Tuesday, August 14, 2012

Chris - Week 7: Final Scans and Project Summary

During Week 7, I concluded my project by examining two additional age groups with the scanning electron microscope. This time, I looked at 25 hour old and 36 hour old cohorts. My goals were to create cleaner specimens to scan (particularly with the 25 hr) and to observe any intermediate characteristics in the 36 hr group.

I was only partially successful. I avoided the globular objects that plagued my previous scans, only to find larger geometric objects. While interesting, they are just as vexing as the debris from last week. For whatever reason, these crystals were only present on the 36 hour specimens. On a more positive note, the 25 hour old group was very revealing, and the 36 hr group was more similar to the 48 hr than I would have guessed.

Figure 1: Posterior view of a 25 hour old
M. alaskensis larva
Figure 2: Angled anterior view of a 25 hour
old M. alaskensis larva

In Figure 1, note the indentation in the center of the specimen. This will continue to invaginate as the larva transitions to a pilidium, forming the esophagus and gut through the process known as gastrulation. Figure 2 shows that the apical organ is already forming at 25 hours. It is not clear from this image if the apical tuft is also present.

The specimen shown below in Figure 3 is covered with relatively large, geometric objects that have not been identified. Figure 4 shows the apical organ, which is rarely seen in this detail (cilia normally obscure it). Also note the relatively well developed apical tuft. Both specimens appear more similar to the 48 hour age group than they do to the 25 hour.

Figure 4: Angled anterior view of a 36 hour
old M. alaskensis larva
Figure 3: Posterior view of a 36 hour old
M. alaskensis larva

So that pretty much concludes the data collection phase of my project. I have examined M. alaskensis larvae from between 10 hour and 3 weeks of age over the course of this summer, utilizing both confocal and scanning electron microscopy. Now in the final week, I have to organize this large collection of micrographs and observations into a coherent and at least mildly interesting presentation. Wish me luck! 

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