Polychaeta, Annelida, and Articulata are not monophyletic: articulating the Metameria (Metazoa, Coelomata)

Abstract

Polychaetes are metameric worms recognized for having parapodia, chaetae, and nuchal organs. Some authors have extended the Annelida to include Pogonophora, Echiura, and Clitellata. These suggestions are insufficient to generate a monophyletic group. They do not take into account two very large and important clades that in a cladistic analysis at a higher level are shown to be nested within the Annelida: the Ecdysozoa (arthropods and related taxa) and Enterocoela (deuterostomes and related taxa). Evolutionary histories of most characters across metazoan phyla are still very poorly known. Metameres and coeloms have been considered homoplastic in the literature, and yet the homeobox genes responsible for the expression of metamerism and of paired appendages, at least, are very largely distributed among the Metazoa. A phylogenetic analysis was performed for the ingroups of Polychaeta, including Clitellata, Enterocoela, and Ecdysozoa as terminal taxa. The remaining non-metameric phyla Platyhelminthes, Nemertea, Mollusca, and Sipuncula were included to root the tree within the Bilateria. Empirical data was obtained from the literature and run with the software Hennig86 with two comparative interpretations of a priori hypotheses of primary homology: one with negative characters (coding losses) and another considering only positive characters (without assumptions about losses). The most relevant conclusions are: (1) Annelida and Polychaeta are non-monophyletic, even when including Echiura, Clitellata, and Pogonophora; (2) Articulata, as traditionally circumscribed for Annelida and Arthropoda, is also not monophyletic; (3) Metameria becomes monophyletic only when Ecdysozoa and Enterocoela are included in addition to the traditional annelid taxa; (4) Ecdysozoa are the sister group of Aphrodita; (5) Clitellata are related to deposit-feeding sedentary polychaetes (scolecids), and Questidae represent their sister group; (6) Owenia plus Enterocoela form a monophyletic group related to the tubicolous polychaetes

Pogonophora (Annelida): form and function

“…On the other hand, Salvini-Plawen (2000) argues that the present state of knowledge is insufficient and that we need more detailed investigation before reaching any conclusion about the origin of Pogonophora. Almeida et al (2003) place Pogonophora in the Enterocoela, which they regard as a transitional taxon between protostomes and deuterostomes.…”

LifeWatchGreece: Research infrastructure (ESFRI) for biodiversity data and data observatories

“…Reported from Greece by Koulouri et al (2015). In the Mediterranean also reported from Spain (Desbruyères et al 1973) and Turkey (Çınar et al 2014). Çınar (2005) reports morphological differences in chaetal features between specimens from Cyprus and the original description of Kirkegaardia tesselata, concluding that the material might belong to an undescribed species.…”

“…Rouse and Pleijel 2001, de Oliveira Almeida et al 2003, Weigert and Bleidorn 2016 and the higher classification of Annelida has been in a constant flux over the last years (e.g. Zrzavý et al 2001, Helm et al 2012, Weigert and Bleidorn 2016.…”

Morphology and biology ofLaetmonice producta productaGrube (Polychaeta: Aphroditidae) in the Bellingshausen Sea and Antarctic Peninsula (Southern Ocean, Antarctica)

“…Hutchings and McRae (1993) state that this protective felt is made up by the capillary chaetae (type 6) tuft; in L. p. producta these chaetae form a lateralventral tuft of short chaetae (#4 in Figure 2a) and therefore presumably without this function. This may suggest that the spinning glands (used in the elaboration of the tubes in Acoetidae) and capillary chaetae (used in the elaboration of the dorsal felt in Aphroditidae) are non-homologous structures as suggested by Almeida et al (2003) and both persist in the parapodia of Laetmonice but without their original function, i.e. the passive protection of the body.…”