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Fig. 8. Recent crustacean Euphausia superba Dana, 1852 in Soft-part preservation in two species of the arthropod Isoxys from the middle Cambrian Burgess Shale of British Columbia, Canada

Fig. 8. Recent crustacean Euphausia superba Dana, 1852 (krill) from Gerlache Strait, Antarctica. A. Left lateral view. B. Dorsal view. C. Detail of stalked eyes after removing head shield. All light micrographs.

Fig. 9 in Soft-part preservation in two species of the arthropod Isoxys from the middle Cambrian Burgess Shale of British Columbia, Canada

Fig. 9. Spiny shields in Recent crustaceans. A. Gnathophausia zoea Willemoes−Suhm 1873 (Malacostraca, Lophogastrida). B. Porcellanid larva (Decapoda). A from http://en.wikipedia.org/wiki/Crustacean; B from www.zooplankton−online.net/gallery.html (courtesy of W.S. Johnson, Goucher College); both used with permission of the copyright holders.

Fig. 5 in Soft-part preservation in two species of the arthropod Isoxys from the middle Cambrian Burgess Shale of British Columbia, Canada

Fig. 5. Bivalved arthropod Isoxys acutangulus (Walcott, 1908), Burgess Shale Formation, middle Cambrian, near Field, British Columbia, Canada (see Fig. 1), general morphology. A. ROM 57902A, headshield in dorsal view without soft parts, note the different angle of the contact between the pleural folds and the cardinal spines, which allows for the position of the stalked eyes. B. ROM 57907A, B; B1, part of unique specimen from WS locality, with eyes, telson and telson flaps; B2, counterpart; B3, line drawing of specimen. C. ROM 57904A; C1, specimen showing paired midgut glands and telson flaps; C2, line drawing of specimen. All dorsoventrally compressed specimens and photographed under polarized light; B2, in water. Midgut glands in gray tone.

Fig. 6 in Soft-part preservation in two species of the arthropod Isoxys from the middle Cambrian Burgess Shale of British Columbia, Canada

Fig. 6. Reconstruction of the bivalved arthropod Isoxys acutangulus (Walcott, 1908), swimming in the water column. Note that the position of the mouth and the attachments of the appendages to the body are conjectural. Not to scale.

Fig. 7. Bivalved arthropod Isoxys longissimus Simonetta and Delle Cave 1975 in Soft-part preservation in two species of the arthropod Isoxys from the middle Cambrian Burgess Shale of British Columbia, Canada

Fig. 7. Bivalved arthropod Isoxys longissimus Simonetta and Delle Cave 1975. Burgess Shale Formation, middle Cambrian, near Field, British Columbia, Canada (see Fig. 1), general morphology. A. USNM 18170, holotype. B. ROM 57910A. C. ROM 57911A. D. ROM 57909A. E. ROM 57908A, B; E1, part of slightly oblique specimen with soft−body preservation, including large eye, telson and some possible exopods; E2, counterpart; E3, line drawing of specimen. F. ROM 57919A. All laterally compressed specimens. A, low angle light from top left; B–F, polarized light.

Fig. 3 in Soft-part preservation in two species of the arthropod Isoxys from the middle Cambrian Burgess Shale of British Columbia, Canada

Fig. 3. Bivalved arthropod Isoxys acutangulus (Walcott, 1908), Raymond Quarry Shale Member, Burgess Shale Formation, middle Cambrian, near Field, British Columbia, Canada (see Fig. 1), general morphology. A. ROM 57898A; A1, specimen showing large stalked eyes and the pair of raptorial frontal appendages; A2, line drawing of specimen. B. ROM 57914A; B1, partially decayed specimen with most of body and appendages rotated towards the front; B2, line drawing of specimen. C. ROM 57899A; C1, specimen with raptorial appendages oriented backwards and possible telson flaps; C2, line drawing of specimen. D. ROM 59871A; D1, considerably decayed specimen showing forward rotation of body and appendage remains; D2, line drawing of specimen. All laterally compressed specimens and polarized light. Midgut glands in gray tone.

Fig. 1. A in Soft-part preservation in two species of the arthropod Isoxys from the middle Cambrian Burgess Shale of British Columbia, Canada

Fig. 1. A. Topographic map of the Burgess Shale area near Field, British Columbia (Canada). The numbers indicate localities where specimens of Isoxys acutangulus (Walcott, 1908) and Isoxys longissimus Simonetta and Delle Cave, 1975 were collected by ROM parties. 1. West slope of Fossil Ridge: 1a, Greater Phyllopod bed, Walcott Quarry; 1b, Raymond Quarry; 1c, "persephone layer" (RQ +20 to +23); 1d, "Tuzoia layer" (TZ); 1e, Collins Quarry—"Ehmaniella Zone" (EZ) and "Upper Ehmaniella" (UE); 2, South face of Mt. Field; 3, North shoulder of Mt. Stephen (ESA, ESB); 4, S7 locality; 5, Mt. Stephen Collins Quarry (WS); 6, Mt. Stephen Trilobite Beds (ST); 7, Stanley Glacier. B. Stratigraphic section of the Burgess Shale and Stephen Formations (modified from Fletcher and Collins, 1998). Circles indicate the levels where specimens of Isoxys acutangulus (Walcott, 1908) and Isoxys longissimus Simonetta and Delle Cave, 1975 from the seven localities in A were collected.

Fig. 4 in Soft-part preservation in two species of the arthropod Isoxys from the middle Cambrian Burgess Shale of British Columbia, Canada

Fig. 4. Bivalved arthropod Isoxys acutangulus (Walcott, 1908), Raymond Quarry Shale Member, Burgess Shale Formation, middle Cambrian, near Field, British Columbia, Canada (see Fig. 1). A. ROM 57905A, B; A1, part of specimen alternating midgut glands, possibly due to compaction, and narrow doublure; A2, specimen under low angle light from top left; A3, counterpart of specimen under low angle light from top left; A4, line drawing of specimen. B. ROM 57906B; B1, specimen with raptorial appendage, and 8 sets of midgut glands; B2, image showing endopod and exopod details; B3, specimen under low angle light from top left; B4, line drawing of specimen. All laterally compressed specimens. A1, B1, B2, polarized light; B2, in water; A2, A3, and B3 dry. Midgut glands in gray tone.

Fig. 5 in Soft anatomy of the Early Cambrian arthropod Isoxys curvirostratus from the Chengjiang biota of South China with a discussion on the origination of great appendages

Fig. 5. An early arthropod reconstruction of Isoxys curvirostratus (Vannier and Chen, 2000). The animal was covered by the carapace. The trunk length, which consists of 14 somites varies from 2 to 3 cm in adults. Large stalked eyes and a pair of uniramous prehensile appendages (5 podomeres) bearing stout inner outgrowths protruded anteriorly. The following appendages are biramous and uniform—i.e., a slender endopod with many podomeres and an exopod fringed with many long lamellae.

Fig. 4 in Soft anatomy of the Early Cambrian arthropod Isoxys curvirostratus from the Chengjiang biota of South China with a discussion on the origination of great appendages

Fig. 4. An early arthropod Isoxys curvirostratus (Vannier and Chen, 2000) from the Lower Cambrian Chengjiang biota, South China. A. JS0008 from Jianshan section; A1, posterior part of an incomplete specimen showing the frontal appendage, exopod, endopod; A2, detailed view of the frontal appendage, showing five podomeres and tooth−like outgrowths; A3, detailed view of exopod and endopod, showing the gill lamellae of exopod and the podomeres of endopod; A4, detailed view of endopod, showing its podomeres. B. EJ0404 from Erjie section; B1, showing the location of the eye stalk, trunk, proximal part of appendages and the outline of endopod; B2, camera−lucida drawing of B1. Abbreviations: as, anterior spine; en, endopod; es, eye stalk; ex, exopod; f1–5, podomeres of the frontal appendage from the distal to proximal; fa, frontal appendage; gl, gill lamellae of exopod; lv, left valve; p1–5, podomeres of endopod from the distal to proximal; pr, proximal part of appendage; rv, right valve; st, striated ornament; ta, trunk appendage; ti, trunk inclusion; 1–7, numbered trunk appendage.

Fig. 3 in Soft anatomy of the Early Cambrian arthropod Isoxys curvirostratus from the Chengjiang biota of South China with a discussion on the origination of great appendages

Fig. 3. An early arthropod Isoxys curvirostratus (Vannier and Chen, 2000) from the Lower Cambrian Chengjiang biota, South China. A. JS0014 from Jianshan section; A1, specimen showing the striated ornament of the carapace, eye, frontal appendages, exopod and trace of the trunk; A2, detailed view of eye sphere, showing two individual layers, the light external cornea and the dark internal core; A3, camera−lucida drawing of A1; A4, detailed view of frontal appendages, showing the intersegmental membranes, five podomeres and tooth−like outgrowths; A5, the counterpart of JS0014, showing the posterior part of specimen. B. EJ0417 from Erjie section, dorsal view showing the single shield carapace and unsplit base of anterior or posterior spines. Abbreviations: as, anterior spine; co, cornea; ex, exopod; f1–5, podomeres of the frontal appendage from the distal to proximal; fa, frontal appendage; ou, tooth−like outgrowth of the frontal appendage; ps, posterior spine; ru, retinular units; st, striated ornament.

Fig. 1 in Soft anatomy of the Early Cambrian arthropod Isoxys curvirostratus from the Chengjiang biota of South China with a discussion on the origination of great appendages

Fig. 1. An early arthropod Isoxys curvirostratus (Vannier and Chen, 2000) from the Lower Cambrian Chengjiang biota, South China. A. JS0010 from Jianshan section; A1, showing the outline and the striated ornament of the carapace; A2, detailed view of exopod, showing the gill lamellae; A3, camera−lucida drawing of A1; A4, detailed view of vascular integumental network. B. JS172 from Jianshan section; B1, detailed view of exopod, showing the gill lamellae; B2, showing the striated ornament on the posterior of the carapace and exopod. Abbreviations: as, anterior spine; ex, exopod; fa, frontal appendage; ps, posterior spine; rv, right valve; st, striated ornament; ta, trunk appendage; vn, vascular integumental network.

Fig. 2 in Soft anatomy of the Early Cambrian arthropod Isoxys curvirostratus from the Chengjiang biota of South China with a discussion on the origination of great appendages

Fig. 2. An early arthropod Isoxys curvirostratus (Vannier and Chen, 2000) from the Lower Cambrian Chengjiang biota, South China from Erjie section (A–C, E) and from Jianshan section (D). A. EJ0423; A1, complete specimen showing the outline of carapace, lamellae of the exopod; A2, camera−lucida drawing of A1. B. EJ0424, showing the eye spheres, frontal appendage, trunk and the traces of trunk appendages. C. EJ0422, immature specimen showing 14 trunk somites. D. JS154; D1, showing eye spheres, the number of the trunk somites and location of appendages; D2, camera−lucida drawing of D1. E. EJ0407; E1, showing the eye sphere and stalk, appendages in relief and the trunk; E2, camera−lucida drawing of E1. Abbreviations: es, eye stalk; ex, exopod; fa, frontal appendage; gl, gill lamellae of exopod; le, lateral eye; pr, proximal part of appendage; ps, posterior spine; te, telson; ti, trunk inclusion; 1–14, numbered trunk appendage.