Tuesday 9 December 2014

A new species of Brittle Star from the Early Carboniferous of Poland.

Brittle Stars, Ophiuroidea, are five-limbed Echinoderms related to Starfish and having a similar body-plan. However while the five limbs of the Starfish are rigid extensions of the central disk, and movement is achieved by means of tube-feet on the underside of the animal, the limbs of Brittle Stars are fully articulated and used for locomotion. The fossil record of Brittle Stars goes back to at least the Early Ordovician, though these Palaeozoic Brittle Stars have not been extensively studied.

In a forthcoming paper in the journal Acta Palaeontologica Polonica available online from 26 November 2014, Ben Thuy of the Department of Palaeontology at the Natural History Museum of Luxembourg, Manfred Kutscher of Sassnitz in Germant and Bartosz Płachno of the Department of Plant Cytology and Embryology at Jagiellonian University describe a new species of Brittle Star from the Early Carboniferous Mazurowe Doły Formation at Czatkowice Quarry on the Dębnik Massif in southern Poland.

The new species is placed in the genus Aganaster and given the specific name jagiellonicus, in honour of Jagiellonian University, which is the oldest in Poland and one of the oldest in Europe, and of the Jagiellonian Dynasty of Polish Kings. The species is described from a single specimen preserved on a slab of limestone, with a central disk 9 mm in diameter, and all five arms preserved, though most have their tips missing the longest arm being 45 mm in length.

Aganaster jagiellonicus from the upper Tournaisian to lower Visean (Lower Carboniferous) Mazurowe Doły Formation, Rudawa Group of Czatkowice Quarry, Dębnik Massif, southern Poland. General view of the specimen,exposing the ventral side. Thuy et al. (2014).

The genus Aganaster is previously known from the Carboniferous of North America and the Permian of China. It is thought to be closely related to the genus Archaeophiomusium, which is known from the Permian of North and South America. A review of Palaeozoic Brittle Stars in 2004 suggested that these two genera should be placed in the modern group Ophiolepididae, though this group has since been shown to be polyphyletic (i.e. not all its members were more closely related to one-another than they were to anything else). However Thuyet al. contend that a fresh review of the group would still place them within a modern family, and that therefore the diversification of Brittle Stars into modern groups must have happened before the Carboniferous.

See also…

Brittle Stars (Ophiuroidea) are five-limbed Echinoderms superficially resembling Starfish (Asteroidea). Like Starfish they posses (usually) five limbs arranged around a central disk which houses the mouth and anus, but the limbs of Brittle Stars are clearly...

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