High-level phylogeny and evolution
The book "Animal Evolution: Interrelationships of the Living Phyla" has been completed* (C. Nielsen). A data matrix of phylogenetically important characters has been extracted from this book and a series of phylogenetic analyses using computer programs such as Henning86, PAUP, Nona, and PeeWee have been performed. The importance of the interpretation of the characters and their coding in the data matrix were discussed* (C. Nielsen and D. Eibye-Jacobsen, with N. Scharff, Entomology Department). A discussion of the reliability of molecular data for phylogenetic reconstruction has been initiated (C. Nielsen, with A. Adoutte and H. Philippe, Université Paris Sud, and G. Balavoine, Wellcome Institute, Cambridge).
The phylogenetic relationships of annelids and a number of related phyla have been discussed in response to a paper by Rouse & Fauchald (1995); both the data matrix of these authors and the influence of the use of paraphyletic groups in their cladistic analysis were criticized* (D. Eibye-Jacobsen, C. Nielsen).
Manuscripts have been prepared in connection with lectures in London (The phylogenetic position of the arthropods)* and Paris (Animal classification - then and now)* (C. Nielsen). A review with the title "Origin and evolution of the metazoan life cycle" has been completed. The main conclusions are that the ancestral metazoan life cycle was holopelagic and that pelago-benthic life cycles evolved independently in Cnidaria, Protostomia and Deuterostomia; lecithotrophic larvae and direct development can be shown to have evolved in numerous lines. Loss of larval organs, such as the tail of the ascidian tadpole larva, has been shown to happen through a shift in one gene, whereas the evolution of a complicated larval organ must be a much more intricate process (C. Nielsen).
Preliminary SEM and TEM studies of ontogenetic development and organization of the ciliary bands of annelid and mollusc larvae have been carried out during two stays at Friday Harbor Laboratories, WA, USA (C. Nielsen, with Ĺ. Jespersen, Zoological Inst.).