Camptonectes (Costicamptonectes) milnelandensis Fursich 1982

• Main Authors: Hryniewicz, Krzysztof, Little, Crispin T. S., Nakrem, Hans Arne
• Format: Text
• Language: unknown
• Published: Zenodo 2014
• Subjects: Biodiversity; Taxonomy; Animalia; Mollusca; Bivalvia; Pectinoida; Pectinidae; Camptonectes; Camptonectes milnelandensis; British Columbia; Canada; Fulcrum; Greenland; Milne Land; Slottsmøya; Svalbard; East Greenland; Spitsbergen
• Online Access: https://dx.doi.org/10.5281/zenodo.5228250; https://zenodo.org/record/5228250

Camptonectes ( Costicamptonectes ) aff. milnelandensis Fürsich, 1982 (Figure 10 H–K) 1982 aff. Camptonectes ( Costicamptonectes ) milnelandensis sp. nov. —Fürsich, p. 50, figs. 23 C–D, F, G. Material examined. Two poorly preserved right valves. In addition a single external mould with silicone rubber cast from the Dorsoplanites bed (PMO 226.604). See Appendix 1 for the list of specimens. Dimensions. 15–30.5 mm in length, 15–28.2 mm in height. See Appendix 2G for details. Description. Shell small to medium sized, very thin, appears to get shorter at later growth stages. Right valve suborbicular, moderately inflated, with small posterior and larger anterior auricle, ventrally delineated by a deep byssal notch. Ctenolium well developed. Antero- and posterodorsal margins subequal, anterodorsal margin slightly concave. Anterior margin slightly more convex than posterior margin, ventral margin evenly rounded. Preserved ornament consists of weak divaricating radial ribs, intersected by weak but dense growth lines. Anterodorsal margin ornamented by ca. 6 subparallel radial ribs. Left valve, musculature and dentition unknown. Remarks. We compare our specimens with C . ( Co. ) milnelandensis because of its ornament of commarginal growth lines accompanied by divaricate ribs and with additional radial ribs close to the anterodorsal margin. The Svalbard specimens have a slightly higher umbonal angle than comparatively sized specimens of C . ( Co. ) milnelandensis from Greenland (Fürsich 1982). However, no specimens larger than 18 mm were reported by Fürsich (1982) so we are unable to compare the ontogenetic changes of umbonal angle of specimens from both localities. In addition, the Svalbard material is composed of right valves only. Until more is known about C . ( Co. ) milnelandensis from both Greenland and Svalbard, we prefer to leave our species in open nomenclature. Occurrence. Camptonectes ( Co. ) milnelandensis : Upper Callovian–Upper Oxfordian of Milne Land, East Greenland (Fürsich 1982). Camptonectes ( Co. ) aff. milnelandensis : Seep 8 (Upper Volgian), Slottsmøya Member (Tab. 1); also Dorsoplanites bed (Middle Volgian), Svalbard. Palaeoecology. We assume that C . ( Co. ) aff. milnelandensis was a byssally attached suspension feeder, as indicated by the presence of a well-developed ctenolium. Byssal attachment is a characteristic feature for the genus Camptonectes , although larger species in the subgenus McLearnia Crickmay, 1930, probably lost a functional byssal attachment in maturity (e.g. Fürsich 1982). An expanded anterior auricle in pectinids is an adaptation for byssal attachment with the commissure non-perpendicular to the substrate (Stanley 1970). In such a position the auricle and anterior shell margin acts as a fulcrum and prevents the shell overturning from its set position. As in most of the pectinids, C . ( Co. ) aff. milnelandensis probably had the ability to swim to escape predation, although the umbonal angle is too acute to assume this was habitual (Stanley 1970). : Published as part of Hryniewicz, Krzysztof, Little, Crispin T. S. & Nakrem, Hans Arne, 2014, Bivalves from the latest Jurassic-earliest Cretaceous hydrocarbon seep carbonates from central Spitsbergen, Svalbard, pp. 1-66 in Zootaxa 3859 (1) on page 27, DOI: 10.11646/zootaxa.3859.1.1, http://zenodo.org/record/4930112 : {"references": ["Fursich, F. T. (1982) Upper Jurassic bivalves from Milne Land, East Greenland. GrOnlands Geologiske UndersOgelse, 144, 1 - 126.", "Crickmay, C. H. (1930) Fossils from Harrison Lake area, British Columbia. Bulletin of the National Museum of Canada, 63, 33 - 66, pls. 1 - 15.", "Stanley, S. M. (1970) Relation of shell form to life habits of the Bivalvia (Mollusca). The Geological Society of America Memoir, 125, 1 - 296. http: // dx. doi. org / 10.1130 / mem 125 - p 1"]}