Clisospirinae Miller, 1889

Ebbestad, Jan Ove R. & Cope, John C. W., 2021, A low diversity Sinuites gastropod community from the Floian, Early Ordovician, of South Wales, Acta Palaeontologica Polonica 66 (2), pp. 319-335 : 324

Subfamily Clisospirinae Miller, 1889

Remarks.—Sinistrally coiled members of the Mimospirida Dzik, 1983 , are a small but conspicuous part of Ordovician mollusc communities (total range of the group is Cambrian– Devonian ( Frýda 2012)). Classification of these forms has been widely discussed, but currently they are considered as basal gastropods of uncertain systematic position (Fryda and Bouchet in Bouchet et al. 2005; Frýda 2012; Bouchet et al. 2017; Ebbestad et al. 2020a). The order contains two families within the superfamily Clisospiroidea Miller, 1889 , the Clisospiridae Miller, 1889 , and the Onychochilidae Koken in Koken and Perner, 1925. Members of the former are usually moderately high spired and have a wide open base (pseudoumbilicus) embraced by a frill or rib, while the members of the latter have broad and low shells with a funnel­like umbilicus ( Wängberg­Eriksson 1979; Dzik 1983).

In the Llangynog fauna the Clisospiridae are represented by a species of Mimospira Koken in Koken and Perner, 1925, a genus found mainly in Ordovician strata and only two records in the Silurian ( Peel 1975; Wängberg­Eriksson 1979). The Onychochilidae is represented by Catalanispira Ebbestad, Kolata, and Isakar, 2020a , as genus hitherto only known from one species in the Middle Ordovician (Dw3) of Estonia and one in the Upper Ordovician (Sa2) of the USA ( Ebbestad et al. 2020a). Both new records of Mimospira and Catalanispira in Wales are amongst the oldest of their genera.

Genus Mimospira Koken in Koken and Perner, 1925

Type species: Onychochilus helmhackeri Perner, 1900: 4 , 14, by subsequent designation of Knight (1937: 710), from the Arenigan (Darriwilian, Dw1, Middle Ordovician) upper pyroclastic member of the Klabava Formation near Kváň, Bohemia, Czech Republic.

Remarks.—Most species of Mimospira are small (height 5 mm or less) and many are left in open nomenclature. Ordovician Mimospira are known from at least nine species through the Ordovician of Baltoscandia and Poland ( Yochelson 1962, 1963; Wängberg­Eriksson 1979; Dzik 1983; Isakar and Peel 1997; Frýda and Rohr 1999; Frisk and Ebbestad 2007; Lindskog et al. 2015), one Tremadocian (Lower Ordovician) species in the Franconian Forest (Frankenwald) of Germany ( Sdzuy et al. 2001), one species from the Katian (Upper Ordovician) of the Carnic Alps in Austria ( Gubanov and Bogolepova 1999), six species from the Tremadocian–Katian of the Prague Basin, Czech Republic ( Frýda 1989; Frýda and Rohr 1999; Horný 1999; Kraft et al. 2013, 2015), one species from the Sandbian (Upper Ordovician) of Scotland ( Longstaff 1924; Frýda and Rohr 1999; Stewart 2012), two species from the Floian (Lower Ordovician) and Dapingian (Middle Ordovician) of Wales ( Bates 1963; this paper) and one Darriwilian (Middle Ordovician) species in the Precordillera of Argentina ( Dzik 2020), giving a total of at least 20 species.

Rohr (1996) reported M. aff. M. cochleata Lindström, 1884 , from the lower part of the Whiterockian (Dapingian, Dp1; Middle Ordovician) in the lower Antelope Valley at Meiklejohn Peak in Nevada, USA, which was compared to the Silurian species from Gotland, Sweden ( Lindström 1884; Wängberg­Eriksson 1979). The two are broadly similar in having a distinct rounded angular periphery low on the whorl, which is lacking in Ordovician species. They differ in the densely spaced oblique lirae in the Silurian form that cross the periphery without a change in direction, and the much sharper angulation of the periphery in the Nevada form. The latter shows widely spaced lirae that are prosocline on the upper whorl surface sweeping strongly backwards to the sharp periphery. Just below the periphery the lirae seem to curve more strongly abaperturally before sweeping evenly backwards, although the angulation may enhance this impression. Rohr (1996) compared the whorl profile of the Nevada form with that of the Late Ordovician species of Angulospira Wängberg­Eriksson, 1979 , from the Katian Boda Limestone of Sweden. The idea is followed up here, and is suggested that species of Angulospira as well as Bodaspira Wängberg­Eriksson, 1979, compare better with the Nevada form than species of Mimospira . Similarities between the Nevada form and Bodaspira undulata Wängberg­Eriksson, 1979 , in the peripheral angulation, distinction of the lirae and direction of these across the periphery is compelling and the Nevada species is therefore here transferred to Bodaspira sp.