Meeting Abstract
The jellyfish body plan has remained relatively unchanged over time, and it has been quite successful evolutionarily. The origin of muscle from mesoderm is a central part of the investigation into the evolution of higher order (triploblastic) animals. Triploblasts have three embryonic germ layers: the endoderm, mesoderm, and ectoderm, which develop into organs, muscle, and skin. Diploblasts, lack mesoderm, the layer thought to give rise to the skeleto-muscular system. However, phyla such as Cnidaria and Ctenophora, typically classified as diploblasts, both possess striated musculature. Within Phylum Cnidaria, Class Cubozoa includes powerful, carnivorous, swimming box jellyfish that are capable of extending and contracting their tentacles for predation and defense mechanisms. We investigated the tentacle musculature of the cubomedusae Carybdea marsupialis and Tripedalia cystophora using transmission electron microscopy in conjunction with light microscopy to further understand the composition of the musculature in these primitive animals. Cross-sections of tentacular tissue exposed endodermal layers separated from ectodermal layers by a collagenous mesogleal layer. Muscle cells border the mesoglea, but remain separate from it, suggesting these muscle cells do not arise from mesoglea.
