Lingulosacculus nuda, Balthasar & Butterfield, 2009
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publication ID |
https://doi.org/ 10.4202/app.2008.0042 |
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persistent identifier |
https://treatment.plazi.org/id/03DA87D8-DB2D-FF99-FCA3-FD9DFC54FC93 |
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treatment provided by |
Felipe |
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scientific name |
Lingulosacculus nuda |
| status |
sp. nov. |
Lingulosacculus nuda sp. nov.
Figs.1 View Fig , 2 View Fig .
Etymology: Latin nuda , naked, alluding to the lack of mineralisation.
Type material: Holotype, GSC−34953 (part and counterpart).
Type locality: Mumm Peak section (53 ° 11’97’’ N, 119 ° 08’84’’ W), Jasper National Park, Alberta, Canada .
Type horizon: Early Cambrian, Waucoban series, Dyeran stage, “ Nevadella ” Zone, Mural Formation
Material.— Holotype plus one other specimen (GSC−34952), both from the same layer.
Diagnosis.—Dorsal valve elongate oval, maximum width somewhat anterior of midline; ventral valve elongate dropshaped with maximum thickness in the anterior part at about 75% of its length; small opening angle of the ventral pseudointerarea (around 25 °).
Measurements.—The maximum width is 13 mm (GSC−34953) and 12 mm (GSC−34952), the maximum length of the most complete specimen is 32 mm (GSC−34953 counterpart), and the oval anterior part is 14 mm (GSC−34952) and 15 mm (GSC−34953) long.
Description.— Lingulosacculus nuda has an anteriorly rounded conical shape which in GSC−34952 ( Fig. 1A View Fig ) consists of two distinct elements: a larger conical valve and a smaller, superimposed oval valve that matches the anterior part of the conical valve. GSC−34953 ( Fig. 1B View Fig ) shows the reverse aspect of the larger conical valve, with the smaller oval valve only visible where it protrudes at the anterior margin.
The oval valve in GSC−34952 ( Fig. 1A View Fig ) is medially subdivided by a parallel−sided furrow that widens into a funnel−shape in the posterior third of the valve. Dark stains run in diffuse bands parallel to the outer margin of the median furrow and slightly diverge at the anterior end. Another set of diffuse dark stains runs approximately parallel to the outer margin of the valve ( Fig. 1A View Fig ). Under low−angle light, two curved ridges can be observed in front of the anterior end of the median furrow, originating from opposite sides of the median furrow ( Fig. 2 View Fig ). The left ridge extends slightly beyond the valve margin.
The larger conical valve is best preserved in GSC−34953 ( Fig. 1B View Fig ) and has an anterior oval portion that is darker than the tapering posterior extension. The posterior part of this oval part exhibits a distinct triangular− to funnel−shaped area, while its posterior margin exhibits two straight edges that run obliquely inwards (white arrows in Fig. 1B 1 View Fig ). The tapering posterior extension originates at about the maximum width of the valve and then tapers backwards to form an elongate cone. It includes a distinct dark line that originates in the anterior oval part of the valve and extends through the first two thirds of the posterior extension before twice looping back on itself ( Fig. 1B View Fig ).
In GSC−34952 ( Fig. 1A View Fig ), only the tapering posterior part of the larger valve is visible as the anterior part is overlain by the oval valve. The outline of the posterior extension is visible as a clear line that demarcates the fossil from the brighter rock matrix. Inside the posterior extension a darker triangular area forms the continuation of the funnel−shaped area in posterior part of the oval valve.
Remarks.—The morphology of Lingulosacculus nuda is closely comparable with that of exceptionally preserved linguliform brachiopods from the Chengjjiang biota of South China (Zhang et al. 2007), most notably in the triangular body cavity at the posterior part of the shorter oval valve and the oval portion of the elongate valve. The median furrow of the short oval valve can be readily identified as the anterior projection regularly encountered on the dorsal valves of many linguliform brachiopod groups, while the short curved ridges are in the correct position and of the right size to represent the partially preserved arms of a lophophore. Together with the diverging dark stain at its anterior end (interpretable as a brachiopod vascula media; Fig. 1A View Fig ) and the dark staining along the lateral margin (vascula lateralia; Fig. 1A View Fig ), these features make a clear case for identifying L. nuda as a linguliform brachiopod ( Fig. 3 View Fig ).
The conical posterior extension of L. nuda 's ventral valve is directly comparable to the ventral pseudointerarea of fossil Lingulellotretidae , a family of organophosphatic brachiopods known from four Early Cambrian to Early Ordovician genera ( Jin et al. 1993; Holmer et al. 1997; Holmer and Popov 2000). In this light, the straight oblique edges along the anterior margin of the posterior extension in L. nuda (white arrows in Fig. 1B 1 View Fig ) can be identified as the margins of the propareas of the ventral pseudointerarea. In the Lingulellotretidae the ventral pseudointerarea forms a closed posterior outgrowth that extends well beyond the hinge−line and is known to accommodate a significant portion of the body cavity, including the posterior loop of the gut (Zhang et al. 2007). This same arrangement occurs in L. nuda , with the looped dark line tracking the same course as the exceptionally preserved guts of Chengjiang lingulellotretids, including the median position of its posterior loop and the sharp right turn as it exits the posterior extension of the ventral valve (cf., Zhang et al. 2007: fig. 2C); the anterior end of the gut in GSC−34953 ( Fig. 1B View Fig ), however, has been broken and is now curled back and folded over itself. Lingulosacculus nuda is also presumed to have had a long fleshy pedicle, comparable to that of Chengjiang lingulellotretids (see Jin et al. 1993; Zhang et al. 2007), but neither of the specimens preserves the posterior−most tip of the ventral valve.
The conspicuous two−dimensionality of L. nuda stands in sharp contrast to co−occurring, three−dimensionally preserved lingulid and mickwitziid brachiopods, but is directly comparable to co−occurring Vetulicola and Anomalocaris claws, both of which are widely accepted as lacking any primary biomineralisation. Unless it was originally mineralised by aragonite—which is not three−dimensionally preserved in co−occurring hyolithids—there is little doubt that L. nuda was soft−shelled.
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