Theses

Die Leptostraca (Packard, 1879) sind ubiquitär verbreite, doch obligat marine Crustacea, die von der Arktis bis in die Antarktis, in Tiefen von 0 m bis 2.500 m vorkommen. Obgleich zeitweilig Gegenstand der Diskussion, ist die systematische Stellung dieser letzten rezenten Vertreter der Phyllocarida durch morphologische und molekularbiologische Studien als Schwestergruppe zu den Eumalacostraca gut begründet. Aufgrund dieser basalen Stellung kommt Nebalia, im Zuge der Diskussion zur Phylogenie der Malacostraca, eine besondere Bedeutung zu, da möglicherweise viele der ursprünglichen Merkmale der Gehirnarchitektur des letzten gemeinsamen Vorfahrens der „Höheren Krebse“ bewahrt wurden. Bisherige Studien zur Neuroanatomie der Leptostraca sind jedoch zum Teil inkonsistent und widersprüchlich.
Das Ziel dieser Arbeit war daher die Neuroanatomie eines Vertreters der Leptostraca aufzuklären, sowie das Grundmuster der Gehirnarchitektur der Malacostraca zu rekonstruieren. Hierzu wurden immunhistochemische und histologische Experimente gekoppelt mit Licht-, Fluoreszenz- und konfokaler Laserscann-Mikroskopie, eingesetzt. Die Gehirnarchitektur von Nebalia cf. herbstii weist neben bemerkenswerten Übereinstimmungen mit bereits untersuchten Eumalacostraca und Arthropoda, auch auffällige Unterschiede auf. Die Daten werden in einem neurophylogenetischen Kontext, unter Berücksichtigung der Neuroanatomie der Remipedia und Insecta, diskutiert.

The Anomala is a fascinating group of decapod crustaceans that comprise taxa of various body forms and habits. One group assigned to Anomala is the Paguroidea. Most of these so-called hermit crabs need gastropod shells to shelter their vulnerable, unsclerotized pleon. Concerning vision, Anomala are study objects of particular interest as in their compound eyes (and to be more precise within the optical units: the ommatidia) different designs have evolved to transmit incoming light rays onto the retina via the dioptric apparatus (hexagonal or square corneal facet and crystalline cone). Some hermit crab species have developed at least two types of superposition optics, others have retained the plesiomorphic type of apposition optic in the adult state. Moreover, compound eyes of subsocial grazers, as for instance representatives of the genera Clibanarius and Calcinus, may display macroscopic patterns of spots, bars or loops distinct in colour and contrasting against the rest of the eye. Previous studies on Mediterranean hermit crabs revealed that such distinct colour patterns correspond with a discontinuous distribution of distal reflective pigment cells among the ommatidia. Besides exploring ommatidial fine structures with the transmission electron microscope (TEM) it is the main goal of this diploma project to gather the diversity of discontinuous pigment shields in the compound eyes of indopacific hermit crabs, exemplified by two diogenid species common in mangrove swamps as well as riff lagoons: Clibanarius longitarsus and Clibanarius signatus. Light measurements are conducted in the field to describe the light regime the hermit crabs are exposed to. Behavioral observations will help to determine activity rhythms. The putative systematic importance of spotted eyes will be evaluated by using molecular sequence data.

Taxonomy, vertical distribution, biogeography and comparative sensory organ morphology of chaetognaths in epi-, meso- and bathypelagic zones of the Atlantic Ocean and the Mediterranean Sea
This diploma thesis presents the results of almost nine months of chaetognath research. These studies took place from November 2009 until August 2010. For about one month, Mrs. Dipl. Biol. Helga Kapp (Biocentre Grindel and Zoological Institute, University of Hamburg) introduced me into the anatomy and taxonomy of Chaetognatha. In addition, I was able to collaborate with Dr. Yvan Perez (Institut Méditerranéen d´Ecologie et de Paléoécologie of the Université de Provence in Marseille, France) to gain insight into the field of taxonomy and phylogeny of chaetognaths.
This diploma thesis was carried out under the supervision of Prof. Dr. Steffen Harzsch (Department Cytology and Evolutionary Biology, Zoological Institute and Museum, Ernst-Moritz-Arndt-University of Greifswald), as well as under the supervision of Prof. Dr. Stefan Richter (Department of General & Systematic Zoology, Institute for Biosciences, University of Rostock). It flanks project studies on the neurophylogeny of Chaetognatha, which are conducted by Mrs. Dipl.-Biol. Verena Rieger, who is affiliated with the working group of Prof. Harzsch in Greifswald. These project studies started in 2007 and are embedded into the research focus program “Metazoan Deep Phylogeny” (SPP 1174) funded by German Research Council (DFG). The various chaetognaths, which became study objects of this diploma thesis, will be further processed by V. Rieger with regard to neuroanatomy.

Chaetognaths are members of the marine plankton world-wide. They inhabit all zones of coastal waters and the open oceans as well as on and near the bottom, from polar to tropical regions, and at all depths. In spite of their small size (1-120 mm), they play an important role in the marine food web as the primary predators of copepods.
Chaetognaths use several sensory organs for the detection of prey. They rely on external sensory hairs to receive prey-produced vibrations of the surrounding water and are therewith enabled to locate their food. In this diploma thesis the presence or absence and moreover, the arrangement and function of ciliary fence receptors is observed using light and scanning electron microscopy as well as immunohistochemical methods.
This small group of marine animals has been used as indicator of the movements of bodies of waters for decades. These water masses have associated temperature, salinity and depth factors, which affect the distribution of the different species of chaetognaths. Within four expeditions to the Atlantic Ocean (waters off Madeira and Cape Verde, waters off the eastern South American coast) and the eastern part of the Mediterranean Sea zooplankton samples were taken. Located chaetognaths were studied in terms of biogeography and vertical distribution patterns. Species determination was performed using light and scanning electron microscopy.
Chaetognaths represent an isolated phylum, whose phylogenetic position within the bilaterians is still unsolved. Molecular phylogenetic studies using SSU RNA were carried out to help determine specimens from the Mediterranean Sea that were indeterminable by morphology. The resulting phylogram groups these specimens with Sagitta bipunctata. However it cannot be excluded that the specimens represent a new species, as the 18s RNA gene has only a slow rate of sequence evolution and does not resolve on the species level. Future Analyses with faster evolving sequences as COI should be carried out.

Birgus latro the giant robber crab or coconut crab (Anomura, Coenobitidae) is the largest land-living arthropod in the world and inhabits Indo-Pacific islands such as the Christmas Island. Several previous studies (e.g. Stensmyr et al., 2005) have provided evidence that B. latro has a fine and differentiated sense of smell. The conquest of land occurred probably five times convergently within Crustacea. In this regard, we are interested in terrestrial adaptations of the sensory organs and the nervous system of different crustacean taxa in comparison to their nearest marine relatives. Our focus is on the morphology of central olfactory processing areas. We examined histological cross sections of the brains of B. latro and three other species among the Brachyura and Anomura with immunohistochemistry against synaptic proteins and allatostatin. For these experiments, we analyzed the marine Carcinus maenas (Brachyura), Pagurus bernhardus (Anomura) and the terrestrial Gecarcoidea natalis (Brachyura). In addition, we reconstructed a three dimensional model of the brain and selected brain structures of B. latro. Our aim is to improve the knowledge of the brain and the central olfactory pathway of Crustaceans as well as a better understanding of the different adaptation strategies for conquering land within the Meiura.

The genus Spadella belongs to the Chaetognatha, a group of marine animals which are adapted to a benthic way and can be found in all seas. The newly described Spadella valsalinae sp. nov. was discovered and collected in the Northern Adriatic Sea in 10–11 m. It is closely related to Spadella cephaloptera, Spadella ledoyeri, Spadella birostrata and compared with the two interstitial species Spadella interstitialis and Spadella nunezi. In order to understand the distribution of the Spadellids, their biogeography in the Mediterranean Sea was studied with the focus on troglophilic species in the western Mediterranean Sea with a coexistence of infralitoral species in an eperic sea as the Adriatic Sea.