Body size evolution in Priapulida – ancestrally or secondarily small?

• Applicant: Professor Dr. Andreas Schmidt-Rhaesa
• Subject Area: Systematics and Morphology (Zoology) ; Evolution, Anthropology ; Evolutionary Cell and Developmental Biology (Zoology)
• Term: from 2020 to 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 454319699

• Final Report Year: 2024

Final Report Abstract

To answer the question, whether microscopically small or large (in the cm range) body size is ancestral for Priapulida, we collected morphological and molecular data from several specimens. With 22 known species, Priapulida are a small taxon, but include large and small species with a variety of morphological characters and reproductive biology. The macroscopic species Priapulus caudatus, P. tuberculatospinosus, Priapulopsis australis, P. bicaudatus, Halicryptus spinuolsus and H. higginsi were investigated morphologically in detail. This led to a better comparison and understanding of characters, especially of the pharyngeal teeth, introvert scalids and different receptive structures on the body. CO1 sequences revealed that the small species H. spinulosus has a circumpolar distribution, whereas the large congeneric species H. higginsi has a locally strongly restricted occurrence. Phylogenomic analyses based on transcriptomes and genome skimming data showed that the microscopically small genera Meiopriapulus and Tubiluchus branch off first and sequentially, making it likely that small body size is ancestral for Priapulida.

Publications

• Morphology of larval and postlarval stages of Priapulopsis bicaudatus (Danielssen, 1869) (Priapulida) from the north atlantic ocean. Zoologischer Anzeiger, 302, 1-16.
  Schmidt-Rhaesa, Andreas & Raeker, Jan
  
• David versus Goliath: An interspecific comparison between small-sized Halicryptus spinulosus and large-sized Halicryptus higginsi (Priapulida). Zoologischer Anzeiger, 313, 1-20.
  Raeker, Jan; Worsaae, Katrine & Schmidt-Rhaesa, Andreas
  
• New morphological structures of Priapulus caudatus, Lamarck 1816 (Priapulida) and analysis of homologous characters across macroscopic priapulids. Zoologischer Anzeiger, 312, 135-152.
  Raeker, Jan; Worsaae, Katrine & Schmidt-Rhaesa, Andreas
  
• Review of the Priapulida of New Zealand with the description of a new species. New Zealand Journal of Zoology, 52(3), 274-308.
  Schmidt‐Rhaesa, Andreas & Raeker, Jan