Polychaeta

Weigert, Anne & Bleidorn, Christoph, 2016, Current status of annelid phylogeny, Organisms Diversity & Evolution (New York, N. Y.) 16 (2), pp. 345-362 : 346

Polychaeta

The Polychaeta or bristle worms comprise most of the diversity of annelids. They mostly live in marine habitats and are characterized by parapodia-bearing chitinous chaetae, and were first separated from clitellate annelids by Grube (1850). The most widely used system of polychaete classification during the twentieth century was the division into two groups, mainly based on the observed lifestyle and feeding strategies ( Quatrefages 1865; Fauvel 1923): Errantia , uniting the more or less free moving and predatory forms, and Sedentaria , comprising the often sessile and tube-dwelling forms. This classification did not intend to depict evolutionary relationships and was replaced by the first thorough morphological cladistic analysis by Rouse and Fauchald (1997), who subdivided Polychaeta into two separate taxonomic clades: Palpata and Scolecida ( Fig. 1 ). The Palpata were characterized by the possession of palps and were further subdivided into two distinct groups: Canalipalpata , which feature the presence of peristomial grooved palps and include mainly burrowing deposit feeders or sessile tube dwelling filter feeders ( Sabellida , Spionida , Terebellida ), and Aciculata, which are characterized by the presence of aciculae (internalized supporting chaetae) and include members with a more mobile life style, actively foraging and predating ( Eunicida , Phyllodocida ). The Aciculata resembled more or less the Errantia adapted by Fauvel (1923). The Scolecida completely lack palps and head appendages and include mostly burrowing and deposit feeding taxa, as, e.g., Orbiniidae , Arenicolidae , or Opheliidae . A group of difficult to place polychaete worms were the B Archiannelida^. They comprise a number of interstitial worms, which are characterized by the lack of body or head appendages, which is regarded as an adaptation to the interstitium ( Hermans 1969). Formerly, they were considered as a monophyletic group within Annelida, either as part of Polychaeta or forming the basal radiation of annelids, or even their own phylum, and included five families: Dinophilidae , Nerillidae , Polygordiidae , Protodrilidae , and Saccocirridae ( Westheide 2008) . However, during the twentieth century this hypothesis of a common ancestor of the interstitial annelids remained controversial. Consequently the B Archiannelida^ were regarded as an artificial grouping with an independent adaptation to the interstitium of several members leading to a simplified body plan either by miniaturization or progenetic evolution ( Fauchald 1977; Purschke and Jouin 1988).

Figures

Fig. 1 Annelid phylogeny according to Rouse and Fauchald (1997) based on morphology. Annelida are split into Polychaeta and Clitellata. Polychaeta com- prise Palpata (Canalipalpata and Aciculata) and Scolecida