Xystoscolex boreogyrus, Morris & Peel, 2010

Morris, Simon Conway & Peel, John S., 2010, New palaeoscolecidan worms from the Lower Cambrian: Sirius Passet, Latham Shale and Kinzers Shale, Acta Palaeontologica Polonica 55 (1), pp. 141-156 : 154

Xystoscolex boreogyrus sp. nov.

Figs. 3 , 4A, C–F , 5 , 6A, E .

Etymology: From the Greek words boreas (northern) and gyros (ring), a reference to both the prominent tubercles encircling the posterior trunk and also the midnight sun encircling the Arctic skies.

Holotype: MGUH 29144 ( Figs. 3C , 6E ).

Type locality: Peary Land, central North Greenland, situated at the south−western end of the broad valley (Sirius Passet) that connects J.P. Koch Fjord and Brainard Sund; latitude 82 ° 47.6’N, longitude 42 ° 13.3’W, altitude 450 m above sea level .

Type horizon: Lower part of the Buen Formation (lower Cambrian, provisional Series 2, Stage 3), equivalent to the Nevadella Zone of North American usage.

Material.— The holotype and MGUH 29142–29147 , 29149 , 29150 , 29152 .

Diagnosis.—As for Chalozoscolex, but introvert with anterior spines. Trunk ornamentation substantially more subdued and posterior trunk with larger number of tuberculate segments encircling body.

Stratigraphic and geographic range.—Buen Formation (Stage 3 of provisional Cambrian Series 2, equivalent to Nevadella Zone ), Peary Land (North Greenland).

Figures

Fig. 3. Palaeoscolecidan Xystoscolex boreogyrus gen. et sp. nov., lower Cambrian (Series 2, stage 3), Buen Formation, Sirius Passet Fossil−Lagerstätte, Peary Land, North Greenland. A. MGUH 29142, entire specimen with introvert at top right; note also gut trace. B. MGUH 29143, entire specimen (B1) and enlargement of posterior (upper) and introvert with anterior spines (B2). C. MGUH 29144, detail of introvert (C1) and entire specimen (C2); see also Fig. 6E. D. MGUH 29145, detail of introvert (upper) and posterior termination (lower right) (D1) and entire specimen (D2). E. MGUH 29146, entire specimen. Scale bars 10 mm. All specimens coated with sublimate.

Fig. 4. Palaeoscolecidans Xystoscolex boreogyrus gen. et sp. nov. (A, C–F) and Chalazoscolex pharkus gen. et sp. nov. (B, G), lower Cambrian (Series 2, stage 3), Buen Formation, Sirius Fossil−Passet Lagerstätte, Peary Land, North Greenland. A. MGUH 29147, anterior with introvert. B. MGUH 29148, enlargement of introvert and anterior trunk (B1) and entire specimen with gut trace (B2); see also Fig. 6F. C. MGUH 29149, enlargement of posterior end (C1) and entire specimen with gut trace (C2). D. MGUH 29142, enlargement of introvert, see also Fig. 3A. E. MGUH 29150, entire specimen (E1) and enlargement of introvert with everted pharyngeal region (E2); see also Fig. 6A. F. MGUH 29151, gut trace containing arthropod Isoxys volucris Williams, Siveter, and Peel, 1996 with characteristic spinose extension arrowed. G. MGUH 29137, gut trace; see also Fig. 2C. Scale bars 5 mm in D, G; otherwise 10 mm. All specimens coated with sublimate.

Fig. 5. Palaeoscolecidan Xystoscolex boreogyrus gen. et sp. nov., lower Cambrian (Series 2, stage 3), Buen Formation, Sirius Passet Fossil−Lagerstätte, Peary Land, North Greenland. MGUH 29152. A. Anterior and posterior (upper left) ends of folded specimen. B. Detail of introvert with anterior scalids and in lower right sclerites of posterior (lower left). Scale bars 10 mm. Specimen coated with sublimate.

Fig. 6. Scanning electron micrographs of Xystoscolex boreogyrus gen. et sp. nov (A, E) and Chalazoscolex pharkus gen. et sp. nov (B–D, F), lower Cambrian (Series 2, Stage 3), Buen Formation, Sirius Passet Fossil−Lagerstätte, Peary Land, North Greenland. A. MGUH 291560, scalids of the introvert, see also Fig. 4E. B. MGUH 29133, grooves and ridges on the introvert, see also Fig. 1A. C. MGUH 29136, segments of trunk showing longitudinal cuticular ridges, see also Fig. 2B. D. MGUH 29141, posterior trunk with larger sclerites, see also Fig. 2G. E. MGUH 29144, detail of scalid, distal point to upper right, see also Fig. 3C. F. MGUH 29148, segments with rows of sclerites and intervening unarmoured areas of cuticle (F1) and scalids of introvert (F2), see also Fig. 4B. Scale bars 400 µm (A+F1), otherwise 300 µm. All specimens coated with gold film.