Allonnia tintinopsis, Bengtson & Collins, 2015

Bengtson, S & Collins, D, 2015, Chancelloriids of the Cambrian Burgess Shale, Palaeontologia Electronica 10 (14), pp. 1-67 : 21-36

Allonnia tintinopsis n.sp.

Figures 2 ; 3 ; 12 (part); 17–30; 31.1–31.3; 32–37

http://zoobank.org/NomenclaturalActs/ 52051170-F28B- 4A48-9DD8-B76979C3AD5A

Chancelloria eros new species ( Walcott, 1920, partim; pl. 88:1, 1a, 1b, 1d, 1e).

Chancelloria eros Walcott, 1920 ( Briggs et al., 1994; figure 176).

Chancelloria ( Bengtson, 2000; figure 1A; figure 12, partim).

Derivation of the Name. From Tintin, the comicbook hero of Hergé (Georges Remi), and Greek - opsis, like, alluding to the pronounced apical tuft of this species.

Holotype. ROM 62527 [1] ( Figure 16.1 , right; 16.2, 16.3).

Figured Paratypes. USNM 66526, 66528. ROM 49573, 49582, 49584, 49587, 49588, 49589,

BENGTSON & COLLINS: CHANCELLORIIDS

49596, 49600, 49601, 49602, 49603, 49605, 49606, 49607, 49608, 49609, 49610, 49612, 49614, 49615, 49616, 49620, 49621, 57574, 62514, 62515, 62516, 62517, 62518, 62519, 62520, 62521, 62523, 62524, 62525, 62526, 62527[2], 62536, 62537, 62585, 62586, 62587, 62591.

Diagnosis. Species of Allonnia with slender, regularly dispersed 3+0 sclerites and pronounced apical tuft formed by modified body sclerites. Ray length of fully developed body sclerites 3–3.8 mm; basal width of rays about 200 µm. Abapical end of body commonly anchored to skeletal debris, to sponges, or to other chancelloriids.

Description. This is the most common chancelloriid in the Burgess Shale, characterized by a strictly regulated scleritome with exclusively 3+0 body sclerites and a prominent palisade of spines (the apical tuft) around the apical orifice. The body is usually club-shaped, with the widest part near the apex and abapically tapering to a point or a prolonged stalk.

Two of Walcott’s (1920) figured syntypes of Chancelloria eros belong to this species, namely his pl. 88:1, 1a ( USNM 66526 ; Figure 2 herein) and pl. 88:1d, 1e ( USNM 66528 ; Figure 3 herein) .

The holotype ( Figure 16.1 , right; 16.2, 16.3) is a large specimen, about 200 mm long and 55 mm wide. The body contour is clearly outlined by an integument that forms a film, darker than the surrounding matrix. The abapical part appears incomplete but forms a cylindrical stalk more than 30 mm long and ca 18 mm wide. The sclerites are distinctly preserved, with a uniform size and shape across the whole body: each one has three slender rays, two lateral and one ascending, each up to 3.8

PALAEO- ELECTRONICA.ORG

mm long and basally up to about 200 µm wide ( Figure 16.3 ). They have the typical lyre shape seen in most shale-preserved specimens. This shape is due to the selective preservation of the curved lateral rays vs. the ascending ray, which is usually seen only where the sclerites are laterally compressed at the edges of the flattened specimen ( Figure 16.3 , right). The lateral rays form a mutual angle of ca 70° and curve somewhat toward each other in the plane formed by the two rays. The plane of the rays forms a 0°–35° angle to the body surface. The ascending rays diverge basally at 80°–120° from the plane of the lateral rays, and then curve toward the apical end of the body. The sclerites are semiregularly distributed over the body surface in a rhombic pattern, at intervals of about 1.5–3 mm in the wider parts of the body; in the narrower abapical portion the sclerites are more densely positioned. The apically facing body surface shows a denser palisade of sclerites, and centrally there is an 8 mm wide region characterized by an aggregation of thin, parallel outwardfacing rays ( Figure 16.2 ). This clearly corresponds to the tuft seen in most specimens (see below).

A second specimen ( Figure 16.1 , left) is preserved side-by-side with the holotype. It is 88 mm long and 32 mm wide. Its body shape is similar to that of the holotype, but there is no discernible stalk; instead, the abapical end appears to narrow to a point. The apical end is not exposed. The

BENGTSON & COLLINS: CHANCELLORIIDS sclerite density is higher than in the holotype, the interval between sclerite bases being roughly a millimetre in the wider parts of the body; toward the narrow abapical end of the body the density becomes even higher, resulting in a jumbled mass of sclerites.

The body shape in most of the larger specimens is similar to that of C. eros , i.e. club-shaped with an abapical taper or stalk. Smaller specimens tend to be more, spindle-shaped (e.g., Figure 17.2 ), with an acute apical contour, whereas larger ones may have a more flattened apical surface (e.g., Figure 16.1 , right). There is some variation in body proportions, from broad (e.g., Figure 16.1 ) to more narrow ( Figure 2.1 ).

An even greater variability exists in the expression of the stalk, from a narrow taper and apparent absence of a distinct stalk (e.g., Figures 16.1 , left; 18), to a well-developed stalk, up to 40 cm long (e.g., Figure 19 ). The stalk differs from the more apical parts of the body only by its smaller diameter and greater crowding of sclerites. Figure 20 shows a diversity of stalk expression and body shape, from a thin flexible stalk attached to a large, club-shaped body ( Figure 20.1 ) to a 67 mm long hose-like body (probably incomplete in its lower parts) that in itself has the dimensions and sclerite characteristics of a stalk ( Figure 20.2 ). The specimen in Figure 20.3 and 20.4 has an apical bulb-like portion, with relatively scarcely distributed sclerites, and a constricted abapical portion, with a dense sclerite covering. These features strongly suggest that the stalk is not a permanent structure, but represents a temporary contraction of the body wall, starting from the abapical part. See further discussion of this feature in the section “Body shape and attachment.”

Unlike the scleritome of Chancelloria eros , the sclerites in the Allonnia tintinopsis scleritome are of a constant size within most parts of the specimens. The exceptions are in the abapical part where the sclerites are somewhat smaller, and the apical part, where the apical tuft is formed by modified sclerites. Figure 18 shows the maximum ray length of sclerites at various distances from the abapical end in a small and a large specimen. The sclerite size increases gradually from the abapical end toward the apex, but at a distance of about 20 mm from the lower end, the maximum size of ca 3 mm ray length has been reached. The sclerites of the small specimen cluster with those of the correspondingly sized abapical part of the larger specimen.

The apical tuft is a conspicuous feature in most specimens. It is usually expressed as a sclerite-dense ring, about 3–5 mm in diameter, around a circular field more-or-less devoid of sclerites ( Figures 20.3 ; 21–23 ; 24.1, 24.3 ; 25.1 ). Fine rays typically form an upright palisade-like structure (e.g., Figures 17.4, 17.5 ; 21.8, 21.9 ; 22.1; 22.3 ; 23.1 ), but commonly they converge upwards to form a teepee-like structure (e.g., Figure 21.11, 21.12 ). Where the apex of the specimen is obliquely compressed, the fine rays can be seen to cover the sclerite-free area in a more-or-less organized fashion ( Figure 21.8–21.10 ). In one obliquely compressed specimen ( Figure 26 ) the fine rays are radially directed toward the centre of the ring, seemingly covering the central area as a diaphragm shutter.

Although the basal portions of the tuft sclerites are seldom clearly visible, they sometimes seem to widen into a knob-like end ( Figures 21.12 ; 22.3 ). An isolated three-rayed sclerite adjacent to the apical tuft in one specimen shows one long ascending ray and two very short lateral rays ( Figure 22.2 ). This occurrence suggests a morphological transition from the normal body sclerites to the unirayed sclerites making up the tuft palisade. In the specimen showing spines closing the central area ( Figure 26 ), the spines making up the tuft do not show a clearly defined base, but rather merge into a mass of fine-grained pyrite ( Figure 26.3 , left). Because of the oblique compression of this specimen, the three-rayed body sclerites adjacent to the apical tuft are preserved with all their rays visible at the base ( Figure 26.2, 26.3 ). They have a more robust appearance than the tuft spines, but this is largely due to the fact that they represent proximal portions of the rays; the more distal ray parts of the body sclerites that are occasionally preserved are as thin as the tuft sclerites ( Figure 26.2 ).

One specimen ( ROM 62591 ; Figure 23.2, 23.3 ) has a peculiar fabric in the tuft in the form of ca. 0.5 mm broad, rounded sheets surrounding the fine spines. These structures have a distinct boundary and appear to imbricate. The material has a different reflectance than most of the skin ( Figure 23.2 , left and bottom), but this could be an effect of preservation, as there are areas surrounding the tuft that have a similar sheen. Although

PALAEO- ELECTRONICA.ORG these structures might conceivably represent soft tentacle-like organs, they are more likely to represent diagenetic haloes around the spines, such that are commonly present around the rays of chancelloriid body sclerites ( Figures 2.1 ; 3 ; 10 ; 23.2 , left; 25.2; 27.1, 27.2; 28.2; 29) and tuft sclerites ( Figure 30.1 ). The tight packing of the tuft spines seen in other well-preserved specimens (e.g., Figures 22 ; 26 ) in any case does not leave room for surrounding soft tissues.

The apical structure represented by the ring forming the tuft is typically more heavily mineralized than the rest of the body, giving it a more solid appearance ( Figures 3.1, 3.2 ; 17 ; 20.3 ; 21.1–21.3, 21.6, 21.11 ; 22.1 ; 24.1–3 ; 25.1 ; 26 ; 30 ). In specimens with pyritized sclerites and tufts, this feature is often expressed as an increasingly higher concentration of pyrite grains toward the apical end ( Figures 17 ; 21.1 ; 26 ; 30.2; 30.4 ; 31.2 ). In combination with the lack of distinct boundaries of the ring-like structure, this suggests that the latter structure does not represent a discrete organ but is rather a taphonomic phenomenon caused by a higher concentration of organic matter in the adapical region.

The skin is variably preserved but is commonly seen as a smooth surface with different colour or reflectance from that of the surrounding matrix. Occasionally it is longitudinally folded ( Figure 32.1, 32.2 ). In most cases, no fine structure is

BENGTSON & COLLINS: CHANCELLORIIDS visible, but a few specimens show a granular surface ( Figure 31.1–31.3 ) similar to that of Archiasterella coriacea ( Figure 31.4 ). No evidence for regular openings is visible over the body surface, with the exception of the ring-shaped apical structure. The sclerite-free area inside the ring in several specimens has a different colour or reflectance from that of the surrounding skin ( Figures 21.2– 21.3, 21.10 ; 24.1, 24.3 ; 30.3 ). This suggests the presence of a body opening surrounded by the fine rays of the tuft.

The lower end of the specimen is in several specimens associated with shell debris or some other object. Lumps of shell debris are seen at the abapical ends of two specimens in Figure 33 , and Figure 28.1 shows a specimen with two large hyolith conchs in the abapical end. The end of the stalk in the specimen in Figure 19 has a patch of dark material that differs in colour from the rest of the specimen, but it is not clear whether this represents a solid object.

The large slab ROM 62585 ( Figure 33 ) contains an association of 11 specimens of the general club shape characteristic of most large forms. Except for one specimen (lower left in figure), the bodies on this slab are strictly aligned; however, four of them lie with the apical end to the right (as oriented in Figure 33.2 ), and six with that end to the left. The specimens range from 45 mm to 226 mm in length, and they all taper abapically to nearly a point. A lump of shell debris at the lower end of the largest and one of the smaller specimens (grey patches in Figure 33.2 ) is interpreted to represent an anchoring root bulb; a third such lump on the same slab does not have any visible connection with an Allonnia individual .

In addition to the evidence for anchoring by attachment to shell debris in the soft sediment, Allonnia tintinopsis is frequently preserved in a way that suggests that it attached to other sedentary organisms, in particular the sponge Vauxia and other chancelloriids. Figure 27.1–27.2 shows a specimen with a stalk-like abapical end that is strongly bent towards an assemblage of Vauxia . Although no direct attachment surface can be seen, the specimen appears complete and abuts directly to the sponge. It was therefore likely attached to the latter. Similarly, Figure 27.3 shows a branching Vauxia from which at least three Al. tintinopsis radiate. This is hardly a chance association, but rather evidence that Allonnia attached to the sponge. Probable direct attachments of Allonnia to Vauxia are also seen in Figures 17.4 ; 28.2 ; and 34.

Other associations with Vauxia are common, in which it is not possible to determine whether the individuals were attached to each other ( Figures 12.1 ; 25.1 ; 29 ) or whether the roles of the two taxa may even be reversed ( Figures 25.2 ; 35 ). The slab shown in Figure 29 suggests a complex thicket of intertwined Allonnia and Vauxia where both taxa appear to have been serving as substrate for the other.

Apart from the sponge Vauxia and other chancelloriids, there is evidence that brachiopod epizoans also used live chancelloriids for attachment. Micromitra burgessensis is known to attach to sponge spines, in particular those of Pirania ( Whittington, 1985; Caron, 2005). This brachiopod is also found in close association with Allonnia tintinopsis , in positions that make it likely that it attached directly to the spines of the chancelloriid ( Figures 24.1, 24.3, 24.4 ; 36 ). (See also the similar association of C. eros with the brachiopod Acrothyra gregaria described above, Figure 9.1–9.3 .)

A life reconstruction of Allonnia tintinopsis growing on Vauxia is shown in Figure 37 .

Comparison. Among Allonnia species known from whole-body preservation, Al. tintinopsis differs from Al. phrixothrix in having sclerites only about half as large and a more pronounced apical tuft.

Figures

FIGURE 2. Allonnia tintinopsis n.sp., USNM 66526 (specimen figured as Chancelloria eros by Walcott, 1920, pl. 88:1, 1a, and by Briggs et al., 1994, figure 176). 1. Wet. 2, 3. Details of 1 (positions marked by frames), dry.

FIGURE 3. Allonnia tintinopsis n.sp., USNM 66528, upper part of body (specimen figured as Chancelloria eros by Walcott, 1920, pl. 88:1d, 1e). 1. Wet. 2. Detail of 1 (position marked by frame), wet. 3. Detail of 2 (position marked by frame), wet.

FIGURE 9. Chancelloria eros Walcott, 1920. 1–3. ROM 57604, BW -130. Specimens of the lingulate brachiopod Acrothyra gregaria appear to be attached to the spines of the Chancelloria. The brachiopods are concentrated to what is interpreted as the apical part of the chancelloriid body. 1. Wet. 2. Detail of 1 (position marked by frame), dry. 3. Detail of 2 (position marked by frame), dry. 4. ROM 63055, ST, dry.

FIGURE 10. Chancelloria eros Walcott, 1920. ROM 62534, RT. 1. Wet. 2. Detail of 1 (position marked by frame), wet. Note the common presence of 3+0 Allonnia-type sclerites (arrows) in a scleritome dominated by 5–7+1 Chancelloria- type sclerites.

FIGURE 12. Allonnia tintinopsis n.sp. intergrown with or superimposed on Chancelloria eros Walcott, 1920. 1–3. ROM 49605(2) (intergrown with a specimen of Vauxia), RQ 9.2. 1. Same as figure 12B in Bengtson, 2000; see that paper for details on settings. 2, 3. Details of 1 (positions marked by frames), dry. 4–6. ROM 62537B, RQ 8.4. 4. Wet. 5, 6. Details of 4 (positions marked by frames), dry. Net-like patches are fragments of Micromitra shells.

FIGURE 16. Allonnia tintinopsis n.sp., ROM 62527, part (1, 2) and counterpart (3), BW -110. 1. The larger specimen to the right in 1 is the holotype (ROM 62527[1]). 2. Holotype, detail of apical part (position marked in 1), with tuft. 3. Detail of lower part of body of holotype (counterpart; position on part marked in 1), showing morphology and arrangement of sclerites. Small letters at mid right denote lateral (L) and ascending (A) rays of selected sclerites. All pictures taken wet.

FIGURE 17. Allonnia tintinopsis n.sp. Apical tufts and concentration gradient of pyrite. 1. ROM 62524A (also in Figure 21.1), RQ 8.7, wet. 2. ROM 62516B, RQ 8.8, wet. 3. ROM 62519B, RQ 8.2, wet. 4. ROM 62586, wet. 5. ROM 62517, RQ 8.8, wet.

FIGURE 18. Ray length against distance from base in Allonnia tintinopsis n.sp. ROM 49610A, RQ 11.4 (left; white squares) and ROM 49607A, RQ 10.7 (right; black circles).

FIGURE 19. Allonnia tintinopsis n.sp. with stalk-like constriction. ROM 49573, ST. 1. Complete specimen, dry. 2. Detail of 1 (position marked by frame), dry, showing lower part of stalk with densely packed sclerites and debris.

FIGURE 20. Allonnia tintinopsis n.sp. with stalk-like constrictions. 1. ROM 49616B, RQ 9.1, dry. 2. ROM 49596A, RQ 8.4, dry. 3, 4. ROM 49603, RQ 8.9. 3, Dry/pol. 4. Detail of 3 (position marked by frame), dry/pol.

FIGURE 21. Allonnia tintinopsis n.sp. Apical tufts and orifices. 1. ROM 62524A (also in Figure 17.1), RQ 8.7, dry. 2. ROM 49608a, RT, dry/pol. 3. ROM 49608b, RT, dry/pol. 4. ROM 49607A, RQ 10.7, wet/pol. 5. ROM 62525B, RQ 8.4, dry. 6. ROM 62525B, RQ 8.4, dry/pol. 7. ROM 62520B (also in Figure 24.3), RQ 9.0, wet. 8, 9. ROM 62587, RQ 8.4, wet/pol (8), wet (9). 10. ROM 49614B, RQ 9.0, dry/pol. 11, 12. ROM 49620B (counterpart to the upper right specimen in Figure 27.3), RQ 9.0, 11. Dry/pol. 12. Detail of 11 (position marked by frame), dry/pol. Scale bars in all pictures equal 1 mm.

FIGURE 22. Allonnia tintinopsis n.sp. ROM 49612A, RQ 9.8, dry/pol. 1. Apical part of body, with tuft. 2, 3. Details of 1 (positions marked by frames).

FIGURE 23. Allonnia tintinopsis n.sp. Apical tufts. 1. ROM 49605(1), RQ 9.2, wet/pol. 2, 3. ROM 62591, UE. 2. Wet. 3. Detail of 2 (position marked by frame), wet.

FIGURE 24. Allonnia tintinopsis n.sp. intergrown with Vauxia (1, 2) and having Micromitra attached to the spines (1, 3, 4). 1. ROM 49588B, RQ 9.0, wet/pol. 2. ROM 49606, RQ 8.9, wet. 3. ROM 62520B (also in Figure 21.7), RQ 9.0, wet. 4. ROM 62515B, RQ 8.8, wet.

FIGURE 25. Allonnia tintinopsis n.sp. associated with Vauxia. 1. ROM 49587B, RQ 8.3, dry. 2. ROM 49584A, RQ 8.1, wet.

FIGURE 26. Allonnia tintinopsis n.sp. ROM 57574, RQ 8.5. Apical tuft and orifice. 1. Dry. 2–4. Details of preceding pictures (positions marked by frames), dry.

FIGURE 27. Allonnia tintinopsis n.sp., attachment to Vauxia. 1–2. ROM 62523A, RQ 8.4. 1. Wet. 2. Detail of 1 (position marked by frame), wet. 3. ROM 49620A (upper right-hand specimen is part to the one in Figure 21.11–12), RQ 9.0, wet.

FIGURE 28. Allonnia tintinopsis n.sp., two specimens on the same slab showing probable attachment to hyoliths (1, wet) and Vauxia (2, wet). ROM 62518A, RQ 8.2. Inset in 2 (dry) shows blowup of isolated, probably extraneous, Chancelloria-like sclerite in Allonnia scleritome.

FIGURE 29. Intergrowths of Allonnia tintinopsis n.sp. and Vauxia. Part, ROM 62526A (2) and counterpart, ROM 62526B (1, 3), RQ 8.4. 1. Wet. 2. Detail of part (position marked by frame in 1), wet. 3. Detail of 1 (position marked by frame), wet.

FIGURE 30. Allonnia tintinopsis n.sp, apical orifice with pyrite concentration. 1. ROM 49609A, RQ 9.0, dry. 2. ROM 62536, BW -400, wet/pol. 3. ROM 49582B, RQ 9.0, wet/pol. 4. ROM 49601A, RQ 9.7 (figure 1A2 in Bengtson, 2000; see that paper for details on settings).

FIGURE 31. Integument structure of Allonnia and Archiasterella. 1. Allonnia tintinopsis n.sp. ROM 62514B, RQ 9.8, dry. 2, 3. Allonnia tintinopsis n.sp., ROM 49600A, UE. 2. Dry. 3. Detail of 2 (position marked by frame), dry. 4. Archiasterella coriacea n.sp., holotype, ROM 62531A, BW -130, dry.

FIGURE 32. Allonnia tintinopsis n.sp. 1. ROM 49615A, WT, dry/pol. 2. ROM 49621, UE, dry.

FIGURE 33. Association of Allonnia tintinopsis n.sp., bodies and attachments, on bedding slab. ROM 62585, RQ 8.4. 1. Part; arrow points to specimen represented by counterpart in 3, dry. 2. Tracing of bodies (red; darker tones toward the apex) and root bulbs (grey), based on both part and counterpart. 3. Counterpart of specimen with root bulb marked by arrow in 1, dry.

FIGURE 35. Intergrowth of Allonnia tintinopsis n.sp. with Vauxia. ROM 62521B, RQ 8.4. 1. Dry. 2. Detail of 1 (position marked by frame), dry.

FIGURE 36. Allonnia tintinopsis n.sp. together with Micromitra shells and carapace of Isoxys. ROM 49602B, RQ 8.7, dry.

FIGURE 37. Life reconstruction of Allonnia tintinopsis, n.sp., growing on the sponge Vauxia. Artwork Pollyanna von Knorring.