Chris - Week 6: SEM and Early Pilidia

During Week 6, I examined three new age cohorts; 21 hours old, 27 hours old, and 48 hours old. I used both confocal and scanning electron microscopy, in part to compare the results produced by the different techniques. I found that the 21 and 27 hour age groups were remarkably similar to the 15 hour cohort, both in shape and cilia distribution. The 48 hour age group was much different however, taking on the form of a pilidium rather than a disc.

 Unfortunately, this week was also fraught with difficulties. The confocal staining did not go as expected, producing results that are not worth sharing. I had better luck with the SEM specimens, although I did run into some problems with them as well. Some of the specimens, and all of the 27 hour, were covered in many small globular structures that we can't identify. Needless to say, such filthy specimens do not make for good images (at least not when the objects cover the structures being examined, i.e. cilia). 

Figure 1: A posterior view of a 21 hour
old M. alaskensis larva



Figure 2: An angled side view of a 21 hour
old M. alaskensis larva

 In Figures 1 and 2, note the somewhat "domed" shape of the specimens, as well as the patchy distribution of cilia. Figure 3 below shows the now characteristic bald patch, where Figure 4 shows that even the anterior portion is not completely ciliated after 27 hours. Svetlana believes that many of the bald patches seen so far in the 12.5 - 48 hour stages are centers for cell division, and thus larval growth. Only cells that are either mono-ciliated or are not ciliated at all can divide and reproduce; multi-ciliated cell are incapable of dividing. Also note the many globular objects covering the specimens. Their origin is unknown.

Figure 4: An anterior view of a 27 hour
old M. alaskensis larva



Figure 3: A posterior view of a 27 hour
old M. alaskensis larva




Figure 6: A posterior view of a 48 hour old
M. alaskensis pilidium


  

Figure 5: A side view of a 48 hour old
M. alaskensis pilidium




















 

Figure 7: An anterior view of a 48 hour
old M. alaskensis pilidium 






The specimen of Figure 5 displays the characteristic shape (albeit developmentally early) of a pilidium. Note the beginnings of a ciliary bands along the posterior, of which Figure 6 shows in more detail. Figure 7 shows the apical tuft of the pilidium, which is the bundle of long cilia at the anterior-most portion of the specimen.