Melchin et al.—Llandovery retiolitine graptolites from Arctic Canada
(15.7–12.4mm in 10 mm). Prosicula 0.25–0.35mm long with longitudinal rods (Fig. 13.2), virgella 0.38mm (one specimen). Ancora umbrella relatively shallow (below sicular aperture, accounting for compression), with two to three whorls of spiral lists, ~0.85mm wide across umbrella rim (Fig. 13.3). Rectangular ventral orifices on both walls. Thecal apertural lists horizontal, looping, alternating in position on opposite ventral walls in distinct, ladder-like succession. Zigzag list on reverse side, joining lateral apertural rods. Obverse side with only horizontal lateral apertural rods and vertical pleural lists. List micro-ornament of very fine, parallel striae (Fig. 13.4).
Etymology.—spirifer: L., spire-bearing; referring to the spiral lists that make up the ancora umbrella.
Remarks.—The very strong similarities of specimens of E. singularis and E. spirifer in terms of the structure of their thecal framework strongly suggest that they are congeneric. In comparing their morphometrics, however, they are quite different: E. singularis, which is earliest Telychian in age (S. guerichi Zone), is recorded by Sennikov (1984) as 1.8mm wide measured between the pleural lists, but ~2.5mm inclusive of the apertural lists, whereas our specimens of E. spirifer measure a maximum of only 1.6mm, including looping apertural lips. In addition, the Siberian material has a thecal spacing of 12–11 in 10mm (=2TRD 1.65–1.8 mm), whereas specimens of E. spirifer has much more closely spaced thecae (2TRD 1.28–1.68mm, or ~15.7–12 in 10 mm). The absence of a complete ancora umbrella in the Altai material prevents further comparisons between the two geographically and temporally separated collections.
Genus Aeroretiolites new genus
Type species.—Aeroretiolites cancellatus n. sp. (=‘Rotaretiolites’ sp. of Lenz and Melchin, 1997).
Other species.—Possibly Aeroretiolites? sp.
Diagnosis.—Ancora umbrella comprises radial lists with a continuous undulating rim with up to three whorls of spiral lists. Thecae with everted to horizontal apertural loops supported by slightly convex mid-ventral lists. Pleural lists present, joined to lateral apertural rods. Lists bear weak, parallel striations. Ancora sleeve weakly developed.
Etymology.—Aero: L, wicker basket; referring to the basket-like ancora umbrella.
139
Remarks.—Specimens of Aeroretiolites possess attributes of species of both Pseudoretiolites and Rotaretiolites. Like the former they possesses a bowl-like ancora umbrella with spiral lists (generally markedly smaller than those of Pseudoretiolites), and a micro-ornament of very fine striae, unlike the relatively coarse parallel ridges seen in specimens of Rotaretiolites. Like Rotaretiolites, each theca is floored by a single, simple, slightly convex mid-ventral list that meets a looping apertural lip.
Aeroretiolites cancellatus new species Figure 14.1–14.5, 14.9
1997 ‘Rotaretiolites’ Lenz and Melchin, fig. 2b.
Holotype.—Holotype GSC137651, fromthe L. convolutus Zone, Cape Manning, Cornwallis Island. Paratypes GSC137652-137654.
Diagnosis.—Ancora umbrella moderately shallow with two to three whorls of spiral lists. Prosicula normally preserved. Nema attached to transverse rods by connecting rods. Thecae comprise everted to horizontal apertural loops connected to mid-ventral lists. Mid-ventral lists slightly convex outward and inclined. Pleural lists present, vertical to slightly inclined and joined to lateral apertural rods. Lists bear weak, parallel striations. Reti- culum of ancora sleeve limited in development, with very coarse meshes on both lateral walls.
Materials.—14 specimens; two are complete, several have a well-preserved ancora umbrella, and others in which the distal portion remains, but are without the ancora umbrella.
Occurrence.—L. convolutus Zone, Cape Manning, Cornwallis Island, and Dundas Island.
Description.—Tubarium gradually widening proximally and
becoming parallel-sided, at least 5.8mm long, width across first thecal pair 1.0–1.1mm and 1.8–2.15mm distally. 2TRD 1.25–1.6mm (16–12.5 in 10mm) proximally, and 1.3–1.6mm distally (two specimens). Prosicula 0.35 long, virgella 0.40–0.45mm, with longitudinal rods. Ancora umbrella moder- ately shallow, reaching a level just below the aperture of the prosicula, bowl-shaped, with two or three whorls of spiral lists, width 0.8–0.9mm. A large ovate lateral orifice on each wall. Thecal apertural lips comprise everted to horizontal, looping lists, attached to slightly convexmid-ventral lists inclined to nema 30o–45o. Mid-ventral list of theca 11 connected to rim of ancora umbrella. Lateral aperture rods curved, pleural lists vertical to variably, slightly inclined. Zigzag lists on reverse side, nema
Figure 14. Scanning electron microscopy images of Aeroretiolites cancellatus n. gen. n. sp. and Aeroretiolites?sp. (1–5, 9) Aeroretiolites cancellatus n. gen. n. sp.: (1, 3, 4) holotype GSC137651, (1) stereopair of well-preserved specimen with three thecal pairs and ancora umbrella with three spiral whorls, prosicula, attachment of nema to connecting rods (a), and attachment of base of mid-ventral list of theca 11 (b) to ancora umbrella rim, (3) proximo-lateral view of ancora umbrella and prosicula, (4) sicula, showing fine longitudinal rods, note also smooth to finely striated list surfaces, section MCM88-10, 6.5, L. convolutus Zone; (2) paratype GSC137652, stereopair of ventrally flattened specimen with two whorls of spiral lists on ancora umbrella and large lateral orifice; (5) paratype GSC137653, stereopair of distal portion of mature specimen with seven thecal pairs, moderate ancora sleeve, showing sloping pleural lists (a), lateral apertural rods (b), mid-ventral lists (c), section MCM2-98, 54.0–54.15, L. convolutus Zone; (9) paratype GSC137654, distal specimen of tubarium, with four thecal pairs and ancora sleeve, section MCM2-98, 54.0–54.15, L. convolutus Zone. (6–8) Aeroretiolites? sp.: GSC137655, (6) stereopair of very well preserved, complete specimen with five pairs of thecae, a shallow ancora umbrella without spiral lists, and parallel and continuously connected pleural lists, (7) enlargement of list surfaces showing smooth to finely striated microstructure, (8) oblique proximal view showing simple ancora structure, sectionMCM2-98, 54.0-54.15, L. convolutus Zone.
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180 |
Page 181 |
Page 182 |
Page 183 |
Page 184 |
Page 185 |
Page 186 |
Page 187 |
Page 188 |
Page 189 |
Page 190 |
Page 191 |
Page 192 |
Page 193 |
Page 194 |
Page 195 |
Page 196 |
Page 197 |
Page 198 |
Page 199 |
Page 200 |
Page 201 |
Page 202 |
Page 203 |
Page 204 |
Page 205 |
Page 206 |
Page 207 |
Page 208
