sp. (NIWA 158157) showing chains of dark 'dormant buds' (db) lying upon short stretches of the black stolon (bs); walls of enveloping creeping tubes almost invisible in image.

FIGURE 1 in Four new species and a ribosomal phylogeny of Rhabdopleura (Hemichordata: Graptolithina) from New Zealand, with a review and key to all described extant taxa

FIGURE 1. Map showing the localities of four new Rhabdopleura taxa from New Zealand. From north to south these are R. emancipata n. sp., R. francesca n. sp., R. chathamica n. sp. and R. decipula n. sp. The boundary of the Extended Continental Shelf is shown surrounding New Zealand. The grey contour lines show the 1000 m depth interval. The map was generated using ArcGIS Pro.