Developing imaging techniques for studying brachyuran crab zoeae and adult morphology of gonopods with an emphasis on the invasive Chinese mitten crab, Eriocheir sinensis

ABSTRACT
In the present study, the zoeal stages of the Chinese mitten crab, Eriocheir sinensis H. Milne Edwards, 1853, which is now well established in the Thames catchment and other watersheds around the UK, were examined as a case study. Traditional illustration techniques such as line drawings were rejected, instead zoeal images were visualised using a modern-day technique; namely Confocal Laser Scanning Microscopy. A protocol was established to re-describe the zoeal stages of this invasive species. A number of steps were considered and trialled including pre-processing of zoea comprising cleaning, staining, digesting, dissecting and mounting; the scanning of zoeal mouthpart etc. using a Nikon A1-Si confocal laser microscope and the post-processing of data by applying open-source, freeware programs ImageJ and Drishti to visualise the larval appendages. This study also investigated the brood potential of ovigerous mitten crabs collected from the Thames Estuary and held in the laboratory for observation. And lastly, the various techniques used to study the zoeal stages were applied in an investigation to scan the first male gonopod of a number of brachyuran crab species. The male gonopod is a species diagnostic character, the distal morphology of which can be extremely complex and difficult to draw. The results of this work confirmed that a second species of mitten crab, not Eriocheir sinensis, is present on the European mainland, it verified the existence of an undescribed species of Libystes A. Milne Edwards, 1867 from the Red Sea and proved the true identity of Monomia argentata A. Milne-Edwards, 1861 from an old specimen held in the dried collections of the Natural History Museum, London.