Arthropod and annelid relationships re-examined

Molecular phylogenetics of the Metazoan clade Lophotrochozoa

“…LSU sequences recover monophyly of nearly all recognized phyla sampled, including mollusks and annelids which have consistently appeared as polyphyletic in studies using SSU alone (e.g. Giribet et aI., 2000; Eernisse, 1997;Peterson and Eemisse, 2001). This increase in resolution provides a tool by which we can begin to decipher deep-level relationships within…”

“…However, two independent 18S rDNA studies (Telford and Holland, 1993;Wada and Satoh, 1994) showed that chaetognaths were not closely related to other deuterostome taa suggesting that coelomic patterns and blastopore fate are not representative of the rel ationships of major metazoan lineages . Nielsen's (1995) hypothesis of deuterostome affinities for the ctenophores is inconsistent with available data (Eernisse et aI., 1992;Schram, 1991;Eernisse, 1997;Kim et al, 1997;Winnepenninckx et aI., 1998b).…”

“…Other organisms placed in the Ecdysozoa include kinorhynchs, priapulids, nematomorphs, onychophorans and tardigrades (Aguinaldo et ai., 1997). Because chaetognaths appear to be allied to nematodes , they are also presumably Eernisse et al, 1992;Aguinaldo et al, 1997;Eernisse, 1997;; see text for additional references), this topology represents a consensus ilustrating the relationships between major metazoan taxa. Many lesser-known "phyla" (e.g., gastrotrichs, acanthocephalans, placozoans, nematomorphs, etc,) were not included for simplicity or because their phylogenetic affinities are not clear.…”

“…Figure 2 shows a revised view of evolutionary relationships among major groups of metazoans. Sponges and diploblasts (cnidarians and ctenophures) are basal to the triploblastic metazoans (e.g., Eernisse et aI., 1992;Eernisse, 1997;Aguinaldo et aI., 1997;Aguinaldo and Lake, 1998;Winnipenninckx et aI., 1998b;Kim et at., 1999). When taken together, the two triploblast "superclades" Ecdysozoa (Aguinaldo et aI., 1997) and Lophotrochozoa (Halanych et aI., 1995) are usually referred to as the Protostomia (e.g., Aguinaldo and Lake, 1998).…”

“…Previous studies of lophotrochozoan relationships have relied heavily on SSU data, morphological cladistic analyses, or a combination of the two (e.g., Eemisse, 1997; Zrzavry et aI., 1998; Giribet et aI., 2000). Unfortnately, SSU data do not even cluster taxa into well-reoognized monophyletic unit!…”