The Origins of Neurons and use of Glutamatergic Signaling in the Ctenophore: Pleurobrachia bachei
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Ctnenophores are a group of marine, jelly like, comb bearing metazoans. This phylum consists of an estimated 100-‐200 species (Mills CE, 2012). Ctenophores are similar to cnidarians in that they have a homologous mesoderm consisting of a jelly like substance called mesoglea. They differ in that they do not have venomous stinging nematocysts but instead have numerous sticky colloblasts lining the tentacles. They also differ in locomotion, cnidarians typically use a contracting pulse of the bell to propel themselves, whereas, ctenophores use 8 rows of ctene plates that paddle the animal through the water. It is believed that they have true striated muscle and a primitive central nervous system (CNS) consisting of the aboral organ and polar fields. The Aboral organ is composed of a balancing statocyst that is attached to all ctene rows by a series of balancers and ciliated furrows. Signaling occurs from the aboral organ to the ctene rows. Each row is capable of beating separately from any of the others, indicating a complex signaling. Extending from this CNS are two nerve nets. One nerve net is located in the ectoderm while the other extends through the mesodermal mesoglea. Genetic data and morphology are both used in comparing basal metazoans and determining evolutionary ancestors.