Tubes versus Shells – is the analogy of worm tubes and snail shells caused by molecular homology?

• Applicant: Dr. Paul Kalke
• Subject Area: Evolutionary Cell and Developmental Biology (Zoology)
• Term: since 2026
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 580775983

This project investigates whether tube formation in annelids and shell formation in mollusks are based on a homologous origin and to what extent these analogous structures have evolved independently. To address this question, three key organisms exhibiting distinct forms of biomineralization are selected: Spirorbis spirorbis (calcareous tubes, annelids), Platynereis dumerilii (mucous tubes, annelids), and Lymnea stagnalis (calcareous shells, mollusks). This combination of species enables a comprehensive comparative analysis of genetic, morphological, and developmental aspects within the proposed two-year timeframe. The project’s central focus is the generation of the transcriptome for Spirorbis spirorbis (already available for the other species), which will form the foundation for subsequent gene expression studies using Hybridisation Chain Reaction (HCR). These studies aim to analyze gene expression patterns in adult and early developmental stages during tube and shell formation. In addition, orthologous genes will be identified and analyzed across all three species to determine whether the formation of various annelid tubes and mollusk shells is based on homologous genes. Complementary to the molecular analyses, detailed morphological investigations will be conducted using immunohistochemistry, confocal laser scanning microscopy (clsm), and azan-histology. These studies will precisely define the tube- and shell-forming tissues and elucidate the extent to which shell and tube formation in mollusks and annelids are homologous or have convergently evolved. Special emphasis is placed on Spirorbis spirorbis, as this species produces mineralized tubes with stratification and composition comparable to mollusk shells. Platynereis dumerilii serves as a comparison for non-mineralized tube formation, while Lymnea stagnalis represents the complex shell formation seen in mollusks. All developmental stages of these species are either easily to collect in natural habitats or available from established laboratory cultures. The project integrates morphological, transcriptomic, and genomic approaches to unravel the evolutionary relationship between tube formation in annelids and shell formation in mollusks. The results are expected to provide insights into the evolution of biomineralization and reveal the role of conserved genetic networks and molecular mechanisms driving the development of convergent structures in these taxa. All data generated will be made publicly available through established databases to support future comparative studies.

• DFG Programme: WBP Position