Gammarus pulex - ID Help Though - Video Added

[Mitch640]

And, here is a 2 and a half minute video.

http://www.youtube.com/watch?v=zri_lHAWc1g

[Cactusdave]

Where the internet fails, then older technology must be called upon. This illustration is from 'The Invertebrates', Fourth Edition by Borrowdale, Eastham, Potts and Saunders, published by the Cambridge University Press, 1963. It is of a female with egg sacs and shows I think, that the structures Mitch is refering to are indeed egg sacs.

[Mitch640]

Thanks Dave, that's a great help. There are some text descriptions that bear out this image, saying that the eggs are carried internally until they develop to a certain stage, then are kept in a pouch until they hatch. My thinking was, they were in the pouch stage.

Maybe I will get to see her again, as I put her back in my tank, still very much alive.

And speak of the devil, I can see her right now in my tank. Every morning, the first thing I do is turn on a lamp near the tank, and many of the visible bugs will come to that side of it, for the light. I can see her in there right now, catching and dining on Cyclops, one after the other. Amazing.

[Cactusdave]

Just to clarify, I assume Mitch is refering to the structures that can be seen on the lower surface of the thorax, between the very obvious coxal plates which can be seen clearly in his photos and whose relative location is shown nicely in the T.S. of thorax diagram in the 'Invertebrates' book. The area I'm refering too is called the 'pouch' in this diagram and is often heavily obscured by the coxal plates in side views. The structures referred to in the diagram as 'oostegites' which appear to clasp or support the egg sac are also visible I think in Mitch's last picture.

[Mitch640]

Just so we are talking about the same items, here are a few pointed out. There were several rows of them attached to the belly area. In Wisconsin, we call them udders.

[Cactusdave]

Yup. It would be nice to try to resolve the contents of the 'udders' a little better, but they certainly look like egg sacs to me.

[Mitch640]

Here ya go.

[NikonUser]

My interpretation.

The red arrows = gills (branchiae in the diagram).

The oostegites that fold over each other to form a pouch to hold the eggs are the 2 tube-like structures; one immediately to the left of the left arrow and one more crossing the 2 legs.

The little balls beneath the heart are the actual eggs.

I believe there there has been a little confusion between form and function. All these structures are part of the appendages (basically legs) but have been highly modified to form gills, oostegites, coxal plates.

The eggs in the diagram are the 11 small circles on the coxal plates.

[Cactusdave]

Yes that's clear now. Thanks for that explanation NikonUser. I had been fooled by the gills being labelled 'branchiae', an unfamiliar term, in the diagram.

[Mitch640]

I'm just a beginner here, but if those are gills, wouldn't all the shrimps have them, and pretty much in the same place? I ask, cause I went through all my other pics of these guys and do not see anything like these on the others. Also, in the video, these things, whatever they turn out to be, are separate from the legs, like an added object in those sections, which also have legs.

In fact, this one looks kind of skinny, slim in the belly, compared to the others. The only one that has anything similar, is this one, the first Gammarus shrimp I found. You can see, these look more like plates though, and more square.

[Mitch640]

Ah, OK, 'branchiae', I think I am beginning to see how it's put togther now. The plates in this last one are haiding the 'branchiae'.

The picture is coming together now. My first one does not have the plates though, so there is still a mystery.