43e.1 Arthropods, diverse and ancient, are a challenging group to classify.
- The Challenge of Unraveling Metazoan Phylogeny.
Despite the development of new techniques, scientists are still researching the phylogenies of many metazoan groups.
Arthropod Evolution: Background. Arthropods are extremely diverse and one of the oldest animal groups.
Arthropod Classification: Background. A classification proposed in the 1930s is recently being challenged.
43e.2 Four types of studies are revolutionizing arthropod classification.
- Morphological Studies of Arthropod Phylogeny. Studies of arthropod nervous systems suggest arthropod monophyly and a close relationship between insects and crustaceans.
- Molecular Studies of Arthropod Phylogeny.
Studies of arthropod genes suggest that crustaceans and insects constitute a sister group, exclusive of the myriapods.
- Emerging Views from Developmental Studies.
Hox gene expression patterns can reflect paths of evolution.
- New Paleontological Data.
New fossil finds indicate that crustaceans are the oldest arthropods.
43e.3 Taxonomists have also been reevaluating related groups.
- Pentastomids and Onychophorans. Pentastomids may be modified crustaceans, and onychophorans are more common in early fossils than was thought.
43e.4 Current views of arthropod diversity and classification.
- Arthropod Abundance and Classification. Many forces have driven the radiation and success of arthropods, and crustaceans may have been the earliest arthropods, giving rise to the other arthropod groups.