Pycnogonid biology and evolution

 Sea spider evolutionary developmental biology

In contrast to terrestrial chelicerates, most sea spiders have an indirect development, i.e., they hatch as a small, segment-poor larva that undergoes a series of anamorphic molts until the adult body plan is attained. In the light of the likewise indirect development of other primary aquatic mandibulate lineages (i.e., numerous crustacean taxa) as well as fossil evidence, this type of development is suggested to be plesiomorphic for arthropods. Hence, we aim for a detailed understanding of sea spider development and seek to identify ancestral features of arthropod development by comparison to other lineages. For this purpose, we have established a stably reproducing laboratory culture of the sea spider Pycnogonum litorale.

 Sea spider regeneration

Contradicting the long-held view that arthropods and other molting animals are unable to regenerate structures of their primary body axis, we have recently discovered that juvenile sea spiders can regrow their posterior body pole and almost complete body segments after experimental amputation. To characterize the cell types and molecular mechanisms underlying this arthropod-wise exceptional ability, we now aim to combine the study of gene expression patterns with in vivo cell proliferation markers, as well as single cell transcriptomics during regeneration in our laboratory animal P. litorale.

 Sea spider neuroanatomy and arthropod nervous system evolution

Another research avenue focuses on the arthropod nervous system and its evolution. In this context, we are investigating different aspects of neurogenesis, neural differentiation and neuroarchitecture in sea spiders and other chelicerates. Given the interesting phylogenetic position of pycnogonids, this holds the potential to identify plesiomorphic traits of the chelicerate nervous system and to shed light on its transformations during early chelicerate evolution.

 Sea spider taxonomy and phylogeny

With about 1400 described species, extant pycnogonids are less speciose than many other arthropod groups. However, new species continue to be discovered on a regular basis and modern integrative studies indicate that traditional taxonomic accounts significantly underestimate real sea spider diversity. In addition to these taxonomic uncertainties, also the phylogeny of the major sea spider lineages ("families") remains contested and traditionally used external morphological traits, such as the presence and structure of the three anterior "head" appendage pairs, are now widely recognized to be highly homoplastic. Accordingly, we aim to generate new "family-wide" datasets (external morphology, internal anatomy and molecular) that help to overcome these taxonomic and phylogenetic ambiguities.

 Study & research opportunities

Interested in doing an internship, academic thesis or posdoc in pycnogonid biology? Please contact Georg Brenneis.