Send to

Choose Destination
See comment in PubMed Commons below
Proc Natl Acad Sci U S A. 1997 Jul 22;94(15):8006-9.

Molecular evidence that echiurans and pogonophorans are derived annelids.

Author information

  • 1Section of Ecology and Systematics, Cornell University, Ithaca, NY 14853, USA.


The Annelida, which includes the polychaetes and the clitellates, has long held the taxonomic rank of phylum. The unsegmented, mud-dwelling echiuran spoon worms and the gutless, deep-sea pogonophoran tube worms (including vestimentiferans) share several embryological and morphological features with annelids, but each group also has been considered as a separate metazoan phylum based on the unique characters each group displays. Phylogenetic analyses of DNA sequences from the nuclear gene elongation factor-1alpha place echiurans and pogonophorans within the Annelida. This result, indicating the derived loss of segmentation in echiurans, has profound implications for our understanding of the evolution of metazoan body plans and challenges the traditional view of the phylum-level diversity and evolutionary relationships of protostome worms.

[PubMed - indexed for MEDLINE]
Free PMC Article
PubMed Commons home

PubMed Commons

How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for HighWire Icon for PubMed Central
    Loading ...
    Support Center