MARTINEZ, G.M.; University of New Hampshire: Ultrastructural development and differentiation of the mantle musculature in embryonic squid

The muscular mantle of squids has two primary functions:locomotion and respiration. The capacity of the mantle to execute these dual functions is due to the presence of two distinct muscle fiber types that are functionally and metabolically analogous to vertebrate red and white muscle fibers. The different muscle fiber types are easily distinguishable from each other based on their distribution in the mantle and by their mitochondrial content. The two fiber types are divided into three distinct layers. The muscle fiber types used for slow jetting, hovering and respiration are located immediately beneath the inner and outer tunics. Sandwiched between the two layers of superficial fibers is a layer of glycolitic fibers used for fast and escape jetting.The physiology and ultrastructure of the two muscle fiber types have been extensively studied in adult squids and to some extent in juveniles. Their roles in respiration and locomotion have been clearly identified metabolically, functionally and electro-physiologically. However, little is known about the development and differentiation of muscle cells in general and the different muscle fiber types specifically in the pre hatching stages. The present study focuses on the development and differentiation of muscle cells in the mantle of embryonic Loligo pealeii in order to investigate the spatial organization and arrangement of muscle fibers, and when the different fiber types become distinguishable from one another at the ultrastructural level. My results indicate that the superficial mitochondrial rich muscle fiber types differentiate and become morphologically distinct earlier than the central zone muscle fiber types. Both fiber types are differentiated and distinguishable from each other by hatching.