Phylogenetical review and biogeographic remarks on the interstitial and subterranean freshwater iberobathynells (Crustacea, Syncarida, Parabathynellidae)

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Abstract
In order to infer evolutionary patterns within iberobathynells (Parabathynellidae, Bathynellacea) a complete morphological description and population variability study of the recently described genera Guadalopebathynella Camacho and Serban, 1998 and Hexaiberobathynella Camacho and Serban, 1998, endemic to the Iberian Peninsula, are presented. We compared 14 different populations of the Hexaiberobathynella mateusi (Galhano, 1967), 12 in Spain and two in Portugal, with a new population recently ascribed to the poorly known Hexaiberobathynella hortezuelensis Camacho and Serban, 1998. All these genera show autapomorphic characteristics and a unique combination of shared derived characters that are the basis of their monophyletic status as a tribe. The origin and distribution of the genera of freshwater interstitial (stygobiont) syncarids of the tribe Iberobathynellini (Crustacea), endemic to North America (California and Texas), Iberian Peninsula, Balearic Islands and North Africa (Morocco) are considered within the scope of evolutionary biogeography. Both plate tectonics and the Boutin-Coineau two-step model of colonization and evolution, the second phase of which represents vicariance caused by the Tethys regressions, are used to understand the evolutionary history of freshwater stygobiont iberobathynell species. Correlation between time of the last marine regression for each generic range today, and order of derivation in the phylogenetic trees show it is not significant. From these results we cannot reject the possibility that the evolutionary clade divergence within iberobathynells is independent of sea level changes and therefore we can neither accept nor reject their correlation.