Max Hämmerle


Muscle development in the larval stages of Pycnogonum litorale

MSc Student
Advisor: Georg Brenneis

Unit for Integrative Zoology, Department of Evolutionary Biology
University of Vienna


Pycnogonida - also called Pantopoda or sea spiders - are the sister group to all other Chelicerata (Euchelicerata) and therefore diverged near the base of the arthropod tree of life. This makes them an interesting taxon for the study of evolutionary developmental processes in the arthropod lineage. To date, investigations on pycnogonid development are scarce and in particular the development of the skeletomusculature is unknown. 

Pycnogonum litorale is especially suitable for this purpose because of its probably plesiomorphic developmental pathway not only in sea spiders but in the whole arthropod lineage, which is characterised by a free-living parasitic protonymphon larva. This is followed by subsequent anamorphic postlarval development. During this phase not only new body segments and walking legs emerge with each moult, also new podomeres in preexisting walking legs appear.  Additionally, at the end of the postlarval phase, Pycnogonum litorale undergoes a feeding host shift, from a hydrozoan to an anthozoan host, with striking changes concerning their feeding apparatus and anterior body morphology.

Using histochemical and immunohistochemical fluorescence staining methods paired with confocal laser scanning microscopy (CLSM) I aim to document and analyze the muscle development during the postlarval phase of Pycnogonum litorale, with an outlook to integrate additional methods in later stages of the study and the intend to compare my findings with similar works on other arthropod groups.