MARTINEZ, G.M.: Early Emergence of contractile competence in mantle and funnel muscles in embryonic squid.

F-actin filaments appear early in the development of the squid embryo. They emerge in a random and diffuse pattern during the appearance of organ primordia and become more widely distributed and organized as development continues. My data suggest that F-actin filaments present in early embryonic development are not merely structural; rather they may be functional and contractile surprisingly early. Moreover, as development proceeds, embryos demonstrate an increasing ability to contract certain muscles, primarily the mantle, a behavior which has been observed earlier than has been documented in the literature. In order to determine at which stage muscles are sufficiently organized for effective mantle and funnel function, I prepared a complete developmental series of squid embryos, from gastrulation to hatching, with phalloidin, a flourescent stain that binds specifically to F-actin. Embryos from Arnold stages 20 to hatching were also dechorionated and filmed to observe movements suggestive of respiration and potential locomotion.