Pleurotomaria DeFrance, 1826 (Gastropoda,Mollusca) from the Lower Bajocian (Middle Jurassic) sediments of Luxembourg,with considerations on its systematics,evolution and palaeobiogeographical history

Abstract: Pleurotomaria species from lower Bajocian (Middle Jurassic) sediments of south‐western Luxembourg housed in the National Natural History Museum of Luxembourg are described. Seven species are recognized, one of which is new, Pleurotomaria faberi sp. nov. A more detailed definition of the diagnostic characters of the genus is proposed and the morphological continuity between Talantodiscus and Pleurotomaria is demonstrated, suggesting that the former cannot be considered as a distinct taxon. The palaeoecology, evolution and palaeobiogeographical history of Pleurotomaria are outlined. Pleurotomaria presumably first appeared in late Middle Triassic of New Zealand where it underwent a relative diversification up to the Hettangian (Early Jurassic). From early Hettangian, most of its evolutionary history took place in Europe and western Tethys. In the European epicontinental seas, Pleurotomaria experienced two important radiations. The first occurred in the Early Jurassic, with a peak in the late Pliensbachian, and was marked by an expansion of the distribution to the central part of western Tethys. After a collapse in species diversity, probably related to the early Toarcian anoxic event, a second radiation occurred. This culminated in the early Bajocian and was mainly confined in a region encompassing southern England, Paris Basin and southern Germany. Low‐spired species, formerly attributed to Talantodiscus, probably originated independently and iteratively during the history of Pleurotomaria. The facies and associated benthic faunas suggest that Pleurotomaria probably lived on shallow soft bottoms composed of mixed calcareous–siliciclastic sediments. The two main Early Jurassic and early Middle Jurassic radiations of the genus took place in these environments. Records of the genus in Jurassic carbonate platform deposits are very few and concern mainly post‐Bajocian species.     

四种翁戎螺的齿舌形态及功能

翁戎螺（Pleurotomariidae）起源于寒武纪时期,是介于软体动物祖先和现代腹足类之间的过渡类型。目前我国翁戎螺的分类、生态等方面研究不足,为探究翁戎螺的形态分类及食性,以寺町翁戎螺（Bayerotrochus teramachii）、红翁戎螺（Mikadotrochus hirasei）、高腰翁戎螺（M. salmianus）和龙宫翁戎螺（Entemnotrochus rumphii）为研究对象,应用扫描电镜观察其齿舌结构。结果表明,（1）翁戎螺齿舌结构与大多数腹足类具有3种类型的齿舌不同,其齿舌带上具有中央齿、内侧齿、外侧齿、镰状齿、丝状齿和桨状齿6种不同类型的小齿。（2）4种翁戎螺的中央齿均为1枚,内侧齿2或3枚,外侧齿20 ~ 25枚,镰状齿16 ~ 32枚,丝状齿35 ~ 62枚,桨状齿10 ~ 26枚。（3）翁戎螺属（Mikadotrochus）内种类之间齿舌形态的差异较小,进行种间区分需结合其小齿数量,但属间差异较大,中央齿、内侧齿、镰状齿的齿尖和齿基形态都可以进行属间区分。（4）龙宫翁戎螺齿舌带每个横排具有26枚桨状齿,与之前研究具有10枚不同。本研究对翁戎螺镰状齿和丝状齿之间、丝状齿和桨状齿之间的过渡形态进行深入地描述和划分。本研究结果可为我国翁戎螺的形态分类研究提供资料。     

Living Pleurotomariidae (Mollusca: Gastropoda) from the South Pacific

Abstract

Perotrochus caledonicus n.sp. is described from the upper bathyal south of New Caledonia, an old area that has remained stable over the past few million years, and P. tangaroana n.sp. is described from the bathyal of Lau Ridge. These represent the first occurrence of living Pleurotomariidae in the South Pacific; other representatives of the family are restricted to Southeast Asian seas or the Atlantic.