Diplacanthus tenuistriatus Traquair, 1894

Burrow, Carole, Newman, Michael & Davidson, Robert, 2016, The diplacanthid fishes (Acanthodii, Diplacanthiformes, Diplacanthidae) from the Middle Devonian of Scotland, Palaeontologia Electronica 19, pp. 1-83 : 17-34

Diplacanthus tenuistriatus Traquair, 1894

Figure 1.3 -44, Figure 13 , Figure 14 , Figure 15,

Figure 16 , Figure 17 , Figure 18 , Figure 19 , Figure 20 , Figure 21 , Figure 22 , Figure 23

1892 Homacanthus borealis Traquair ; Traquair, p. 205, pl. 8.

1895 Diplacanthus tenuistriatus ; Traquair, p. 244.

1900 Diplacanthus tenuistriatus ; Wandolleck, p. 360, 365.

1904 D. tenuistriatus ; Goodchild, p. 595.

1907 Diplacanthus tenuistriatus ; Dean, p. 216, 222.

1923 Diplacanthus tenuistriatus ; MacFarlane, p. 303.

1937 Diplacanthus tenuistriatus ; Westoll, p. 22.

1940 Homacanthus gracilis (EICHW.) , in part; Gross, p. 21, pl. 1, 2.

1954 Diplacanthus tenuistriatus Agassiz ; Waterston, p. 12.

FIGURE 9. Line drawings of serial transverse sections through pectoral girdle elements of Diplacanthus crassisimus ; sketch of whole specimen NMS G. 2014.4.30 used to denote position of the sections shown in 2, 3 (mirror image sketch in latter). 1, serial destructive Sollas sections through admedian spine from west of Castletown, Caithness. 2, thin sections A–L through an isolated pectoral girdle complex NMS G.2014.33.8, from west of Castletown harbour. 3, Sollas sections 1–15 through an isolated juvenile pectoral girdle complex (without pectoral spine) from west of Castletown, Caithness. Abbreviations: adm.s=admedian spine; p.fs=pectoral fin spine; scap=scapula.

? 1973 Homacanthus gracilis , in part; Gross, p. 86.

1973 Diplacanthus? carinatus Gross , in part; Gross, p. 72-73, pl. 36.8.

1976 Diplacanthus tenuistriatus Traquair ; Paton, p. 11-12.

1979 Diplacanthus tenuistriatus Traquair ; Denison, p. 32.

1979 Homacanthus gracilis , in part; Denison, fig. 32J.

1985 Diplacanthus? carinatus Gross , in part; Valiukevičius, pl. 1.3, 1.5, pl. 3.1, 2, pl. 11.9

1997 D. tenuistriatus ; Young, p. 48.

1999 D. tenuistriatus Traquair, 1894 ; Dineley, p. 3.

2006 akantoodi somused; Kleesment, Nestor, and

Soesoo, p. 4 top figure.

2001 D. tenuistriatus ; Hanke, Davis, and Wilson,

p. 751.

2005 Diplacanthus tenuistriatus (Traquair) ; Newman and Dean, p. 3, 4, 5.

2010 Diplacanthus tenuistriatus Traquair, 1894 ;

Newman, p. 12, 13, figs. 18, 19, 20.

Type Material. Syntypes NMS G.1859.33.90 (counterpart NMS G.1859.33.91) from Cromarty , Moray , NMS G. 1892.8.6 (counterpart NMS G. 1892.8.7) from Gamrie, Banff and NMS G.1891.92.340 ( Figure 1.4 ) from Gamrie, Banff .

Referred Material. The following are all the known articulated specimens: from Achanarras Quarry, Caithness , NMS G. 1897.55.1 (part), NMS G. 1897.55.2 (counterpart) and NHM P.22198; from Tynet Burn, Moray, NMS G. 1870.14.144 and NMS G.Canon Kyle no. 1; from Gamrie, Banffshire NMS G. 1892.8.8 (part) and NMS G. 1892.8.9 (counterpart) . Disarticulated remains consisting of spines and pectoral girdle complexes include: from Marwick Bay , Orkney, QM F58024 , NMS G. 2014.4.18 , NMS G. 2014.4.20 , NMS G. 2014.4.23 , NMS G.2014.7.35, NMS G.2014.7.36, NMS G.2014.15.21, NMS G.2014.15.22, NMS G.2014.20.20, NMS G.2014.44.5; from Appat Hill, Caithness, NMS G.1901.153.1; from Birsay, Orkney, NMS G.1898.163.2; from North Ronaldsay , Orkney, NMS G.2014.33.1; from Flashes, Hoy, Orkney, NMS G. 2014.4.27 .

Distribution within the Orcadian Basin ( Figure 2 ). Diplacanthus tenuistriatus is the rarest of the diplacanthid species. It is found in some of the Moray Firth nodule beds including Gamrie, Cromarty, and Tynet Burn. One articulated specimen NMS.G1879.55.1, 2 is known from Achanarras Quarry. From Caithness there are also three isolated spines NMS G1892.91.1 from Lybster (holotype of Homacanthus borealis , Figure 1.3 ), NMS G 1901.153.1 from Appat Hill ( Figure 14.5 ), NMS.G.1965.36 from Taldale Quarry, as well as a pectoral girdle complex NMS G.1898.152 from Brims Ness. In Orkney the species is also rare and mostly represented by isolated spines found with the placoderm Dickosteus threiplandi ( Miles and Westoll, 1963) in deposits of the Upper Stromness Flagstone Formation. The species has not been found in the Sandwick fish bed. Recently a spine (NMS.G.2014.33.1, Figure 16.7 ) was collected on the island of North Ronaldsay in the Middle Rousay Formation, occurring with the placoderm Millerosteus minor ( Miller, 1858) .

Revised Diagnosis. Diplacanthus with spines ornamented with finely striated, closeset longitudinal ridges; pectoral spines have five to nine ridges per side, and paired rows of denticles along the whole length of the exserted portion of the spine, with larger denticles distally and smaller close set denticles proximally; admedian spines about a third the length of the pectoral spines; prepelvic spines slightly shorter than pelvic spines; median spines with long insertion, about a quarter to a third the total length of the spine; anal spine shows moderate curvature; grooves between spine ridges subcircular or flask-shaped in cross-section; one circumorbital plate round the anterodorsal quarter of the orbit; scale crowns with U- or V-shaped straight or sinuous ridges fanning out from the posteromedian ridge and often bifurcating towards the lateral edges; scale crowns are formed of mesodentine, lacking wide radial and ascending canals other than a few canals opening low in the neck.

Description. Head Region. ( Figure 13.4 ) Diplacanthus tenuistriatus closely resembles D. crassisimus , differing in the characters noted in the diagnosis. A few specimens have poorly preserved elements on the head. The one large circumorbital plate is anterodorsally positioned and about a quarter the circumference of the orbit. The occlusal plates are slender and about the length of the orbit. Cheek plates appear to be shorter than the occlusal plates.

Morphology of the Spines. ( Figures 13 , 14 , 15) Most distinguishing characters for Diplacanthus tennuistriatus are spine features. Compared with spines of D. crassisimus in D. tenuistriatus the furrows between longitudinal ridges on the sides are are much narrower ( Figures 14 , 15) and the flattened surfaces of the ribs exhibit a delicate striation (Figure 15.4).

FIGURE 15. Diplacanthus tenuistriatus anterior dorsal fin spines. 1, NMS G.2014.7.35 from Marwick, Orkney. 2–4, NMS G.2014.44.5 from Marwick, Orkney: 2, complete specimen in matrix; 3, magnified view of proximal exserted part; 4, magnified view of the same area. Scale bars equal 1 cm in 1–3; 1 mm in 4.

The large fish NMS G.1897.55.1, 2 ( Figure 13.1-3 ) has a preserved length from the tip of the tail to the base of the anterior dorsal spine of about 280 mm and an estimated total length of about 350 mm, and the spines are rather short in proportion to the dimensions of the fish, compared with Diplacanthus crassisimus . Isolated spines ( Figures 14 , 15), of roughly the same size as those on NMS G.1897.55.1 and 2, are regarded as mature.

The pectoral spine of Diplacanthus tenuistriatus has a rather strong posteriorly directed curvature and an asymmetrical cross section. The main pulp canal is closed over the total length of the exserted part. The denticles in the double row along the posterior edge are larger distally, regularly spaced c. 0.9 mm apart, and smaller proximally, c. 0.6 mm apart ( Figure 14.1-3 ). The pectoral spines are characterized by narrow furrows between the flattened lateral ridges, with a micro-ornament of delicate striations ( Figure 14.3 ). The deep furrows also tend to close over proximally. Ridge number ranges from five to nine, increasing with size of the spines, and often with one more ridge on the upper (dorsally oriented) more convex side ( Figure 14.4 ). The base of the pectoral spine fits in a socket formed mainly by the scapulocoracoid and partly by the lateral edge of the pinnal plate ( Figure 14.7 ). The admedian spine is ankylosed with two elements of the girdle: a dermal plate on the procoracoid and the dermal pinnal plate.

The anterior dorsal fin spine (Figure 15) is the sturdiest of the median spines. In lateral view the spine is almost straight along the posterior side and slightly curved along the leading edge. The inserted part comprises about one fourth of the total length and is subtriangular in shape with a concave anterior margin, deepening towards the insertion-exsertion boundary. The boundary line between these parts is oblique, resulting from the slanting position in life. In cross section, the height:width ratio varies from about 1.5 near the tip to about 1.8 near the insertion. Total length of the spine is about 10 times the maximum height in cross section.

The broad, open main pulp canal of the inserted part extends as an open canal over a short distance in the proximal exserted part of the spine, beyond which it is closed. The posterior face over the main pulp canal is slightly concave with a broad central ridge lengthwise along the midline, with a narrow central groove. The leading edge ridge is rounded and extends over the full length of the exserted part. The lateral ridges, almost parallel to the anterior ridge, increase in number proximally associated with the growth of the spine. There are no ridges or only one or two on each side towards the spine tip. The ridges are rounded in cross section distally but become flattened proximally, increasing in number to nine or 10, comparable to mature anterior dorsal spines of Diplacanthus crassisimus . The number of ridges can vary on either side of the spine. Depth of the furrows between the ribs increases proximally, often closing over completely close to the insertion/ exsertion boundary. Growth lines on the exserted part, parallelling the insertion-exsertion boundary, are visible on better preserved spines (Figure 15.3).

The posterior dorsal fin spine ( Figure 13.1, 13.4 ) is shorter than the anterior dorsal spine, and the number of lateral ridges is considerably less, with a maximum of only four or five per side. The length to maximum depth ratio is c. 13:1; height:width proportion is 1.4 near the tip and 1.3 near the insertion. Both anterior (leading) and posterior (trailing) edges of the spine are 'bent' at the insertion-exsertion boundary, so that the spine is angled back relative to the anterior dorsal spine ( Figure 13.1, 13.4 ). The anal fin spine is strongly curved and more slender than the posterior dorsal spine, with four lateral ridges on each side. Length to maximum depth ratio is c. 16:1, height:width proportion varies from about 1.2 near the tip to about 1.0 near the insertion. The main pulp canal remains open over a third of the exserted part.

The paired pelvic fin spines are less strongly curved than the anal spine and are about two thirds its length, with only two or three lateral ridges. The prepelvic spines are relatively small and of the same shape as the admedian spines, being rather flat, sharply pointed near the posteriorly directed tip and broadly rounded near the laterally expanded base.

The very fine striations on the flattened surface of the ridges mentioned by Traquair (1894) occur in all our studied spines, even on the narrow ridges of the admedian spine. In cross sections the striae show as sharp crests, separated by concave, shallow grooves ( Figure 16.4 ). The crests occur at rather irregular intervals, separated between about 40 μm and 80 μm from the next crest. A conspicuous feature of the striae is that they are not all parallel with the lengthwise direction of the ridges, sometimes being oblique bundles over the full width of a rib, or as a chevron like ornamentation, or as a few radiating lines; they never branch (Figure 15.4).

Histology of the Spines. ( Figures 16 , 17 ) In Diplacanthus tenuistriatus the median, pectoral, and admedian spines all have at least one accessory pulp canal above the main canal. This accessory pulp canal is often somewhat irregular in cross section and although much smaller than the main pulp canal, its diameter is relatively large when compared with the same canal in Rhadinacanthus longispinus . The main pulp canals ( Figure 16.5, 16.7 ) lack the well-developed lamellar infill seen in spines of D. crassisimus . Trabecular dentine forms the inserted parts of the median and pectoral spines and surrounds the accessory pulp canal, with radially arranged vascular canals extending from the more cancellous inner osteodentine. Ornament ridges are formed of osteodentine with fine dentine tubules radiating out to the surface from a network leading to the vascular canals ( Figure 16.3-4 ). The dentine of the ridges has a sharp boundary with a thin outer layer that covers their exterior surface. It is this thin layer on which the superficial striae are developed, and which can cover over the deep grooves between the ridges ( Figure 16.6 ). Small canals run from the vascular canals and open out in the deep grooves between the ribs.

Shoulder Girdle Complex. ( Figures 18 , 19 , 20 ) In the endoskeleton, the scapular shaft of the scapulocoracoid has a vertical, swollen ridge between the broad posterior flange and the narrower postbranchial flange ( Figure 18.1, 18.4 ). The ridge is hollow and always calcite filled. A notch separates the postbranchial flange from the coracoid, with scapula, coracoids, and procoracoid forming a single element. The proximal end of the pectoral spine is rigidly fixed in a socket formed by the pinnal plate and scapulocoracoid ( Figures 18.9 , 19 ).

The dermal shoulder girdle complex comprises an anterior ventral plate, pinnal plate, admedian spine, with a thin, lamellar plate covering the visceral side of these three elements ( Figures 18.4 , 19 ). A wedge of the ventral plate surrounds the proximal part of the admedian spine. The ornament on the ridges of the admedian spine is identical to that of the scales at their bases ( Figure 18.2 ). The pinnal plate lateral to the admedian spine bears ordered, closeset small scales, comparable to normal body scales ( Figure 18.3, 18.6 -8). The pinnal plate is concave and has a triangular shape.

Morphology of the Scales. ( Figures 21.1-3 , 22.2- 3 , 23 ) The outline of the scale crowns of Diplacanthus tenuistriatus is roughly identical to those of the other Middle Devonian Diplacanthidae . The anterior margin is evenly rounded, the lateral corners are more sharply rounded, and the somewhat concave posterolateral margins join in a sharp point. The anterior half of the crown is ornamented with U-shaped or V-shaped ridges, the open side anterior ( Figure 23 ). These ridges are fewer than in D. crassisimus and much less regularly placed. The ridges in the anterior part of the crown fan out towards the lateral corners, where they often bifurcate. In top view the shape of these ridges is often highly irregular, some may be S-shaped, the next ones curved in different directions. The crown has a high sharp median crest running along the posterior half. The crest starts in the anterior part of the crown with two of the V-shaped anterior ridges joining to form the ridge, with the crest increasing in height from anterior to posterior ( Figure 23.8 ). The transverse ridges are serrated like those of D. crassisimus , inclined posteriorly, and overlap ridges behind them on the posterior half of the crown surface. The posterior margins of the scales are only rarely strongly denticulated ( Figure 23.11 ). The neck of the scales is markedly concave all round, with a few buttresses on both anterior and posterior faces which bifurcate into a large number of much smaller ridges, each of them supporting one of the ribs of the crown surface ( Figure 23.1, 23.15 ). In cross section the neck and base are oval in shape, wider than long. The base and the neck are always below the anterior part of the crown and the posterior part of the crown rises above the level of the rest of the scale. The basal surface of the scale is not usually flat as in D. crassisimus , but convex centrally and flattening out towards the marked base-neck rim.

Scale morphology is markedly constant over the flanks, with a sharp transition between body scales and the much smaller scales on the fin webs ( Figure 13.3 ). Fin web scale rows are parallel to the spine on the median fins, and parallel to the body on the pelvic fins ( Figure 13.1-3 ). The position of the lateral line cannot be determined, indicating it is only edged by normal flank scales. The caudal fin shows the same zonation as in other acanthodians such as Euthacanthus macnicoli Powrie, 1864 ( Newman et al., 2014, figure 12).

Histology of the Scales. ( Figures 21.4 -9, 22.4-8, 22.11-16) In Diplacanthus tenuistriatus the ascending canals in the neck and horizontal canals in the crown are narrower than those in D. crassisimus and Rhadinacanthus longispinus . Fine dentinal tubules with sparsely distributed lacunae extend from the narrow canals, forming a mesodentinal network. The five to eight crown growth zones each have a separate network ( Figure 22.5, 22.13 ). In the older growth zones, long dentinal tubules reach further towards the crown centre than in younger growth zones ( Figure 22.4 ). As a result the newer ridges grew mainly by horizontal addition, not by superposition of new ridges above older ones.

Two dentine tubules rise up from lacunae in the neck, then loop twice horizontally near the anterior edge of the crown, where they again join into lacunal widenings, regularly spaced along the anterior edge of the growth zone. From these lacunae, one or two long tubules extend towards the centre of the scale below one or two of the grooves between the ridges on the crown surface. Along their length, which may exceed 250 μm, swollen nodes or lacunae are sometimes present from which short, fine tubules extend out. The long tubules terminate in tufts of repeatedly branching, ever finer tubules, rising up and back into the ridges of the crown surface.

Short horizontal tubules lead off more irregularly occurring lacunae in the posterior parts of the crown. Relatively wide radial canals with a maximum diameter of about 10-12 μm open out low between the neck buttresses. There are only two or three of these radial canals in the posterior neck and occasionally one or two shorter ones anteriorly ( Figure 22.4, 22.12 ). The canals lie over the boundary between the base of the neck and the base cone, with smaller, interconnecting dentine tubules leading off them horizontally and vertically, ascending into the growth zones of the neck. Other fine dendritic dentine tubules, sometimes with lacunal widenings, open directly to the outside of the neck, again between the buttresses, and lead up to form tufts in the growth zones of the neck. Wide circular canals, low in the crown, have narrower canals traversing growth zones and rising up towards the crown surface, branching into finer tubules ( Figure 22.4, 22.14 ).

The top surface of the scale base has a rather flat conical shape ( Figure 22.13-16 ). Cell lacunae are absent, and rare canals of Williamson extend through the base. Laminar layers forming the base are more or less parallel to the lower side, visible as a very faint banding under normal white light. With crossed polars the scale base exhibits conein-cone sheets of isopedin-like light and dark bands, the cones parallel with the top cone ( Figure 22.13 ). Vertical sections show up to seven darker bands, with other banding perpendicular to the parallel bands. These bandings correspond to the layout of Sharpey's fibre bundles through the base (see Burrow, 2001, figure 5).

Remarks. Diplacanthus tenuistriatus shows closest similarity to D. crassisimus in the layout of the pectoral girdle, spine ornament, and scale structure. Traquair (1894), in his short but concise description of Diplacanthus tenuistriatus , mentioned a number of distinguishing features, mostly concerning the spines. He compared the spines of

PE Note: Erratum to Burrow et al., 2016

10 April 2016

The caption of Figure 20 was misprinted in Burrow, Carole, den Blaauwen, Jan, Newman, Michael, and Davidson, Robert. 2016. The diplacanthid fishes ( Acanthodii, Diplacanthiformes, Diplacanthidae ) from the Middle Devonian of Scotland. Palaeontologia Electronica 19.1.10A: 1- 83

palaeo-electronica.org/content/2016/1398-scottish-diplacanthid-fishes

On page 30, Figure 20 has the caption for figure 30 and a duplicate Figure 30 appears with the caption for Figure 20 ( Figure 30 appears correctly on page 42). The following is the correct caption for Figure 20 .

the new species with those of D. striatus (= D. crassisimus ) and stated that in D. tenuistriatus the longitudinal ridges on the sides are less numerous and broader, the furrows between the ridges much narrower, and the flattened surfaces of the ribs exhibit a delicate striation. Of these features, the observation that ribs are less numerous is only true in immature specimens.

The pectoral spine of Diplacanthus tenuistriatus has several features in common with the pectoral spines of the other Scottish Middle Devonian diplacanthids: the rather strong posteriorly directed curvature, the asymmetrical cross section, the main pulp canal closed over the total length of the exserted part, and the double row of recurved denticles along the posterior edge. Some of the isolated spines from the Middle Devonian of the Baltic, previously assigned to Homacanthus gracilis , are pectoral spines of D. tenuistriatus . As noted above, these can be distinguished from those of D. crassisimus by the posterior denticles extending most of the length of the spine, and by having fine striations on the ornament ridges (e.g., Gross, 1940, plate 1.2, 1.1, respectively).

Traquair (1894) gave only a short, superficial description of the scales of his new species, stating that they were similar to those of Diplacanthus striatus (= D. crassisimus ). The sculpture of the crown surface is completely different from the crown in Rhadinacanthus longispinus . Gross (1973, p. 72, 73) erected a new species Diplacanthus? carinatus for relatively large scales with a more robust sculpture than he recognized in D. striatus scales. We identify these scales from the Narva–Burtnieki Regional Stages (Eifelian) in the Baltic (e.g., Gross, 1973, plate 38.9) as D. tennuistriatus . More scales from the same deposits which Valiukevičius (1985, plate 1.3, 1.5, 3.1-2, 11.9) assigned to D.? carinatus are also here considered to be from D. tenuistriatus , as well as scales (including GIT 730- 3: Kleesment et al., 2006, top figure p. 4) from the Givetian Härma beds of Burtnieki Regional Stage, Karksi outcrop, southern Estonia catalogued as Diplacanthus carinatus .

Figures

FIGURE 1. Type specimens of Scottish Middle Devonian diplacanthids: 1, Diplacanthus crassisimus (Duff, 1842) holotype NMS G.1891.92.333, from Tynet Burn, Moray; 2, Rhadinacanthus longispinus (Agassiz, 1844) holotype NMS G.1953.4.3, from Cromarty, Ross and Cromarty; 3, Homacanthus borealis holotype spine NMS G.1892.91.1, from Lybster, Caithness; 4, Diplacanthus tenuistriatus (Traquair, 1894) syntype NMS G.1891.92.340, from Gamrie, Banffshire. Scale bars equal 1 cm.

FIGURE 2. 1, Site map indicating the most important localities with Middle Devonian diplacanthids on northern Scot- land; 2, biostratigraphic table of diplacanthid occurrences in the Orcadian Basin of northern Scotland.

FIGURE 13. Diplacanthus tenuistriatus morphology. 1, NMS G.1897.55.2, counterpart of a headless large specimen from Achanarras Quarry, Caithness; 2, 3, NMS G.1897.55.1 (the part of NMS G.1897.55.2): 2, caudal fin, anal fin spine and fin web and right pelvic fin spine and fin web; 3, posterior dorsal fin spine and fin web; 4, NMS G.1870.14.144 from Tynet Burn, Moray, head and pectoral region. Scale bars equal 1 cm. Abbreviations: ad.fs=anterior dorsal fin spine; adm.s=admedian spine; ck.p=cheek plate; co.p=circumorbital plate; cor=coracoid; lt.sc=left scapula; lt.p.fs= left pectoral fin spine; oc=occlusal plate; p.p=pinnal plate; prepelv.s=prepelvic spines; rt.sc=right scapula.

FIGURE 14. Diplacanthus tenuistriatus pectoral fin spines. 1–4, spine QM F58024 from Marwick, Orkney: 1, complete spine, dorsal surface; 2, ventral surface of spine; 3, recurved denticles on posterior edges of spine; 4, transverse natural fracture surface of distal part of spine, at point arrowed in (2); 5, NMS G.1901.153.1 from Appat Hill, Caithness; 6, NMS G.1898.163.2 from Birsay, Orkney; 7, NMS G.2014.4.18, from Marwick, Orkney, spine attached to pinnal plate. Scale bars equal 1 cm for 1, 2, 5–7; 1 mm for 3, 4.

FIGURE 16. Diplacanthus tenuistriatus fin spine histology. 1–4, pectoral spine NMS G.2014.7.36 from Marwick, Orkney; 1–4, transverse section through the pectoral spine and the posterior end of the pinnal plate; 5, 6, anterior dorsal spine NMS G.2014.7.35 from Marwick Orkney: midspine transverse section. 7, NMS G.2014.33.1, midspine transverse section of anterior dorsal spine from North Ronaldsay, Orkney. Scale bars equal 1 mm in 1, 2, 5, 7; 0.1 mm in 3, 4, 6.

FIGURE 17. Drawings of transverse sections through Diplacanthus tenuistriatus pectoral and anterior dorsal fin spines. 1, 2, pectoral fin spine NMS G.2014.7.36 from Marwick, Orkney: 1, through pectoral spine and posterior end of pinnal plate; 2, slightly distal to the latter section; 3, 4, anterior dorsal fin spine NMS G.2014.7.35 from Marwick, Orkney; 3, midspine; 4, slightly proximal to latter section. Scale bars equal 1 mm. Abbreviations: cc=central pulp canal; e=enameloid; gl=growth line; ost=osteodentine; p.p=pinnal plate; uc=upper longitudinal canal. Arrows point to junction between pectoral fin spine and pinnal plate.

FIGURE 18. Diplacanthus tenuistriatus isolated shoulder girdle complexes. 1–4, NMS G.2014.15.21 from Marwick, Orkney: 1, external surface of scapulocoracoid, pectoral fin spine, pinnal plate and admedian spine; 2, admedian spine; 3, 4, scale-like ornament on pinnal plate; 5, NMS G.2014.15.22 from Marwick, Orkney, internal surface; 6–9, transverse sections of NMS G.2014.4.20 from Marwick, Orkney: 6, pinnal plate; 7, multiple odontode on plate; 8, scalelike ornament; 9, transverse section through pinnal plate, pectoral fin spine base, scapulocoracoid and perichondral bone sheet; 10, 11, NMS G.2014.4.27 from Flashes, Hoy, Orkney, transverse section through base of admedian spine and inner perichondral bone sheet; 10, whole width; 11, scale-like ornament in groove. Scale bars equal 1 cm in 1, 5; 5.0 mm in 2; 1.0 mm in 3, 4, 6; 0.5 mm in 9, 10; 0.1 mm in 7, 8, 11; 0.05 mm in 4.

FIGURE 19. Drawings of serial sections through Diplacanthus tenuistriatus shoulder girdle complexes from Marwick, Orkney. 1, schematic drawing of the external view of shoulder girdle complex NMS G.2014.4.21, showing levels at which transverse sections were made. 2, schematic drawing of the inner view of complex NMS G.2014.15.22. A2–F1 is the section series through the admedian spine on NMS G.2014.4.27; I1 is a section through the pectoral fin base enclosed by surrounding plates on NMS G.2014.4.27; I2, J2B, and J2A are sections through the admedian spine, pinnal plate, pectoral fin, base of scapulocoracoid and perichondral bone of the coracoid of NMS G.2014.4.20; 10A and 10B are sections through the girdle complex NMS G.2014.4.23; K2, L1, M2 and O1 are serial sections through the scapulocoracoid and associated structures of NMS G.2014.20.20. Scale bars equal 5 mm. Anatomical abbreviations: adm.s=admedian spine; pch.b=perichondral bone layer; p.fs=pectoral fin spine; p.p=pinnal plate; sc=scales; scap=scapula; scap.c=central pulp cavity of scapula shaft. Length given for each spine.

FIGURE 20. Reconstruction of the shoulder girdle region in Diplacanthus tenuistriatus. 1, lateral view. 2, ventral view. Dark grey fill indicates dermal elements, light grey fill indicates endoskeletal elements.

FIGURE 21. Diplacanthus tenuistriatus specimens from Achanarras Quarry, Caithness, squamation and scale histology. 1, NMS G.1897.55.2 (Figure 13.1), impression of squamation anterior to base of posterior dorsal fin spine; 2, 3, NMS G.1897.55.1 (Figure 13.2), squamation above the anal fin, scale crown detail partly obscured by matrix; 4–9, NMS G.1897.55.1, serial sections from patch of midflank squamation: 4, 5, vertical transverse section of scale; 6, 7, vertical longitudinal section of scale; 8, vertical longitudinal section of scale; 9, horizontal section near the level of the base/neck rim of scale. Scale bars equal 1 cm in 1; 1 mm in 2–3; 0.1 mm in 4–9. Arrows indicate anterior direction, where relevant.

FIGURE 22. Diplacanthus tenuistriatus squamation and histology of scales from Tynet Burn and Gamrie. 1–8, NMS G.Canon Kyle no. 1 from Tynet Burn: 1, postpectoral–caudal peduncle region; 2, mid-body squamation; 3, scale crown; 4, vertical transverse section of scale from caudal region (area A); 5, vertical longitudinal section of scale from area A; 6, horizontal section through crown base, scale from posterior to ad.fs (area B); 7, mid-crown horizontal section, area B; 8, upper crown horizontal section, area B. 9–16, NMS G.1892.8.9 from Gamrie, Banffshire: 9, complete specimen; 10–16, sections of scales from upper flank area between ad.fs and pd.fs (area A) and lower flank in front of a.fs (area B); 10, calcified cartilage globules, posterior end of area B; 11, horizontal section through scale neck, posterior end of area B; 12, vertical longitudinal section, area A; 13, vertical transverse section, area A; 14, vertical longitudinal section, area A; 15, transverse section, area A; 16, vertical oblique section, area A. Scale bars equal 1 cm in 1, 9; 1 mm in 2-3; 0.1 mm in 4–8, 10–16. Abbreviations: a.fs=anal fin spine; pd.fs=posterior dorsal fin spine. Arrows indicate anterior direction, where relevant.

FIGURE 23. Scanning Electron Micrographs of Diplacanthus tenuistriatus scales. 1–4, NMS G.Canon Kyle no. 1 from Tynet Burn, Moray, scales slide NMS G.Canon Kyle no. 1.1, from dorsal side posterior to ad.fs, SEMs: 1, anterior view with broken crown; 2, 3, posterocrown and anterocrown views with end of posterior crown broken off; 4, posterior view. 5–13, NMS G.1892.8.9 from Gamrie, Banffshire, SEMs: 5, 6, 13–16, scales slide NMS G.1892.8.9.17: 5, crown view; 6, anterocrown view; 13, patch of scales in matrix, crown view; 14, crown view; 15, lateral view; 16, posterior view. 7–12, scales slide NMS G.1892.8.9.18: 7, crown view; 8, anterior view; 9, posterior view; 10, anterolateral view; 11, 12, posterobasal view and closeup of base surface. Scale bars equal 1 mm for 13; 0.3 mm for 1–11, 14–16; 0.1 mm for 12.

FIGURE 30. Rhadinacanthus longispinus median fin spines from mature fish, transverse section drawings. 1, 2, posterior dorsal spine NMS G.2014.4.33 from the slates west of East Murkle Bay, Caithness: 1, spine showing position of sections; 2, sections 1–8. 3, section of posterior dorsal spine NMS G.2014.33.2 from North Ronaldsay. 4, section of anterior dorsal spine NMS G.2014.11.1 from Broad Taing, Orkney. Scale bars equal 1 cm in 1; 5 mm in 2; 1 mm in 3, 4.