Meeting Abstract
P1.44 Sunday, Jan. 4 Embryonic muscle development in direct and indirect developing marine flatworms (Platyhelminthes, Polycladida) BOLANOS, D. Marcela; LITVAITIS, Marian K.*; University of New Hampshire; University of New Hampshire m.litvaitis@unh.edu
We compared embryonic myogenesis of the direct-developing acotylean polyclad Melloplana ferruginea with that of Maritigrella crozieri, a cotylean that develops via a larval stage. Fluorescently-labeled F-actin was visualized with laser confocal microscopy at different developmental stages. Developmental stages are reported as percentages of the time from oviposition to hatching. Development was completed in 7 d for M. crozieri and 22 d for M. ferruginea. At 30% development in M. crozieri and at 15% development in M. ferruginea polygonal outlines of epithelial cells were visible on the surface of the embryo. Random myoblasts appeared in peripheral areas of the egg at 36% and 22-30% development in M. crozeri and M. ferruginea, respectively. Because large amounts of yolk accumulated in the center of developing M. ferruginea, timing of the formation of primary circular and longitudinal muscle bands was possible only for M. crozieri and occurred between 37% and 44% development. For both species, an orthogonal muscle grid was established by 45-50% development. Diagonal muscles developed in M. ferruginea at 60-71% development. Hence, juveniles hatch with the basic body-wall musculature of adults. Larvae of M. crozieri did not hatch with diagonal muscles; these muscles are acquired post-metamorphosis. Specialized musculature developed in the larval lobes of M. crozieri. Oral musculature was found to be complex and was established by 72% development for both species. Our results are comparable to the muscle differentiation reported for another indirect-developing polyclad, Imogine mcgrathi and for a direct-developing species of macrostomid flatworms. Furthermore, they provide additional support that the orthogonal muscle pattern is a symplesiomorphy of Spiralia.
