Sinuarbullina yangouensis (Pan, Erwin, Nutzel, & Xiang-Shui, 2003) comb. nov.

Foster, William J., Danise, Silvia & Twitchett, Richard J., 2017, A silicified Early Triassic marine assemblage from Svalbard, Journal of Systematic Palaeontology 15 (10), pp. 851-877 : 869

Sinuarbullina yangouensis (Pan, Erwin, Nutzel, & Xiang-Shui, 2003) comb. nov.

( Fig. 13 )

2003 Jiangxispira yangouensis Pan, Erwin, Nutzel, & Xiang-Shui : 44, fig. 3, 1–7.

Material. Specimen lost by WJF after photography.

Description. The shell is high-spired, slender and fusiform. Teleoconch whorls have a subsutural ramp. The ramp from the outer whorl face is rounded with a rib on the shell periphery. Whorls are smooth, except for growth lines which are prosocyrt on the outer whorl face curving in an apertural direction and become opisthocyrt towards the ramp. The surface of the shell shows a coloured spiral band around the subsutural ramp. The aperture is an elongated teardrop shape. Protoconch is heterostrophic, sinistral, nearly discoidal with lightly elevated spire 30 Ǫ offset from the shell axis; protoconch has 1–2 round whorls.

Remarks. Seven species are included in Sinuarbullina , and S. convexa (= ‘ Cylindrobullina’ convexa ) is the only accepted species from the Lower Triassic (Grundel & Nutzel 2012). These specimens are more slender than S. convexa , described from the Sinbad Limestone of the western USA by Batten & Stokes (1986), and better resemble Jiangxispira yangouensis from the Induan Dayie Formation, China.

The shell morphology is similar to that of Meekospira , which has been interpreted as a slow-moving shell dragger ( Hughes 1986), but could have also been a burrower ( Hollingworth & Pettigrew 1988). Interpreting the feeding strategy of fossil gastropods is difficult because information on the organ system, including the ctenidium, is not usually preserved. The ancestral ecology of high-spired gastropods is presumably as algal grazers on hard substrates ( Declerck 1995). Given the absence of hard substrates in this study, the specimens described herein were probably detritus feeders or possibly micro-carnivorous on sedentary prey, like many modern shelled opisthobranchs (e.g. Lobo da Cunha et al. 2009).

Mode of life. Surficial, fully motile, slow, deposit feeder.

Figures

Figure 13. Sinuarbullina yangouensis (Pan et al., 2003). A, B, lateral views; C, D, views of the protoconch. Scale bars = 1 mm, except D. Note: specimen lost by WJF after photography.