\cite{Goodey_2009}
Introduction
Batoids comprise more than 50% of the chondrichthyan species, and their morphological differences from other chondrichthyans beg many questions about their evolutionary history, which has only recently began to be researched in earnest \cite{Aschliman_2012}. The most striking feature of the batoid group is their enlarged pectoral fins, which in some batoid taxa such as stingrays and rajiformes is used for powering movement. However in other batoid taxa, such as Pristoidei, as well as the batoid sister group, sharks locomotion is powered with body movement combined with their caudal fin. The feature of this investigation, Raja clavata (the thornback ray), like most skates, moves through the ocean using rajiform locomotion, which is a technique of precise pectoral fin undulation to produce waves. This technique, which is unique to the Batoidea superorder, requires large specialised pectoral fins that extend the length of the thornback ray's body, and are fused to the head. Morphological evaluation of the batoid group has shown that the type of movement exhibited by individuals can be accurately determined by their pectoral fin aspect ratio, with rajiform locomotion requiring a lower aspect ratio of fin, corresponding with a higher number of waves per fin. Further study has also shown that rajiform locomotion is a While the kinematics of this type of locomotion is starting to be understood
The species being examined in this investigation is the thornback ray, otherwise known as the Maiden ray (Raja clavata), which is a skate usually located in coastal waters stretching from Morocco to Iceland, but has been sighted as far as Sri Lanka \cite{CHEVOLOT_2006}. One of the most common skates in the world, Raja clavata is carnivorous and usually eats bottom feeding crustaceans on the ocean floor, but adults have been known to prey on small fish. Tagging of individuals in the North Sea has suggested that juvenile Raja clavata don't move that much in their live, and usually stay within a 5 miles radius of where they were born, while adult individuals move between shallower coastal waters in the summer, and out to deeper waters in the winter.
To learn more about the specialised musculature and skeletal body plan that makes this type of movement possible, we skinned and skeletonised a thornback ray specimen, as well as skinning a shark comparator to examine the differences particularly in the pectoral fins that allow Rajiformes to perform pectoral undulation.
Materials & methods
Over the course of 4 days, we examined 2 thornback ray specimens (one whole specimen and the pectoral fins of another specimen for cross sections) and 1 whole Mustelus specimen (which due to morphological ambiguity was unable to be identified to species level). All specimens were provided frozen by Imperial College London, and were defrosted for 2 hours before initial dissection. Skeletonisation was performed on the ray by removing as much flesh from the skeleton as possible before allowing the specimen to soak in 40°C water for 5 minutes, before removing more flesh. This process was repeated until sufficient flesh had been removed. The specimens were refrigerated at 6°C in sealed plastic bags when not in use.
Description(or Results)
Initial dissection began on the thornback ray, with an incision about 2cm anterior of the cloaca, working in the anterior direction for approximately 5cms. This location was chosen for initial incision due to its location adjacent to the pectoral and pelvic fin. Skin was then removed, working laterally to expose the metapterygium, and our first look at the extended abductor superficialis (pictured in Fig.1). Initially it appears like the posterior region of the abductor superficialis originates from the metapterygium.The skin was then further worked off, working in the anterior direction. From this we can begin to see the origins of the