Fluctuaria Muir-Wood and Cooper, 1960

Carniti, Alessandro P., Porta, Giovanna Della, Banks, Vanessa J., Stephenson, Michael H. & Angiolini, Lucia, 2022, Brachiopod fauna from uppermost Visean (Mississippian) mud mounds in Derbyshire, UK, Acta Palaeontologica Polonica 67 (4), pp. 865-915 : 895

Genus Fluctuaria Muir-Wood and Cooper, 1960

Type species: Productus undatus Defrance, 1826 , from the upper Vise- an of Visé , Belgium .

Remarks.—The genus differs from other linoproductids by its small dimensions and in the development of strong, subangular rugae anteriorly. It is similar to Undaria Muir-Wood and Cooper, 1960 , of the Monticuliferidae Muir-Wood and Cooper, 1960 , but it differs from it in having prominent ribs crossing rugae and a smaller umbo.

Fluctuaria undata ( Defrance, 1826)

Fig. 13G .

1826 Productus undatus ; Defrance 1826: 354.

1844 Productus tortilis ; M’Coy 1844: fig. 14.

1862 Productus undatus Defrance, 1826 ; Davidson 1862 a: 161, pl. 34: 7–12,?13. (cum syn.)

1960 Fluctuaria undata ( Defrance, 1826) ; Muir-Wood and Cooper 1960: pl. 115: 11–20.

1965 Fluctuaria undata ( Defrance, 1826) ; Muir-Wood 1965: fig. 373: 3.

1991 Fluctuaria undata ( Defrance, 1826) ; Brunton and Tilsley 1991: 291.

2000 Fluctuaria undata ( Defrance, 1826) ; Brunton et al. 2000: fig. 366: 2a–d.

2019 Fluctuaria undata ( Defrance, 1826) ; Yuan et al. 2019: fig. 4E.

Material.—One ventral valve: MPUM 11926 ( RCC 300-14) from mud mound complex of Ricklow Quarry, Monyash, Derbyshire, UK, Monsal Dale Limestone Formation, Brigantian, upper Visean.

Description.—Small, suboval shell. Cardinal margin straight; maximum width at shell mid-length. Anterior commissure rectimarginate. Ventral valve regularly convex.

Ventral valve surface covered by fine, rounded ribs with narrow interspaces. Ribs increase anteriorly by intercalation, by bifurcation on flanks. They number 13 per 5.0 mm at the anterior commissure. Low, asymmetrical, subangular rugae on the entire ventral valve. Rugae number 13–14 in 5.0 mm near umbo, 4–5 in 5.0 mm near anterior commissure. Ribs cross rugae.

Remarks.—The specimen is assigned to Fluctuaria undata based on its small size and ornamentation of prominent thin ribs crossing subangular rugae. The density of ribs is similar to that reported by Davidson (1862 a: 161).

Stratigraphic and geographic range.— Fluctuaria undata is recorded from the Mississippian of Northumberland ( Davidson 1862 a), the Visean of the Isle of Man ( Muir-Wood and Cooper 1960), and the Asbian–Brigantian (upper Visean), of Derbyshire and Yorkshire ( Brunton and Tilsley 1991; this study) in England. Davidson (1862 a) also recorded some specimens from Scotland and Ireland. The species is also recorded from the upper Visean of Visé, Belgium ( Muir-Wood and Cooper 1960), the Mississippian of Ukraine ( Ohar 2021), the Serpukhovian of Kazakhstan, the Visean of Tibet, the upper Visean of the Urals region ( Chen 2004), and the upper Visean–Serpukhovian of China ( Chen 2004; Yuan et al. 2019; Shen et al. 2017).

Figures

Fig. 13. Echinoconchidae, Linoproductidae, Monticuliferidae, Orthotetida, and Orthida from the Brigantian (uppermost Visean) of Ricklow Quarry, near Monyash, Derbyshire, UK (localities RCC-, RCK-; see Fig. 3). A. Echinoconchus punctatus (Sowerby, 1822), MPUM11976 (RCK15-47) in ventral view. B–D. Pustula cf. pustulosa (Phillips, 1836), B. MPUM11989 (RCC128-17a) dorsal valve external cast. C. MPUM11987 (RCC41-1) in ventral view. D. MPUM11988 (RCC128-7) in ventral (D1) and dorsal (D2) views. E, F. Linoprotonia sp. E. MPUM11991 (RCC42-17) in ventral (E1) and lateral E2) views. F. MPUM11992 (RCC60-59) in ventral view. G. Fluctuaria undata (Defrance, 1826), MPUM11926 (RCC300-14) ventral valve in ventral view. H.?Serratocrista aff. dalriensis McIntosh, 1974, MPUM11997 (RCC10-40) ventral valve in ventral view. I. Schellwienella sp., MPUM11995 RCC36-12) ventral valve in ventral view. J, K. Schizophoria (Schizophoria) cf. connivens (Phillips, 1836). J. MPUM12009 (RCC60-48) in ventral view. K. MPUM12010 (RCC1B-7) dorsal valve in dorsal view. L–O. Schizophoria (Schizophoria.) resupinata (Martin, 1809). L. MPUM12003 (RCC1B-4) dorsal valve in dorsal view. M. MPUM11999 (RCC1B-26) in dorsal view. N. MPUM12004 (RCC1B-25) dorsal valve in dorsal view. O. MPUM12005 RCC36-1a) dorsal valve in dorsal view. Scale bars 10 mm.