Harttella oakleyi Brunton, 1982

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 : 909-910

publication ID	https://doi.org/ 10.4202/app.00972.2022
persistent identifier	https://treatment.plazi.org/id/41708783-FFFB-FF97-8C8B-CCDAFAEFFEEF
treatment provided by	Felipe
scientific name	Harttella oakleyi Brunton, 1982
status

Treatment

Figs. 15D–E View Fig , 17A–K View Fig .

1824 Terebratula saccula ; Sowerby 1824: 65 (pars), pl. 446: 1 top left.

1858 Terebratula sacculus Sowerby, 1824 ; Davidson 1858: 14 (pars), pl. 1: 27, 29,?30; pl. 54: 5.

1982 Harttella oakleyi ; Brunton 1982: 50, figs. 5–7.

Material.—Sixty-five articulated specimens: MPUM 12075

( RCC 10-15b); MPUM 12076 ( RCC 41-9); MPUM 12077 ( RCC 41-22); MPUM 12078 ( RCC 49-9); MPUM 12079 ( RCC 49-12); MPUM 12080 ( RCC 60-19b); MPUM 12081 ( RCC 65G-2); MPUM 12082 ( RCC 65G-8a); MPUM 12083 ( RCC 65G-11); MPUM 12084 ( RCC 65G-14); MPUM 12085 ( RCK 15-14); MPUM 12088 ( RCC 1-8a; RCC 8-12; RCC 9-1; RCC 10-7a, 15c, 33, 37; RCC 11-9b; RCC 12-20; RCC 32-5b, 28d, 36; RCC 32B-1; RCC 38A-4; RCC 41-18c, 18d, 19b, 20b; RCC 42-2, 9, 24; RCC 45-4a, 5; RCC 48-14, 31; RCC 49-20, 34; RCC 60-43; RCC 65G-1, 5, 10, 13, 21, 22, 23; RCC 65T-6; RCC 67-1, 3; RCC 73-23d, 23e, 29b; RCC 85-1c, 3; RCC 110-3f; RCC 123-3; RCC 128-8, 22; RCC 300-2; RCK 15-6, 27, 39a;

RCK 15A-1; RCK 15B-2; RCK 17-1). Twelve ventral valves: MPUM 12089 ( RCC 1-19b, 38; RCC 10-18a, 38a; RCC 11- 18; RCC 41-20c; RCC 42-27a; RCC 49-33, 39; RCC 128-6; RCC 300-15; RCK 15-20). Four dorsal valves: MPUM 12090 RCC 10-7b, 29; RCC 32-25; RCC 41-21). One fragment: MPUM 12091 ( RCC 12-10a). All from mud mound complex of Ricklow Quarry, Monyash, Derbyshire, UK, Monsal Dale Limestone Formation, Brigantian, upper Visean.

Description.—Small, ventribiconvex shell with subpentagonal elongated outline; cardinal margin curved, maximum width at shell mid-length. Anterior commissure uniplicate to weakly lobate. Shell substance punctate. Ventral umbo strongly curved; palintrope anacline. Foramen permesothyrid. Shallow, broadly rounded sulcus starting at two-thirds shell length. Dorsal palintrope anacline. Dorsal sulcus absent to weakly developed near the commissure, rarely starting at shell mid-length.

Shell smooth, with regularly concentric growth lines. Sporadic lamellae developed.

Probable presence of a pedicle collar. Dental plates absent. Dorsal valve with convex hinge plates fusing medially to form a high Y-shaped septalium.

There is variability in the shape of the ventral sulcus: most specimens have a very broad rounded sulcus, whereas a few others show a narrower one, starting from shell mid-length. There is also large variability in convexity of both valves. Juvenile shells are almost as long as wide, with a distinct subpentagonal outline and rectimarginate commissure. When a length of 6.0–9.0 mm is attained, the ventral sulcus begins to develop.

Remarks.—The specimens are close both in their morphology and internal characters to the specimens of Harttella oakleyi figured by Brunton (1982). Brunton described the species as having a ventral sulcus starting posteriorly to shell mid-length and becoming narrow anteriorly, resulting in a sharply uniplicate commissure ( Brunton 1982: 50). Most of the specimens from Ricklow Quarry commonly show a shallow sulcus starting anteriorly to shell mid-length, but there is a large morphological variability and some even show a narrow sulcus starting near umbo. The specimens are thus included in H. oakleyi and the species concept extended to include specimens with a shallow rounded ventral sulcus restricted anteriorly.

Externally, H. oakleyi resembles Balanoconcha saccula (Sowerby, 1824) . None of the specimens from Ricklow Quarry could be associated to B. saccula , which is usually larger and reaches its maximum width at two-thirds shell length, resulting in a subtriangular, rather than subpentagonal, outline.

According to Brunton and Tilsley (1991) the specimens named Girtyella saccula (= Balanoconcha saccula ) recorded by Gutteridge (1990) from the mound complex in Ricklow, are in fact H. oakleyi specimens. This is likely also the case for some of the specimens assigned by Mitchell (1971) to Dielasma hastata (Sowerby, 1824) , in his study of Visean faunas from the study area.

Stratigraphic and geographic range.— Harttella oakleyi is recorded from the Brigantian (uppermost Visean) of Derbyshire, England ( Brunton 1982; this study).