Thursday, February 14, 2013

Enigmatic Egg Masses

Wednesday was great because we got to go to TWO field sites in one day! Going into the field is by far my favorite part of marine ecology. We wanted to collect two more species of snails: Crucibullum spinosum and Bostrycapulus calyptraeformis. Here I am in the top photo and Allan in the bottom photo. We went to Chumical in Veracruz, but we didn't find anything! Maybe the snails live in patches and we just didn't look in the right spots.

Me (Gina) at Chumical at low tide.

Allan looking for C. spinosum and B. calyptraeformis at Chumical at low tide.

Recently, we have been learning about the moon snail (family Naticidae, genus Polinices) egg masses and I want to try to describe the egg masses as best as I can to try to help us determine the species we have been observing. We don't know what species it is, and we would especially want to know if we are looking at multiple species! I took some vertical trans-sections of two egg masses we found at Venado Beach on Feb 11 and also of two egg masses from Chumical on Feb 13. Between the sand grains, I was looking for egg capsules. Here's what I saw:

Moon snail  (Polinices sp.) egg mass from Feb 11, 2013, 
collected at low tide in the middle of the day. 

I think those round, shiny spherical things are the larvae. I teased the egg mass apart to get a better idea. See the next photo:

After I teased the egg mass apart, this is what I found (above). I'm pretty sure those are moon snail larvae. They look like the hatchlings we have taken pictures of after rearing the eggs in the lab. See the next photo:

Moon snail hatchlings, reared in the lab. We keep the egg masses in cups until 
they erode and larvae are released, then we preserve them for photography.

 I also looked more closely at two egg masses I collected from Chumical on Feb 13. The shape of the egg mass was a bit different than those from Venado Beach, so I thought maybe it was a different species. Below are the ones from Chumical. They seem to have a shorter central margin. I don't have pictures of the Venado Beach egg masses, but I'll try to take some soon to compare!

Egg mass #1 from Chumical, collected on Feb 13 at low tide during the afternoon.

Egg mass #2 collected at the same place and time as #1.

Here's the vertical trans-section:

I couldn't identify any egg capsules or hatchlings in these, even when I teased them apart. I'm thinking that it probably depends a lot on how old the egg mass is: older ones will have more developed larvae. So maybe this one is younger? But then where are the egg capsules with the developing embryos? I still have much to learn!

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