Spinnerets galore

[ThorsWebb]

I just recently noticed on one of my spiders that she, to my surprise, has more than one pair of spinnerets! I had no idea that any species had more than one pair. (Yes, it's ok to laugh at my ignorance )

I find this to be very interesting, so I try to read more, what they are for and how many pairs of spinnerets can a spider have. I was able to find some reasonable detail information (e.g. Liphistius has four pairs of spinnerets!) and some of the different use for different pairs.

My questions, that I could not find the answer for is: do all Theraphosidae have two pairs of spinnerets? As I understand from what I read, one pair with the male is for making the spermweb, but what do the female use, if functional at all, the second pair to?
Is having two pairs of spinnerets a defining characteristic with Theraphosidae?

 

[AphonopelmaTX]

do all Theraphosidae have two pairs of spinnerets? As I understand from what I read, one pair with the male is for making the spermweb, but what do the female use, if functional at all, the second pair to?
Is having two pairs of spinnerets a defining characteristic with Theraphosidae?

1. Yes, all theraphosid spiders have two pairs of spinnerets.
2. Males have an additional set of silk spigots right above the epigastric furrow called epiandrous fussilae. It is with these silk spigots that a male will use to reinforce a portion of a sperm web to deposit a sperm packet on. The bulk of the sperm web is constructed with the regular spinnerets on the abdomen. Both pairs on males and females are functional.
3. No, two pairs of spinnerets by itself is not a diagnostic family character for Theraphosidae. All spiders in the infraorder Mygalomorphae have two pairs. What is diagnostic for Theraphosidae regarding the spinnerets is that the tips of the long pair are finger-like in shape. Other mygale families have a different shape.

Also, something I would like to point out about the spinnerets, even if it maybe obvious, is that the silk comes from the hairs covering the appendages, called silk spigots, and not the appendages themselves. This relates to answer number 2 above where in males, silk spigots appear above the epigastric furrow and on the spinnerets.

 

[Vanessa]

Also, all four spinnerets can work in tandem, or independently of each other.

 

[AphonopelmaTX]

Also, all four spinnerets can work in tandem, or independently of each other.

Wow, those are great pictures! The second one looks like it should be included in a textbook. Ever try to get a picture of a male using the epiandrous fussilae?

 

[Vanessa]

Wow, those are great pictures! The second one looks like it should be included in a textbook. Ever try to get a picture of a male using the epiandrous fussilae?

Thanks.
Despite having as many mature males as I have, I have only caught two making them. In both cases, they were arboreal species and I could barely see them, let alone get a decent photo. Maybe one day.

 

[ThorsWebb]

Thank you, AphonopelmaTX, for a very informative and nice reply. I really appreciate your answer a lot! It's difficult to find good information online, I'm new to the world of spiders so I'm not familiar with all the expressions plus, English is not my native language.
You explain in a very good way.

Thank you VanessaS! Your pictures are true art! Absolutely amazing! Truly stunning!

I only have those (see picture) options for "rating" available. Don't know why that is.
Sorry if my ratings don't reflect my appreciation.