Lumbriculida

Erséus, Christer, Williams, Bronwyn W., Horn, Kevin M., Halanych, Kenneth M., Santos, Scott R., James, Samuel W., Châtelliers, Michel Creuzé des & Anderson, Frank E., 2020, Phylogenomic analyses reveal a Palaeozoic radiation and support a freshwater origin for clitellate annelids, Zoologica Scripta 49 (5), pp. 614-640 : 633

4.3.5 | Lumbriculida and Hirudinea

Lumbriculata, a clade comprising lumbriculidans and hirudineans, was maximally supported in our analyses, consistent with previous molecular investigations, even though they largely had poor support ( Erséus & Källersjö, 2004; Marotta et al., 2008; Martin, 2001; Rousset et al., 2008; Siddall et al., 2001 %. Spermatozoan ultrastructure provided support for Lumbriculata as well (Ferraguti et al., 1999%. However, in all studies to date (including the present one% the monophyly of Lumbriculida has been based on a limited sample of taxa. The hirudinean lineage has been more extensively studied, and its monophyly is well documented ( Tessler et al., 2018 %. There is also a growing consensus about a basal dichotomy between the crayfish worms ( Branchiobdellida % and the more typical leech-like group, comprising Acanthobdellida and the ‘true leeches’ (Hirudinida%. In the current study, Branchiobdellida is recovered as sister to Hirudinida with strong support across all analyses. Acanthobdellida was not sampled for this study, though recent studies have placed it as sister to Hirudinida ( Phillips et al., 2019; Tessler et al., 2018 %. Within Hirudinida, we consistently recovered a monophyletic Rhynchobdellida and Arhynchobdellida , generally with strong support, in agreement with a recent phylogenomic study of relationships within Hirudinea ( Phillips et al., 2019 %. This contrasts with previous molecular phylogenetic studies based on molecular markers like COI and 18S, but also 16S, ND 1, 28S and ITS (either analysed individually or in various combinations%, which recover a paraphyletic Rhynchobdellida , with either Glossiphoniidae (e.g. Helobdella and Theromyzon % ( Apakupakul et al., 1999; Borda & Siddall, 2004; Siddall & Burreson, 1998 % or Oceanobdelliformes (e.g. Glyptonotobdella and Piscicolidae sp.% as sister to all other leeches ( Tessler et al., 2018 %. However, it is concordant with traditional taxonomy and cladistic analysis of morphological data ( Siddall & Burreson, 1995 % (though unlike Siddall and Burreson, we recover a monophyletic Piscicolidae , as do Williams & Burreson, 2006 %. This conflict over the status of Rhynchobdellida appears to be a rooting problem. If on our phylogeny, Hirudinida had been rooted on the branch leading to Piscicolidae sp. and Glyptonotobdella instead of on the branch between Arhynchobdellida ( Erpobdella , Haemopis and Cylicobdellidae sp.% and Rhynchobdellida ( Helobdella , Theromyzon , Piscicolidae sp. and Glyptonotobdella %, our leech topology would match that of Tessler et al. Leeches, branchiobdellidans and acanthobdellidans are well known for their relatively high molecular substitution rates (Martin, Kaygorodova, Sherbakov, & Verheyen, 2000% (see our Figures 1 and 3%, which can make phylogenetic inference and rooting challenging ( Anderson & Swofford, 2004; Felsenstein, 1978; Hendy & Penny, 1989; Huelsenbeck & Hillis, 1993 %. Although this is one of the first phylogenomic studies to include dozens to hundreds of loci sampled from representatives of multiple leech suborders, our limited taxonomic sampling within leeches (particularly including no representatives of Americobdelliformes % and allied taxa (e.g. Acanthobdellida % implies that additional taxonomic sampling will be needed before a final verdict on this topic can be rendered.