On the origin of the Hirudinea and the demise of the Oligochaeta

Abstract

The phylogenetic relationships of the Clitellata were investigated with a data set of published and new complete 18S rRNA gene sequences of 51 species representing 41 families. Sequences were aligned on the basis of a secondary structure model and analysed with maximum parsimony and maximum likelihood. In contrast to the latter method, parsimony did not recover the monophyly of Clitellata. However, a close scrutiny of the data suggested a spurious attraction between some polychaetes and clitellates. As a rule, molecular trees are closely aligned with morphology-based phylogenies. Acanthobdellida and Euhirudinea were reconciled in their traditional Hirudinea clade and were included in the Oligochaeta with the Branchiobdellida via the Lumbriculidae as a possible link between the two assemblages. While the 18S gene yielded a meaningful historical signal for determining relationships within clitellates, the exact position of Hirudinea and Branchiobdellida within oligochaetes remained unresolved. The lack of phylogenetic signal is interpreted as evidence for a rapid radiation of these taxa. The placement of Clitellata within the Polychaeta remained unresolved. The biological reality of polytomies within annelids is suggested and supports the hypothesis of an extremely ancient radiation of polychaetes and emergence of clitellates.

In search ofMarionina(Clitellata, Enchytraeidae): A taxonomic history of the genus and re‐description of the type speciesPachydrilus georgianusMichaelsen, 1888

“…In the last decade, the access to DNA sequence data has revealed phylogenetic relationships among various clitellate groups that were not obvious from analyses of morphological characters alone (Siddall & Burreson 1998;Trontelj et al 1999;Martin et al 2000;Martin 2001;Siddall et al 2001;Erséus & Källersjö 2004;Erséus 2005;Sjö lin et al 2005;Envall et al 2006). It can be expected that molecular systematics will be an important instrument to resolve many of the old controversies in enchytraeid taxonomy as well.…”

Fossil clitellate annelid cocoons and their microbiological inclusions from the Eocene of Seymour Island, Antarctica

“…Their anatomical simplicity and the plasticity of key morphological characters of the body hinder precise taxonomic resolution of groups within extant Clitellata (Novo et al, 2011). Greatest taxonomic resolution has been achieved using molecular data (Apakupakul et al, 1999;Martin, 2001;Siddall et al, 2001;Erséus and Källersjö, 2004;Rousset et al, 2007;Marotta et al, 2008;Struck et al, 2011;Weigert et al, 2014) and ultrastructural characters of spermatozoa (Jamieson and Rouse, 1989;Ferraguti and Erséus, 1999;Cardini and Ferraguti, 2004;Marotta and Ferraguti, 2009), although such data are not yet available for fossils, and the relationships inferred among some groups are still disputed.…”

Biological and morphological aspects ofBranchiobdella italica(Annelida: Clitellata) in a native crayfish population of central Italy

“…The systematics and ranking of this group remained a matter of debate for a long time (Holt 1986;Gelder & Brinkhurst 1990;Cardini et al 2000). However, recent molecular studies (Martin 2001;Siddall et al 2001;Erséus & Källersjö 2004) recognized branchiobdellidans as a monophyletic taxon, sister-group to Lumbriculida (McHugh 2000) within Clitellata (Gelder & Brinkhurst 1990;Gelder 1996;Gelder & Siddal 2001;Siddall et al 2001). Also using sperm morphology (Ferraguti & Erséus 1999), lumbriculids were found to be the group of oligochaetes closest to the clade including branchiobdellidans.…”