P1.97 Wednesday, Jan. 4 Pelvic limb morphology in the lungfish Protopterus annectens KING, Heather M*; HALE, Melina E; Univ. of Chicago; Univ. of Chicago firstname.lastname@example.org
The lungfish Protopterus annectens is a benthic pelvic fin biped. Its long, slender pelvic fins are capable of a wide range of movements, and in particular are used during locomotion for substrate contact and propulsion. While it has been shown that the pelvic fins in P. annectens are composed of small, serially homologous skeletal elements, the arrangement and orientation of the muscles relative to the skeleton and how this morphology relates to the wide range of movement of the fin is unknown. Here we used histological methods to reconstruct a segment of the pelvic fins in P. annectens. The fins consist of a cartilaginous skeleton with serially repeating elements; between consecutive elements is a pad of soft connective tissue. Connective tissue sheets ran along the long axis of the fin from proximal to distal at an angle of approximately 15o relative to the medial skeleton, and were continuous around the circumference of the fin, in a cone shape. Each cone of connective tissue extends approximately two cartilage segments, originating at the skin distally and inserting on or near the joints between the cartilage segments. Between adjacent layers of connective tissue was a layer of muscle with varying fiber angles. Muscle is distributed around the skeleton and down the length of the fin. The muscles are not divided into discrete groups corresponding to the dorsoventral plane or adductor abductor regions, but appear to be radially arranged. We hypothesize that this cone-shaped arrangement of muscle, integrated with the skeletal elements and skin, provides bending and may also stiffen the fin, allowing for the complex movements observed during locomotion.