A New Sea Spider (Arthropoda: Pycnogonida) With a Flagelliform Telson From the Lower Devonian Hunsrück Slate, Germany

Abstract

A new Lower Devonian sea spider (Arthropoda: Pycnogonida) from the Hunsrück Slate, Germany, is described as Flagellopantopus blocki gen. et sp. nov. This is only the sixth fossil pycnogonid species to be described. Its most remarkable and unique aspect is the long, flagelliform telson. Although our fossil apparently lacks chelifores (an apomorphy), the retained telson and the segmented trunk end behind the last pair of legs resolve F. blocki to a fairly basal position in the pycnogonid stem lineage. It probably lies between Palaeoisopus problematicus Broili, which has a lanceolate telson and the most trunk segments of any sea spider, and all other Silurian-Recent Pycnogonida. Our new material shows that at least two fossil pycnogonids retained a telson, albeit with very different morphologies, and further supports the idea that a greater diversity of body plans existed among the Palaeozoic pycnogonid taxa.

Phylogeny of the sea spiders (Arthropoda, Pycnogonida) based on direct optimization of six loci and morphology

“…The sister group relationships of fossil pycnogonids with the Ascorhychus + Eurycyde clade are not strongly supported though, thus no definite classification is to be made, but the results suggest the possibility of more plesiomorphic conditions in living taxa compared with the extinct taxa known so far. Pycnogonid fossils known so far and those waiting to be described might be more diverse and of more derived condition than previously recognized (Poschmann and Dunlop, 2006). The inclusion of a recently described Devonian pycnogonid with a flagelliform telson (Poschmann and Dunlop, 2006) in future analyses might challenge this hypothesis and will surely provide alternative hypothesis regarding homologies in abdomen segmentation and the relationship among fossil taxa.…”

“…Pycnogonid fossils known so far and those waiting to be described might be more diverse and of more derived condition than previously recognized (Poschmann and Dunlop, 2006). The inclusion of a recently described Devonian pycnogonid with a flagelliform telson (Poschmann and Dunlop, 2006) in future analyses might challenge this hypothesis and will surely provide alternative hypothesis regarding homologies in abdomen segmentation and the relationship among fossil taxa.…”

“…The uncertain origin of the ''obscure'' sea spiders, is part of, as recently expressed, ''one of the most controversial of all zoological topics'' (Budd and Telford, 2005). This controversy is continuing and being fueled by a flow of recent data such as phylogenetic data sets (Arango, 2003a), the characterization and interpretation of larval anatomy and neurobiology (Vilpoux and Waloszek, 2003;Maxmen et al, 2005), the description of new fossils (Siveter et al, 2004;Poschmann and Dunlop, 2006), and more recently, hox gene expression data Manuel et al, 2006). Maxmen et al (2005) provided an interpretation of novel neuroanatomical data from an Anoplodactylus species (i.e., A. eroticus, see details in Arango and Maxmen, 2006), suggesting chelifores are innervated by the protocerebrum and are not homologous to chelicerae, which are deutocerebral.…”

Segmentation and tagmosis in Chelicerata

“…In the contemporary Hunsrück sea spider Flagellopantopus blocki Poschmann and Dunlop, 2006 there is an obvious trend for the trunk behind the last pair of legs to become shorter and more compact (Poschmann and Dunlop, 2006). Chelicerae in F. blocki are either not preserved or are genuinely absent (Fig.…”

Ichnological Insights Into Mitrate Palaeobiology

“…Soft tissue preservation is yet to be documented for Rhenocystis , but the skeleton of specimens is typically nearly complete (Ruta and Bartels 1998). As with other components of the Hunsrück fauna, it is difficult to establish the stratigraphic position of Rhenocystis with greater precision, as specimens were collected from loose slabs split off during slate production (Ruta and Bartels 1998; Poschmann and Dunlop 2006).…”