Long-held ideas regarding the evolutionary relationships among animals have recently been upended by sometimes controversial hypotheses based largely on insights from molecular data. These new hypotheses include a clade of moulting animals (Ecdysozoa) and the close relationship of the lophophorates to molluscs and annelids (Lophotrochozoa). Many relationships remain disputed, including those that are required to polarize key features of character evolution, and support for deep nodes is often low. Phylogenomic approaches, which use data from many genes, have shown promise for resolving deep animal relationships, but are hindered by a lack of data from many important groups. Here we report a total of 39.9 Mb of expressed sequence tags from 29 animals belonging to 21 phyla, including 11 phyla previously lacking genomic or expressed-sequence-tag data. Analysed in combination with existing sequences, our data reinforce several previously identified clades that split deeply in the animal tree (including Protostomia, Ecdysozoa and Lophotrochozoa), unambiguously resolve multiple long-standing issues for which there was strong conflicting support in earlier studies with less data (such as velvet worms rather than tardigrades as the sister group of arthropods), and provide molecular support for the monophyly of molluscs, a group long recognized by morphologists. In addition, we find strong support for several new hypotheses. These include a clade that unites annelids (including sipunculans and echiurans) with nemerteans, phoronids and brachiopods, molluscs as sister to that assemblage, and the placement of ctenophores as the earliest diverging extant multicellular animals. A single origin of spiral cleavage (with subsequent losses) is inferred from well-supported nodes. Many relationships between a stable subset of taxa find strong support, and a diminishing number of lineages remain recalcitrant to placement on the tree.

Currently, between one-third and two-thirds of marine species may be undescribed, and previous estimates of there being well over one million marine species appear highly unlikely. More species than ever before are being described annually by an increasing number of authors. If the current trend continues, most species will be discovered this century.

BackgroundInvertebrate nervous systems are highly disparate between different taxa. This is reflected in the terminology used to describe them, which is very rich and often confusing. Even very general terms such as 'brain', 'nerve', and 'eye' have been used in various ways in the different animal groups, but no consensus on the exact meaning exists. This impedes our understanding of the architecture of the invertebrate nervous system in general and of evolutionary transformations of nervous system characters between different taxa.ResultsWe provide a glossary of invertebrate neuroanatomical terms with a precise and consistent terminology, taxon-independent and free of homology assumptions. This terminology is intended to form a basis for new morphological descriptions. A total of 47 terms are defined. Each entry consists of a definition, discouraged terms, and a background/comment section.ConclusionsThe use of our revised neuroanatomical terminology in any new descriptions of the anatomy of invertebrate nervous systems will improve the comparability of this organ system and its substructures between the various taxa, and finally even lead to better and more robust homology hypotheses.

The field of systematics has developed remarkably over the last few decades. A multitude of new methods and contributions from diverse biological fields — including molecular genetics and developmental biology — have provided a wealth of phylogenetic hypotheses, some confirming traditional views and others contradicting them. There is now sufficient evidence to draw up a ‘tree of life’ based on fairly robust phylogenetic relationships. This book aims to apply these new phylogenies to an evolutionary interpretation of animal organ systems and body architecture. Organs do not appear suddenly during evolution: instead they are composed of far simpler structures. In some cases, it is even possible to trace particular molecules or physiological pathways as far back as pre-animal history. What emerges is a fascinating picture, showing how animals have combined ancestral and new elements in novel ways to form constantly changing responses to environmental requirements. The book starts with a general overview of animal systematics to set the framework for the discussion of organ system evolution. The chapters deal with the general organization, integument, musculature, nervous system, sensory structures, body cavities, excretory, respiratory and circulatory organs, the intestinal and reproductive system, and spermatozoa. Each organ system is presented with its function, the diversity of forms that are realized among metazoan animals, and the reconstruction of its evolution.

Several anecdotal reports in the literature have suggested that insects parasitized by hairworms (Nematomorpha) commit `suicide' by jumping into an aquatic environment needed by an adult worm for the continuation of its life cycle. Based on 2 years of observations at a swimming pool in open air, we saw this aberrant behaviour in nine insect species followed by the emergence of hairworms. We conducted field and laboratory experiments in order to compare the behaviour of infected and uninfected individuals of the cricket Nemobius sylvestris. The results clearly indicate that crickets infected by the nematomorph Paragordius tricuspidatus are more likely to jump into water than uninfected ones. The idea that this manipulation involved water detection from long distances by infected insects is not supported. Instead, our observations suggest that infected insects may first display an erratic behaviour which brings them sooner or later close to a stream and then a behavioural change that makes them enter the water.