Data from: Illuminating the base of the annelid tree using transcriptomics

Annelida is one of three animal groups possessing segmentation and is
central in considerations about the evolution of different character
traits. It has even been proposed that the bilaterian ancestor resembled
an annelid. However, a robust phylogeny of Annelida, especially with
respect to the basal relationships, has been lacking. Our study based on
transcriptomic data comprising 68,750 – 170,497 amino acid sites from 305
– 622 proteins resolves annelid relationships, including Chaetopteridae,
Amphinomidae, Sipuncula, Oweniidae, Magelonidae in the basal part of the
tree. Myzostomida, which have been indicated to belong to the basal
radiation as well, are now found deeply nested within Annelida as sister
group to Errantia in most analyses. Based on our reconstruction of a
robust annelid phylogeny, we show that the basal branching taxa include a
huge variety of life-styles such as tube-dwelling and deposit-feeding,
endobenthic and burrowing, tubicolous and filter-feeding, as well as
errant and carnivorous forms. Ancestral character state reconstruction
suggests that the ancestral annelid possessed a pair of either sensory or
grooved palps, bicellular eyes, biramous parapodia bearing simple chaeta
and lacked nuchal organs. Since the oldest fossil of Annelida is reported
for Sipuncula (520 Mya), we infer that the early diversification of
annelids took place at least in the Lower Cambrian.