The phylogenetic position of the Aeolosomatidae and Parergodrilidae, two enigmatic oligochaete-like taxa of the 'Polychaeta', based on molecular data from 18S rDNA sequences

Abstract

The Aeolosomatidae and the Parergodrilidae are meiofaunal Annelida showing different combinations of clitellate‐like and non‐clitellate character states. Their phylogenetic positions and their systematic status within the Annelida are still in debate. Here we attempt to infer their systematic position using 18S rDNA sequences of the aeolosomatid Aeolosoma sp. and the parergodrilid Stygocapitella subterranea and several other meiofaunal taxa such as the Dinophilidae, Polygordiidae and Saccocirridae. The data matrix was complemented by sequences from several annelid, arthropod and molluscan species. After evaluation of the phylogenetic signal the data set was analysed with maximum‐parsimony, distance and maximum‐likelihood algorithms. Sequences from selected arthropods or molluscs were chosen for outgroup comparison. The resolution of the resulting phylogenies is discussed in comparison to previous studies. The results do not unequivocally support a sister‐group relationship of Aeolosoma sp. and the Clitellata. Instead, depending on the algorithms applied, Aeolosoma clusters in various clades within the polychaetes, for instance, together with eunicidan species, the Dinophilidae, Harmothoë impar or Nereis limbata. The position of Aeolosoma sp. thus cannot be resolved on the basis of the data available. S. subterranea always falls close to a cluster comprising Scoloplos armiger, Questa paucibranchiata and Magelona mirabilis, all of which were resolved as not closely related to both Aeolosoma sp. and the Clitellata. Therefore, convergent evolution of clitellate‐like characters in S. subterranea and hence in the Parergodrilidae is suggested by our phylogenetic analysis. Moreover, the Clitellata form a monophyletic clade within the paraphyletic polychaetes.

Trochophora larvae: Cell‐lineages, ciliary bands, and body regions. 1. Annelida and Mollusca

“…The main disagreement seems to be whether the ancestral larva was feeding or not. Mapping of larval types onto a phylogeny is problematic due to the lack of a generally accepted phylogeny of the Annelida (compare Rouse and Fauchald, '97;Westheide et al, '99;Giribet et al, 2000;Peterson and Eernisse, 2001;Struck et al, 2002;Bleidorn et al, 2003). However, the observations of two types of ciliary feeding in larvae of Armandia and Urechis (Miner et al,'99; see above) with the downstreamcollecting method used by the early stages indicate that the various other types of ciliary feeding described above are derived.…”

DNA barcoding of marine polychaetes species of southern Patagonian fjords

“…In this sense, while many studies have used the COI gene for evaluating explicit phylogenetic hypotheses, they have not examined the properties of DNA barcoding as a molecular tool for evaluating species identification (e.g., Nylander et al 1999, Dahlgren et al 2000, Struck et al 2002, Nygren & Sundberg 2003, Jördens et al 2004, Nygren et al 2005, Wiklund et al 2005, Halanych & Janosik 2006, Ruta et al 2007. These studies encountered problems with the use of this gene, for example, a low phylogenetic signal for resolving closed relationship among polychaetes, and conclude that the COI region is not useful, when used alone, for inferring phylogenetics relationship among polychaetes.…”

Ultrastructure of the ventral pharynx in the interstitial annelid Questa paucibranchiata (Orbiniidae) and its phylogenetic significance

“…Thus, most likely the observations in S. armiger are considered to stand for the entire taxon Orbiniidae. In molecular phylogenetic analyses, Parergodrilidae is mostly found as sister to the orbiniid clade (Struck et al 2002;Bleidorn 2005;Bleidorn et al 2003Bleidorn et al , 2009. Although differing in structure from the ventral pharynx present in Orbiniidae, the organ in Parergodrilidae most likely can be derived from this pharynx (Purschke 1987(Purschke , 1988a.…”