Regeneration in bipinnaria II

In May I surgically bisected several bipinnaria larvae of the starfish Pisaster ochraceous. I made the cuts across the esophagus (anterior to the coeloms), separating the preoral lobe and the mouth from the rest of the larva (see pictures). I wanted to see if the fragments would indeed regenerate, as described in the literature.

The anterior and posterior fragments were cultured together and observed 13 days post-surgery. I observed two distinct morphotypes in the culturing vessel representing the anterior and posterior fragments. The first photo shows one of the posterior fragments 13 days after bisection. You can see that these fragments healed and regenerated the preoral lobe and the mouth. The fragments that I interpreted as being anterior, healed, but did not appear to regenerate 13 days after bisection (see bottom picture). This is surprising because bipinnaria larvae of the same species are apparently capable of regenerating their anterior ends under similar experimental conditions (Vickery et. al. 2002). I continued to monitor these fragments for several more weeks to see if the anterior ends would finally regenerate. As of six weeks post-surgery, I found two (out of original 15) anterior fragments that did not appear to regenerate.

Vickery, M. S., Vickery, M. C. L., McClintock, J. B. 2002. Morphogenesis and Organogenesis in the Regenerating Planktotrophic Larvae of Asteroids and Echinoids. Biol. Bull. 203: 121–133