Hadrotreta sp.

Skovsted, C. B., Knight, I., Balthasar, U. & Boyce, W. D., 2017, Depth related brachiopod faunas from the lower Cambrian Forteau Formation of southern Labrador and western Newfoundland, Canada, Palaeontologia Electronica (Oxford, England: 1990) 17 (15), pp. 1-52 : 42-43

Hadrotreta sp.

Figure 22

Material. Four specimens from the lower patch reef complex of southern Labrador and the Devils Cove member at Mount St. Margaret in western Newfoundland, west of the Long Range Mountains (MSM-3, ICS1553 , ICS1577 ) .

Description. A handful of acrotretid ventral valves of presumed sub-circular outline, no specimen preserves the complete margin of the shell and its shape is difficult to determine ( Figure 22.2-3 ). The pedicle foramen is situated at the margin of the larval shell and drop-shaped ( Figure 22.4 ). The ventral pseudointerarea is procline with a narrow, parallell-sided intertrough ( Figure 22.1, 22.3 ). The internal morphology is revealed in a single specimen showing a large apical process anterior of the pedicle tube, deep apical pits lateral to the pedicle tube and deeply impressed, straight vascula lateralia ( Figure 22.5-6 ). A narrow central ridge extends anteriorly from the apical process and on each side three smaller ridges are present between the central ridge and the vascula lateralia. The ornament of the larval shell unknown and the adult shell is ornamented by fine fila ( Figure 22.4 ).

Remarks. A small number (N=4) of ventral valves of an acrotretid brachiopod from the Devils Cove member at Mt. St. Margaret and the lower patch reef complex of southern Labrador differ from Hadrotreta taconica by the strongly procline ventral pseudointerarea with a narrow intertrough, the central ridge extending from the apical process and the position of the apical pits lateral to the internal opening of the pedicle tube. It was not possible to identify the associated dorsal valve of this species. Due to the small number of specimens and the lack of knowledge of the dorsal valve morphology, this species is left under open nomenclature as Hadrotreta sp.

Distribution. Assemblage 1, Devils Cove member and Middle shale, Forteau Formation of southern Labrador and western Newfoundland.

Figures

FIGURE 22. Hadrotreta sp. from the Forteau Formation of southern Labrador and western Newfoundland. 1-2, Ventral valve NFM F-2552 from sample ICS1553; 1, oblique posterior view showing procline pseudointerarea; 2, external view. 3-4, Ventral valve NFM F-2553 from sample ICS1577; 3, external view; 4, detail of larval shell with drop-shaped pedicle foramen. 5-6, Ventral valve NFM F-2554 from Lower shale, Mount St. Margaret, sample MSM-3; 5, internal view showing vascula lateralia and apical process; 6, oblique anterior view showing apical pits and internal opening of pedicle foramen. Scalebars equal 500 µm in figure 3, 200 µm in figures 1-2, 5-6 and 100 µm in figure 4.