Parathyasira Iredale 1930
Parathyasira Iredale, 1930 Type species. Parathyasira resupina Iredale, 1930 Diagnosis. Small to medium sized thyasirids with a weakly defined posterior area, a well-defined supramarginal sulcus without an auricle, a microsculpture of calcareous spines arranged in dense radial rows. Hinge lacking te...
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| Format: | Other/Unknown Material |
| Language: | unknown |
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2015
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| Online Access: | https://zenodo.org/record/6098571 https://doi.org/10.5281/zenodo.6098571 |
| Summary: | Parathyasira Iredale, 1930 Type species. Parathyasira resupina Iredale, 1930 Diagnosis. Small to medium sized thyasirids with a weakly defined posterior area, a well-defined supramarginal sulcus without an auricle, a microsculpture of calcareous spines arranged in dense radial rows. Hinge lacking teeth, ligament weak, in a shallow resilifer. Gills of two demibranchs, delicate, Type 2 aR of Oliver (2014). Remarks. The diagnosis here is limited to those species with a spiny micro-sculpture arranged in radial rows. There are many other species with a similar overall shell form such as the North Atlantic Thyasira equalis Verrill & Bush, 1898 that have been placed in Parathyasira by previous studies (Payne & Allen 1991; Oliver & Killeen 2002; Zelaya 2009). There remains many uncertainties concerning the relationships of these species in conjunction with many others currently placed in Thyasira but not agreeing in shell form or anatomy with the type species of Thyasira, T. flexuosa (Montagu, 1803). Further research is required to resolve how many genera should be recognized, while those with a distinct radial micro-sculpture form a coherent group. Parathyasira bamberi sp. nov. Figs 1 A–E Type material. Holotype - single live collected specimen, Off Ras Madrakah, southern Oman, Discovery cruise 211 st. 12687 #2, 18° 55.85´N 58 ° 52.17´E to 18 ° 52.16´N 59 °07.24´E, 3356 m, collected P.G. Oliver, 19 October 1994. NMW.Z. 1995.009. 13. Paratype, one fragmented shell as holotype, NMW.Z. 1995.009. 14. Description. Shell (Figs 1 A–D). Holotype 18.7 mm in length, 18.4 mm in height. Thin, fragile. Equivalve. Compressed. ~Equilateral, beaks prosogyrous, just anterior of midline. Outline subcircular, slightly longer than high. Posterior dorsal margin long, almost straight, sloping steeply; anterior dorsal margin short, slightly concave; anterior and ventral margins a continuous curve. Posterior area flattened not sulcate, demarcated by a weak radial ridge. Sub-marginal sulcus (sms = escutcheon) long, narrow, sunken, ... |
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