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Systematics of Grania (Clitellata: Enchytraeidae), an interstitial annelid taxon

Doctoral thesis
Authors Pierre De Wit
Date of public defense 2010-03-05
ISBN 978-91-628-8012-5
Publication year 2010
Published at Department of Zoology
Language en
Keywords Clitellata, Oligochaeta, Enchytraeidae, Grania, interstitial habitat, systematics, phylogeny, DNA barcoding, cryptic species
Subject categories Natural Sciences


In between the grains of sand on the ocean floor, there exists a world which few people are aware of. Representatives of almost all animal phyla can be found here. The clitellate family Enchytraeidae is in the marine interstitial environment represented in large part by species of a genus called Grania, which are long slender worms found in marine sands throughout the world. This thesis is a study on the systematics of these worms. The body wall of Grania is searched for phylogenetically informative morphological characters. It is found that the cuticular morphological variation seen in naidids is absent, but the collagen fiber thickness varies between Grania species. Also, the circular and outer, triangular longitudinal musculature is reduced compared to that of closely related taxa while the inner, ribbon-shaped longitudinal muscle fibers are well-developed, possibly an adaptation to interstitial life. The Grania-fauna of the Great Barrier Reef is investigated, with four new species described and Grania trichaeta re-described. The phylogenetic position of Grania within the family Enchytraeidae is elucidated by molecular means, where Lumbricillus arenarius is shown to be a close relative of a monophyletic Grania. Within the genus, a molecular phylogeny is inferred of a sample of 19 species, showing considerable morphological homoplasy, while geographical distribution is concordant with the phylogeny. Thus, we combine morphology with geography, while using the DNA-based tree as a backbone constraint, to estimate a phylogeny of all 71 currently described species within the genus. Finally, the genetic variation within Scandinavian species of Grania is studied with the resulting find of a cryptic species, and the realization that although intraspecific variation generally is low, deviant individuals exist. Within this study, we also infer a phylogeny of the Scandinavian species of Grania, which seems to be a monophyletic group, and discuss their morphological character evolution.

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