Stanley A. Schultz wrote:

When the embryo casts off this membrane it is said to "hatch." The resulting creature is called a "postembryo," and I think that's equivalent to the European "nymph." Because the covering wasn't made by the embryo, this is not considered a true molt. And, the resulting stage is not considered an instar because an instar is defined as the stage AFTER A MOLT. And, the first instar follows the first molt. (And, the term "eggs with legs" is used only by enthusiasts and amateurs. It isn't part of either naming system, and the professionals don't use it. Except as a vernacularism, it has no meaning or significance.)

So if when the egg sheds off the membrane, what according to the Americans is it called if the name instar is only applied once the eggs with legs have molted into 1st instar?

T-rad wrote:

Stanley A. Schultz wrote:

Ceratogyrus wrote: When the embryo casts off this membrane it is said to "hatch." The resulting creature is called a "postembryo," and I think that's equivalent to the European "nymph." Because the covering wasn't made by the embryo, this is not considered a true molt. And, the resulting stage is not considered an instar because an instar is defined as the stage AFTER A MOLT. And, the first instar follows the first molt. (And, the term "eggs with legs" is used only by enthusiasts and amateurs. It isn't part of either naming system, and the professionals don't use it. Except as a vernacularism, it has no meaning or significance.)

So if when the egg sheds off the membrane, what according to the Americans is it called if the name instar is only applied once the eggs with legs have molted into 1st instar?

You have it right there in the quoted portion that you included. I've highlighted it for you.

Hope this helps.

Added material, for your file of 1,001 useless facts. I hope this doesn't confuse you even more.

The verb "hatch" and its derivative "hatching" are actually the vernacular terms for the process. The formal terms are "eclose" and "eclosion." Thus, while we would say, "The eggs are about to hatch" on the Internet, a scientist or scientist wannabe would say, "The eggs are about to eclose." And, while we would say, "The act of hatching is a dangerous thing" the scientist or scientist wannabe would say, "The act of eclosion is fraught with danger."

I had trouble remembering about "eclose" (Sick dog kept me up most of the night cleaning up messes.) until I found one mention of the word on Wikipedia . It's obviously a very important term. :blink:

You really needed to know that, didn't you? :woohoo:

Stanley A. Schultz wrote:
BTW, the babies in that photo are NOT second instar. They're FIRST instar.

According to the American way wouldn't the Ts in the photo be called a postembryo and only once they molt again they will be called a first instar?

Sorry this is just quite confusing... Only way to learn is to ask

Stanley A. Schultz wrote: By Downes' system (the American one), the egg is enclosed in a shell or membrane called the chorion. The chorion is produced by the mother as the initial packaging.

When the embryo casts off this membrane it is said to "hatch." The resulting creature is called a "postembryo," and I think that's equivalent to the European "nymph." Because the covering wasn't made by the embryo, this is not considered a true molt. And, the resulting stage is not considered an instar because an instar is defined as the stage AFTER A MOLT. And, the first instar follows the first molt. (And, the term "eggs with legs" is used only by enthusiasts and amateurs. It isn't part of either naming system, and the professionals don't use it. Except as a vernacularism, it has no meaning or significance.)

However, from that time onward, every time the creature casts off a covering, the covering will have been made by the creature itself (not its mother), that will be considered a molt and is appropriately numbered, and the following stage in development is called an instar and inherits the number of the molt that produced it.

Now I am even more confused?
So, according to the American method then, the spider goes like this:
Eggs -> Post-embryo (Hatching)
Post-embryo -> First instar (Moulting)
First instar -> Second instar (Moulting)
Etc.

Therefore the spiders in the pictures are Post-embryo's (American method) or eggs with legs/nymphs (European method).
Or am I missing something?

I understand it how Cerat understands it as well. Most of us use this method in South Africa, I've just not heard anyone call it a postembryo, only eggs with legs, but otherwise it looks like we follow the American method

To save a bunch of repetitive posts I'm bunching a couple of your queries together. Pay attention to the "QUOTE" leaders to keep them straight.

T-rad wrote:

Stanley A. Schultz wrote:
BTW, the babies in that photo are NOT second instar. They're FIRST instar.

According to the American way wouldn't the Ts in the photo be called a postembryo and only once they molt again they will be called a first instar? ...

See below.

T-rad wrote: ... Sorry this is just quite confusing... Only way to learn is to ask

Not really. I think you have the progression of stages right, you just are confused about which stage we're looking at in that photo. See below.

Ceratogyrus wrote: ...

Stanley A. Schultz wrote: By Downes' system (the American one), the egg is enclosed in a shell or membrane called the chorion. The chorion is produced by the mother as the initial packaging.

When the embryo casts off this membrane it is said to "hatch." The resulting creature is called a "postembryo," and I think that's equivalent to the European "nymph." Because the covering wasn't made by the embryo, this is not considered a true molt. And, the resulting stage is not considered an instar because an instar is defined as the stage AFTER A MOLT. And, the first instar follows the first molt. (And, the term "eggs with legs" is used only by enthusiasts and amateurs. It isn't part of either naming system, and the professionals don't use it. Except as a vernacularism, it has no meaning or significance.)

However, from that time onward, every time the creature casts off a covering, the covering will have been made by the creature itself (not its mother), that will be considered a molt and is appropriately numbered, and the following stage in development is called an instar and inherits the number of the molt that produced it.

Now I am even more confused?
So, according to the American method then, the spider goes like this:
Eggs -> Post-embryo (Hatching)
Post-embryo -> First instar (Moulting)
First instar -> Second instar (Moulting)
Etc.

Therefore the spiders in the pictures are Post-embryo's (American method) or eggs with legs/nymphs (European method).
Or am I missing something?

You're not crazy. You've just missed a stage.

For the record, here is a blow by blow listing of the various events in the development of a typical tarantula.

Click or Right-click the thumbnail to get a larger image. Then, click that image to get a still larger image. THEN, right-click the image and choose "Save Image As..." and file it on your computer wherever it's convenient. You can then look at it with any graphics program anytime you need it. WARNING: It's something like 260 KB in size, a slow connection nightmare.

Now, I'm going to switch species on you. I thought I had a complete set of developmental photos for Poeciltheria ornata (like the original cannibalism photo) from Ryan, but I do not. So, I have to use G. rosea photos by Tabby Norton, another photo contributor to TKG3. Thanks and a huge tip of the old hat to Tabbie for all her help as well! Without photos like Tabbie's and Ryan's, TKG3 would have been just another tarantula book. Why is this important? Because some purist may start screaming, "But, different tarantulas develop differently!" And, that would be true. Except that what we're discussing here is general enough that I don't THINK the exact species is terribly important.

Here goes.

Postembryo ("eggs with legs," "nymph"):

Note that the legs, while present are not well developed and non-functional. They can wiggle a little, but not grasp.

1st Instar:

Here the legs, while not yet fully developed, are functional. They can move and probably grasp things. Note also that the pedicel is a lot better developed, and the bristles are beginning to develop color.

2nd Instar:

Here we're actually using our legs to crawl around.

3rd Instar:

A predacious carnivore par excellence! All it needs is 5 to 15 years of steady growth.

Now, how did we KNOW for a fact that these babies were indeed at these stages of development? Unless you had a lot of familiarity with tarantula development it would be very difficult. Tabbie kept excellent records of their eclosion and molts, that's how! Yay, Tabbie!

Test next Friday!