DOI: 10.5061/dryad.868sm
title: Data from: Ontogeny, morphology and taxonomy of the soft-bodied Cambrian ‘mollusc’ Wiwaxia

description: The soft-bodied Cambrian organism Wiwaxia poses a taxonomic conundrum. Its
 imbricated dorsal scleritome suggests a relationship with the polychaete
 annelid worms, whereas its mouthparts and naked ventral surface invite
 comparison with the molluscan radula and foot. 476 new and existing
 specimens from the 505-Myr-old Burgess Shale cast fresh light on
 Wiwaxia's sclerites and scleritome. My observations illuminate the
 diversity within the genus and demonstrate that Wiwaxia did not undergo
 discrete moult stages; rather, its scleritome developed gradually, with
 piecewise addition and replacement of individually secreted sclerites. I
 recognize a digestive tract and creeping foot in Wiwaxia, solidifying its
 relationship with the contemporary Odontogriphus. Similarities between the
 scleritomes of Wiwaxia, halkieriids, Polyplacophora and Aplacophora hint
 that the taxa are related. A molluscan affinity is robustly established,
 and Wiwaxia provides a good fossil proxy for the ancestral aculiferan –
 and perhaps molluscan – body plan.
description: SEM of
 NMNH229901The smallest known
 specimen of _Wiwaxia corrugata_; relative to body length, dorsal sclerites
 are vast229901_0056.g.tifMicrograph of NMNH229901Low-quality light micrograph of 229901. For scale please see accompanying SEM.USNM_229901_X31_006.tifSEM close-up of NMNH 229901, showing two sclerites229901_0058.tifSEM enlargement of NMNH 229901, showing pustules on sclerites229901_0059.tifSEM enlargement of NMNH 229901, showing reliefBSE in shadow mode.229901_0060.tifSEM enlargement of NMNH 229901, showing sclerite with longitudinal pyrite crystals229901_0061.g2.tifSEM enlargement of NMNH 229901 (posterior)Showing ventral sclerites229901_0062.g.tifSEM of NMNH194274Specimen length ~5mm; dorsal scleritome well preserved, showing ribbing patterns and arrangement of sclerites. Backscatter (compo)194724_0041.g.tifSEM of NMNH194274 (BSE - shadow)Specimen length ~5mm; dorsal scleritome well preserved, showing ribbing patterns and arrangement of sclerites. Backscatter (shadow)194724_0042.g.tifSEM of NMNH199969 - isolated sclerite containing acicular pyrite199969_0080.g.tifSEM enlargement of NMNH199969 - tip of isolated sclerite containing acicular pyrite199969_0082.g.tifSEM of NMNH198674, showing acicular pyrite in sclerites198674_0112.g.tifSEM of NMNH198674, showing acicular pyrite in sclerites - wide field of view198674_0117.g.tifSEM of NMNH198674, showing acicular pyrite in sclerites - wider field of viewNote three-dimensionality of specimen; lower sclerites are out of focus.198674_0116.g.tifSEM enlargement of NMNH198674, showing well-developed acicular crystals (Fig. 2D)198674_0113.g.tifSEM enlargement of NMNH198674, showing well-developed acicular crystals in multiple sclerites (Fig. 2D)198674_0115.g.tifSEM enlargement of NMNH198674, showing distribution of acicular crystals in sclerite ribs198674_0125.g.tifSEM of NMNH198674, showing sclerites with varying degrees of pyritization; cf. Fig. 2ERegion of Fig. 2E in top centre of image198674_0127.g.tifSEM enlargement of NMNH198674, showing lineations in carbon parallel to acicular pyrite crystals (Fig 2A)198674_0131.g.tifSEM enlargement of NMNH198674, showing lineations in carbon parallel to acicular pyrite crystals (Fig 2B)198674_0130.g.tifSEM of NMNH198662, isolated Wiwaxia scleriteShowing acicular pyrite and later spheroidal overgrowths; note the shape of the end of the sclerite. The microvillar fabric, although not evident in the carbon film, is picked out by the pyrite needles.NMNH198662_001.g.tifSEM of Burgessochaeta, NMNH198634 (Fig. 2G)Note the framboidal form of pyrite in chaetae.198634_627.g.tifSEM enlargement of Burgessochaeta, NMNH198634 (Fig. 2H)198634_630.g.tifSEM of Burgessochaeta, NMNH198634Further chaetae with similar preservationNMNH198634_620.g.tifSEM enlargement of Burgessochaeta, NMNH198634, showing framboidal pyrite in chaetae198634_618.g.tifChaetae of a typical Canadia specimen (NMNH199771); SEMChaetae are replaced by 'massive' pyrite with no obvious crystals. Note that occasional Wiwaxia specimens showed a similar preservational style.199771_803.g.tifPart of ROM57195, Wiwaxia, containing amorphous pyriteEmphasizing that pyrite is not always associated with an acicular habit.ROM57195.g.tifROM 57195 (Fig. 3A), colour image highlighting pyritizationROM 57195.JPGROM 61512 (Fig. 3B) – 'juvenile' specimen, partly enrolled (colour image file)WT90-0185_614 615.grainextract.JPGROM 61649 (Fig. 3D) – Juvenile specimen with faint trace of footJuvenile specimen, preserved sublaterally; mouthparts are visible to anterior, with dark transverse trace underneath, interpreted as anterior margin of foot. See also wet image.ROM 61649 dry.g.JPGROM 61649 (Fig. 3D) – Juvenile specimen with faint trace of foot (wet)Juvenile specimen, preserved sublaterally; mouthparts are visible to anterior, with dark transverse trace underneath, interpreted as anterior margin of foot. See also dry image.ROM 61649 wet.g.JPGROM 61151 (Fig. 3G) – Mature specimen, with incipient spines, and partial scleritome exposing underlying tissueWQ00-1886_657g ge 658g.g.JPGROM 62273 (Fig. 3I) – posterior portion of specimen (dorsal view), showing imbrication of ventral scleritesWT90-1446_452.g.JPGROM 56965 (Fig. 5A) – partially disaggregated scleritomeROM 56965_652.g.JPGUSNM 199953 (Fig. 5B) – lateral group of scleritesUSNM 199953.g.tifROM 61510 (Fig. 5C) – showing depth of scleritome98-1116B ROM 61510_953.g.JPGROM 61510 (counterpart)The plane of splitting passed close to the dorsal surface – hence the depth of sclerites on the part, and the spaces between sclerites on this counterpart.ROM 61510.g.JPG3D model of Wiwaxia infant (Fig. 6A)3D model file used to generate Figure 6A. Blender file format (blender.org).Wiwaxia infant.blend3D model of Wiwaxia juvenile (Fig. 6B)3D model file used to generate Figure 6B. Blender file format (blender.org).Wiwaxia juvenile.blend3D model of mature Wiwaxia (Fig. 6C)3D model file used to generate Figure 6C. Blender file format (blender.org).Wiwaxia mature.blendNMNH 200101 (Fig. 7A) – "moulting" specimenNote that gut (pinker) can be traced along length of specimen. Mouthparts are only visible in the anterior of the specimen.NMNH 200101_003.g.tifNMNH 200101 (Fig. 7A) – Interference imageInterference image highlights distinct preservation of gut, confirming its continuity into the posterior of the specimen. The pronounced nature of the mouthparts heightens confidence that there are genuinely no mouthparts further posteriad.USNM_200101p_X8_003-BexR.g2.tifNMNH 200101 – SEM of anterior region showing mouthpartsMouthparts stand out as carbon films.200101cp_0035.tifNMNH 200101 – SEM of posterior regionSclerites are picked out by faint pyrite layer, but carbonaceous mouthparts are demonstrably absent.200101cp_0034.tifROM 61701 (Fig. 7B) – showing axial trace (gut)ROM 61701_666.g.JPGROM 61515 (Fig. 7C) – OdontogriphusWQ94-1498A_719 gex 720.JPGROM 57714 (Fig. 7D) – OdontogriphusShowing mouthparts and gutWQ95-2130 ROM 57714_616 div 617.g.JPGROM_57715 (Fig. 7E) – Odontogriphus, partially decayed specimenROM_57715.g.JPGROM 61519 (Fig. 8A) – Wiwaxia, terminal view, showing footWQ00-1260B_670.g2.JPGROM 57723 (Fig. 8C) – OdontogriphusWQ99-0699A ROM 57723_639g gm 638.JPGROM 57723 (Fig. 8C, enlargement) – Odontogriphus foot, showing transverse linesWQ99-0699A ROM 57723_641.g.JPGROM 57725 (Fig. 8D) – OdontogriphusWQ95-1050A_174+175col.JPGROM 57725 (Fig. 8D) – Odontogriphus, lit to emphasize longitudinal lineations in medial regionROM 57725_175.g.JPG