Nectocaridids are soft-bodied early to middle Cambrian organisms known from Burgess Shale-type deposits in Canada, China, and Australia. Originally described as unrelated species, they have recently been interpreted as a clade; their flexible tentacles, camera-type eyes, lateral fins, internal gills, axial cavity, and funnel point to a relationship with the cephalopods. However, aspects of this reinterpretation, including the relevance of the group to cephalopod evolution, have been called into question. Here, I examine new and existing nectocaridid material, including a large new form that may represent a sexual dimorph of Nectocaris pteryx. Differences between existing taxa largely represent taphonomic variation between sites and specimens—which provides further constraint on the organisms' anatomy. I revise the morphology of the tentacles and fins, and describe mouthparts and phosphatized gills for the first time. A mathematical analysis supports the presence of the earliest known camera-type eyes, and fluid mechanical considerations suggest that the funnel is optimized for efficient jet propulsion in a low Reynolds number flow regime. Nectocaridids closely resemble coleoid cephalopods, but a position deeper within Cephalopoda raises fewer stratigraphic challenges. Whether its coleoid-like construction reflects common ancestry or profound convergence, the Nectocaris body plan adds substantially to Cambrian disparity, demonstrating the rapid colonization of nektobenthic niches after the Cambrian explosion.
Fig. 1a: ROM 59658 – Nectocaris pteryx from the Burgess Shale
External body tissue is intact, obscuring internal structures
RQ93-0376_338.g1.JPG
Fig. 1b: ROM 49585 – Nectocaris pteryx from the Burgess Shale
Slight decay reveals internal anatomy but not fin structure
UE88-0106A_071.g.JPG
Fig. 1c: ROM 59660 – Nectocaris pteryx from the Burgess Shale
Moderate decay reveals internal anatomy and fin structure
UE88-0012A_067.g2.JPG
Fig. 1d: ROM 60089 – Nectocaris pteryx from the Burgess Shale
Decayed specimen, many organs are visible but no detail is preserved
EZ88-0174A_513.g.JPG
Fig. 1e: ROM 60133 – Nectocaris pteryx from the Burgess Shale
Heavily decayed specimen, no detail visible.
RQ91-0892A_058.g.JPG
Fig. 2a: Elemental distribution in Nectocaris pteryx, ROM 60079
Pixel brightness in elemental maps corresponds to elemental abundance. Scale bars: 1 mm.
WT98-1378B Elemental.png
Figs. 2b & 9e: ROM 60079 – Nectocaris pteryx from the Burgess Shale
WT98-1378B.png
Figs. 2c, 6b & 8b: ROM 60146 — Nectocaris pteryx (head) from the Burgess Shale, direct illumination
Specimen with well-preserved soft tissue has smooth, unornamented tentacle margins. Robustly lined funnel canal is surrounded by fleshy tissue.
BW97-2549A_708.JPG
Figs. 2c, 6b & 8b: ROM 60146 — Nectocaris pteryx (head) from the Burgess Shale, crossed polars
Specimen with well-preserved soft tissue has smooth, unornamented tentacle margins. Robustly lined funnel canal is surrounded by fleshy tissue.
BW97-2549A_709.JPG
Figs. 2c, 6b & 8b: ROM 60146 — Nectocaris pteryx (head) from the Burgess Shale, interference image
Interference image, using images under direct illumination and crossed polars. Specimen with well-preserved soft tissue has smooth, unornamented tentacle margins. Robustly lined funnel canal is surrounded by fleshy tissue.
BW97-2549A_709 gex 708.bw.jpg
Fig 2d: ROM 60146 — Elemental distribution in eye and head of Nectocaris pteryx from the Burgess Shale
ROM 60146 Elemental.png
Fig. 3a: Bioturbation in Nectocaris ?pteryx from Chengjiang
HKMF-50001
Petalilium_HK-MF-00001A_098.g2.JPG
Fig. 3b: Bioturbation in Nectocaris ?pteryx from Chengjiang
HKMF-50001 — Magnification of head region
Petalilium_HK-MF-00001A_114.g2.JPG
Bioturbation in Nectocaris pteryx from the Burgess Shale
ROM 60117, Burgess Shale specimen with minimal burrowing, infill of axial cavity undisturbed
UE90-1114A_257.g.JPG
Bioturbation in Nectocaris ?pteryx from Chengjiang
HK-MF-00002, Chengjiang specimen; axial cavity decimated by burrowing.
Petalilium_HK-MF-00002A_091.g1.JPG
Figs. 4a & 9a: ROM 59658 – Nectocaris pteryx from the Burgess Shale
ROM 59658, composite interference image of part and counterpart, showing coarse stripes, fine striations, and folding of fin margin
RQ93-0322 AB overlay.bw.jpg
Fig. 4a: ROM 59658 – Nectocaris pteryx from the Burgess Shale
Part, under crossed polars
RQ93-0322B_714.g.tif
Fig. 4a: ROM 59658 – Nectocaris pteryx from the Burgess Shale
Part, direct illumination
RQ93-0322B_713.g.tif
Fig. 4a: ROM 59658 – Nectocaris pteryx from the Burgess Shale
Counterpart, crossed polars
RQ93-0322A_710.g.tif
Fig. 4a: ROM 59658 – Nectocaris pteryx from the Burgess Shale
Counterpart, direct illumination
RQ93-0322A_711.g.tif
Fig. 4b: ROM 60079 – Nectocaris pteryx from the Burgess Shale
ROM 60079, composite interference image of part and counterpart, showing coarse stripes and fine striations
WT98-1378 AB multiply.JPG.jpg
Fig. 4b: ROM 60079 – Nectocaris pteryx from the Burgess Shale
Counterpart, crossed polars
WT98-1378B_705.g1.JPG
Fig. 4b: ROM 60079 – Nectocaris pteryx from the Burgess Shale
Counterpart, direct illumination
WT98-1378B_703.g.JPG
Fig. 4b: ROM 60079 – Nectocaris pteryx from the Burgess Shale
Part, direct illumination
WT98-1378B_700.g.tif
Fig. 4b: ROM 60079 – Nectocaris pteryx from the Burgess Shale
Part, crossed polars
WT98-1378B_699.g.tif
Fig. 4b: ROM 60079 – Nectocaris pteryx from the Burgess Shale
Part, interference image of crossed polars and direct illumination
WT98-1378B_699 gx 700.JPG
Figs. 4c & 10c: ROM 60144 – Nectocaris pteryx from the Burgess Shale
Complementary preservation of lineations: broad stripes are visible anteriad, fine striations posteriad. Assuming that this represents a single individual, the anterior portion of this specimen is somewhat oblique to the sediment. Interference image.
WT94-0628A ROM 60144_370g gex 371g.g.JPG
Figs. 4c & 10c: ROM 60144 – Nectocaris pteryx from the Burgess Shale
Crossed polars
WT94-0628A ROM 60144_370.g.JPG
Figs. 4c & 10c: ROM 60144 – Nectocaris pteryx from the Burgess Shale
Direct illumination
WT94-0628A ROM 60144_371.g.JPG
Fig. 4d: ROM 60091 – Nectocaris pteryx from the Burgess Shale
Fine striations associated with relief, stripes not visible
UE88-0133B_377.g.JPG
Fig. 4d: ROM 60091 – Nectocaris pteryx from the Burgess Shale
Complete specimen; low angle light
UE88-0133B_114.g.tif
Fig. 4d: ROM 60091 – Nectocaris pteryx from the Burgess Shale
Full specimen, crossed polars
UE88-0133B_113.g.tif
Fig. 4e: ROM 60141 – Nectocaris pteryx from the Burgess Shale
Fine striations have distinct composition, stripes not visible
RQ93-1088B_110.g.JPG
Fig. 5a: ROM 60084 — Nectocaris pteryx from the Burgess Shale
ROM 60084, stain lines axial cavity
EZ88-0021A_118.g3.JPG
Fig. 5c: ROM 59661 — Nectocaris pteryx (lateral view) from the Burgess Shale
Part, lateral specimen with staining in axial canal
UE90-1394IA_127.g.JPG
Fig. 5c: ROM 59661 — Nectocaris pteryx (lateral view) from the Burgess Shale
Counterpart
UE90-1394IB_315.g.JPG
Fig. 6a: ROM 59660 – Nectocaris pteryx (anterior) from the Burgess Shale
Iterated transverse stripes with diffuse margins in twisted, partly decayed tentacle
UE88-0012A_079.g.JPG
Fig. 6b: ROM 60146 – Nectocaris pteryx (head) from the Burgess Shale
Specimen with well-preserved soft tissue has smooth, unornamented tentacle margins; interference image under plane and crossed polars.
BW97-2549A_709 gex 708.JPG
Tentacle curvature in Nectocaris pteryx from the Burgess Shale
Left tentacle demonstrates flexible curvature
UE88-0052B.g.jpg
Tentacle flexibility in Nectocaris pteryx from the Burgess Shale
Right tentacle (arrowed) is folded back over body
RQ96-0371A_136.png
Fig. 7a: ROM 59668 — Nectocaris pteryx mouthparts from the Burgess Shale
ROM 59668, denticles associated with relief
UE88-0015A_439.g.JPG
Fig. 7b: ROM 59662 — Nectocaris pteryx mouthparts from the Burgess Shale
Two opposed chevrons forming a cross
EZ84-0561A_507.g.JPG
Fig. 7c: ROM 60100 — Nectocaris pteryx (head) from the Burgess Shale
denticles of posterior chevron demonstrate relief; anterior chevron putatively represented by crack
UE90-0502B ROM 60100_412.g.JPG
Fig. 7c: ROM 60100 — Nectocaris pteryx mouthparts from the Burgess Shale
Direct illumination
UE90-0502B_177.g3.JPG
Fig. 7c: ROM 60100 — Nectocaris pteryx mouthparts from the Burgess Shale
Low-angle light, emphasizing relief
UE90-0502B ROM 60100_412.g.JPG
Fig. 7d: ROM 59661 — Nectocaris pteryx head (lateral view) from the Burgess Shale
Lateral specimen illustrating curved belt-like structure with serially repeated linear notches projecting radially.
UE90-1394A_115.g.JPG
Fig. 8a: ROM 60129 – Nectocaris pteryx from the Burgess Shale
Canal has robust dark lining, lateral voids visible in axial cavity
UE90-1439A_304.g.JPG
Fig. 8c: ROM 59662 – Nectocaris pteryx from the Burgess Shale
Canal narrows within the internal portion of the funnel.
UE90-0561_087.g.JPG
Fig. 9b: ROM 59664 – Nectocaris pteryx from the Burgess Shale
Gill laminae distend from zig-zagging lateral axis
UE90-1348A_327.g.JPG
Fig. 9c: ROM 59672 – Nectocaris pteryx from the Burgess Shale
Dark components of gills have thick edges, suggesting a cylindrical profile
UE90-1395a_492.g.JPG
Fig. 9d: ROM 60132 – Nectocaris pteryx from the Burgess Shale
Gill blades are laterally connected
UE90-1498_324.g.JPG
Fig. 9f: ROM 59663 – Nectocaris pteryx from the Burgess Shale
Sediment interdigitates between gill blades; blades are deflected posteriad
UE90-0414A_135.g.JPG
Fig. 9g: ROM 59656 – Nectocaris pteryx from the Burgess Shale
Anterior gill blades deflected backwards by interdigitating sediment; undeformed posterior blades canalize the sediment
EZ84-0668B_343.g.JPG
Fig. 10a: ROM 59659 – Nectocaris pteryx from the Burgess Shale
Bars preserved as dark two-dimensional regions lateral to the gills.
UE88-0007B_055.g.JPG
Fig. 10b: ROM 59664 – Nectocaris pteryx from the Burgess Shale
Bars preserved as dark two-dimensional regions, not in phase with gill blades.
UE90-1348B_043.g.JPG
Fig. 10d: ROM 60131 – Nectocaris pteryx from the Burgess Shale
Low angle lighting highlights irregular fracture pattern between bars and flat surfaces of fins.
UE90-1450A_034.g.JPG
Fig. 10e: ROM 60088 – Nectocaris pteryx from the Burgess Shale
Pale white sheath surrounds bars
UE88-0126_050.g.JPG
Fig. 10f: ROM 59670 – Nectocaris pteryx from the Burgess Shale
Distinct colouration in lateral body
UE88-0052a_006.g2.JPG
Fig. 10g: ROM 59656 – Nectocaris pteryx from the Burgess Shale
Complete specimen
EZ84-0688A_349.g.JPG
Fig. 10g: ROM 59656 – Nectocaris pteryx from the Burgess Shale
Posterior region. Stripes represent a taphonomic feature produced by the bars
EZ84-0688A_354.g2.JPG
Fig. 10i: Reconstruction of nectocaridid internal anatomy
Model showing relationship between bars (brown, interpreted as being associated with muscle), gills (mauve), fins (cream), and axial cavity (blue). Model generated in Blender.
Reconstruction_16-out.jpg
Fig. 10i: Reconstruction of nectocaridid internal anatomy (3D model)
3D model used to generate Fig. 10i. Blender file format.
Nectocaris interior schematic.blend
Fig. 11a: HK-MF-00002 — Nectocaris ?pteryx, large morph from Chengjiang
Infill of funnel canal appears braided; axial cavity reworked by burrowing
Petalilium_HK-MF-00002A_091.JPG
Fig. 11a: HK-MF-00002 (head) — Nectocaris ?pteryx, large morph from Chengjiang
Denticulate chevron structure between tentacles; planar lateral surface of eye
Petalilium_HK-MF-00002A_063.g.JPG
Fig. 11a: HK-MF-00002 (posterior) — Nectocaris ?pteryx, large morph from Chengjiang
Dark posterior structure
Petalilium_HK-MF-00002A_076.g.JPG
Fig. 11b: HK-MF-00001 — Nectocaris ?pteryx, large morph from Chengjiang
Showing striated funnel infill, pervasive bioturbation in axial cavity, projections from head, relief associated with fin striations, and bars with ?shrinkage-related wrinkling
Petalilium_HK-MF-00001A_114.g.JPG
Fig. 11b: HK-MF-00001 (anterior) — Nectocaris ?pteryx, large morph from Chengjiang
Showing striated funnel infill, pervasive bioturbation in axial cavity, and projections from head
Petalilium_HK-MF-00001A_155.g.JPG
Fig. 11b: HK-MF-00001 (fin) — Nectocaris ?pteryx, large morph from Chengjiang
Showing relief associated with fin striations, and bars with ?shrinkage-related wrinkling
Petalilium_HK-MF-00001A_127.g.JPG
Fig. 11c: SK-Z-00001 — Nectocaris ?pteryx, large morph from Chengjiang
Long tentacles, funnel folded laterally; bars and texture of infilling sediment apparent
Petalilium_SK-Z-00001_007.g2.JPG
Fig. 11c: ANSK-20001 — Nectocaris ?pteryx, large morph from Chengjiang
ANSK-20001 (=SK-Z-00001), long tentacles, funnel folded laterally; bars and texture of infilling sediment apparent
Petalilium_SK-Z-00001_007.g6.jpg
Fig. 11c: ANSK-20001 — Nectocaris ?pteryx, large morph from Chengjiang
Low angle lighting to accentuate relief. Illuminated from top left when anterior of specimen is at bottom of page.
Petalilium_SK-Z-00001_045.g2.JPG
Fig. 11c: ANSK-20001 — Nectocaris ?pteryx (anterior), large morph from Chengjiang
Magnification of anterior region of specimen
Petalilium_SK-Z-00001_019.g.jpg
Additional Chinese material of Nectocaris ?pteryx (large morph)
ZIP file containing images of two specimens, with scales
China_Nectocaris.zip
Fig. 11d: ROM 61496 — Large morph of Nectocaris from the Burgess Shale
Full size, high-resolution images as displayed in Fig. 11d, plus original (pre-interference) images.
Fig 11d - WQ94-3486.zip
Counterpart of ROM 61496 — Large morph of Nectocaris from the Burgess Shale
Images of the counterpart of ROM 61496; one (_271) under cross polars, the other (_265) in low angle light to highlight relief.
WQ94-3486_counterpart.zip
Large and small morphs of Nectocaris, to scale (reconstruction)
A reconstruction of the large and small morphs of Nectocaris, to scale, constructed in Blender, using fossil material to constrain shape and proportions.
Nectocaris reconstruction.jpg
3D model of Nectocaris (large and small morphs)
A Blender model of the large and small morphs of Nectocaris, to scale, constructed in Blender, using fossil material to constrain shape and proportions.
Nectocaris reconstruction.blend