Body size evolution in Priapulida – ancestrally or secondarily small?

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We are interested in changes of body size during evolution. The taxon Priapulida is ideal to investigate changes of body size, as among the only 21 described species are microscopic (2-3 mm) and macroscopic (several cm, up to 40 cm) species. With the ultimate goal to investigate genetic changes and drivers of evolutionary body size changes, we propose in this project to work out a robust phylogeny and compare morphological changes during ontogeny and between microscopic and macroscopic species. For a phylogeny (work package 1) we want to sequence transcriptomes of six species from the genera Priapulus, Priapulopsis, Halicryptus and Tubiluchus and complement these with data from other working groups on further species and genera (Meiopriapulus, Maccabeus). In three further work packages we will compare different organs (body cavity, musculature, cuticle, excretory organs, gonads) with different techniques (µCT, semithin and histological sectioning, phalloidin staining, tubulin staining). The work packages include comparison through the entire development of Priapulus caudatus, comparison between small (Tubiluchus) and large (Priapulus) species and intrageneric comparison of small (Halicryptus spinulosus) and large (H. higginsi) species.