Rhombonotus gracilis

Graceful Ant Mimic at Melba, ACT

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Identification history

Rhombonotus gracilis	3 Jan 2023	Bron
Rhombonotus gracilis	1 Oct 2022	YumiCallaway
Judalana lutea	6 Jun 2020	MichaelMulvaney
Unidentified	29 Apr 2020	Bron

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User's notes

Judalana lutea?

12 comments

YumiCallaway wrote:

8 May 2020

I haven't looked into it much yet, but I would suggest one of the 4 (I think?) ant mimic genus or if not, a genus like Domoetas. These are the only ones I can think of off the top of my head with this distinctive body shape.

CathB wrote:

9 May 2020

What about Rhombonotus gracilis?

MichaelMulvaney wrote:

9 May 2020

I think it is to large to be Rhombonotus gracilis which get up to 3mm

YumiCallaway wrote:

9 May 2020

I've looked through photos Whyte & Anderson's guide (2017) and arachne.org and have come up with this list:
Not Poecilipta sp (lack of speckled head)
Not Bianor sp (very different abdomen shape)
Perhaps Damoetas sp (potentially too small)
Not Holoplatys sp (It's quite convex; it's not flat)
Perhaps Judalana sp (potentially too small)
Perhaps Ligonipes sp (difficult to tell if the brushes of hair are present on leg 1, however I think this is likely)
Not Myrmarachne sp (leg 1 is not enlarged)
Not Rhombonotus sp (too small - it's small size is specifically stated)
Not Amyciaea sp (very different)
Maybe this will help!

YumiCallaway wrote:

9 May 2020

Also, Bron, do you remember if the first pair of legs were fringed? This might help point out genus.

Bron wrote:

9 May 2020

When I took the photo, Judalana lutea was suggested by the owner of the Amateur Entomology Australia site. I think the front legs were hairy? Yumi although I'm not sure (8 yeas ago) and my photographic skills on a small subject were pretty poor. Thanks for looking so hard for the id :) IT's not Holoplatys sp. The tags I have on this photo suggested Ligonipes sp.

YumiCallaway wrote:

10 May 2020

Thanks Bron! I've taken a closer look today think J. lutea is most likely. 1. Fringes of hair on the tibia suggest Jodalana sp or Ligonipes sp with Ligonipes sp being more prominent. This would rule out Damoetas sp. 2. The length of the metatarsus + tarsus suggest Jodalana sp or Damoetas sp. I've noticed that this is quite long and thin on Ligonipes which doesn't stand out to me for this individual. 3. Colour ratio and distribution can vary for Jodalana lutea from a portion of the upper abdomen being yellow to the entire abdomen being yellow. I think it can vary on the legs too.

Bron wrote:

10 May 2020

Your close looks are excellent Yumi! I agree :) Judalana lutea isn't included in CNM though... So what next?

MichaelMulvaney wrote:

10 May 2020

We can add it when the system is fully operational

Thanks Yumi

YumiCallaway wrote:

1 Oct 2022

Good evening all 😊. I am reviewing some ID and I'd like to propose another look at this sighting and the two proceeding J. lutea sightings on CNM. This one has been on my mind ever since our discussion as I remember it being difficult with lots of possibilities and suggestions. I have a little more experience and practice since then, and we may have fresh ideas now, or new minds who have joined us since! I will explain my observations, and I would love to hear everyone's thoughts!
I think it is worthwhile to re-evaluate between Judalana lutea (p. 256 for Whyte & Anderson, 2017) and Rhombonotus gracilis (p. 298 in W. & A., 2017) as Cath had initially suggested.
Initially, R. gracilis was deemed to be too small with the 3mm maximum size mentioned. However, even in the identified spiders in the 2017 edition from Whyte and Anderson, the female was given to be 5mm and the male 4mm — both of which are larger than this limit we considered. This sightings size is recorded as 5mm to 12mm which overlaps with the species size range.

Next, for colouration and physical features. Colouration does apear to vary between individuals in J. lutea, so this colour could be within the diversity expected of the species. Looking at R. gracilis however, the colouration already matches sample photos of slightly yellowed brown (to my eyes :)), being more likely.
In 2020, we mentioned the fringes on the legs which we weren't sure of—both species have somewhat "hairy" front legs and can have fringing. So this wouldn't be a reliable determinant for this comparison 😊.
For the top of the carapace (head), this sighting seems to have dense hairs visible to us, especially in the second photo. This matches R. gracilis, whereas J. lutea seems to have sparse or little hairs that are visibly apparent in the same area.
We could also compare the abdomen shape, where J. lutea is quite slim and uniform in width, while R. gracilis appears to have a slight but apparent bulge after their patch of colour. Do you see a slight bulge? (There seems to be in the 1st photo for me)
Mostly, it is the side of the abdomen that I would like to draw attention to. Close to where the colour transitions from light to dark on the abdomen, we can see a strip of white on each side. This line doesn't seem to go around, disappearing on the top and only visible on the sides. This feature is clearly one displayed by R. gracilis (Whyte & Anderson, 2017, top of p.298 reference photos), where it appears to be absent in J. lutea for two species which otherwise feel difficult to distinguish.
On a final note, I have not recently checked the distribution of these species, but if my memory serves me well, the expected distribution range of J. lutea was concentrated in QLD. (I'm not too sure! I will look for the research paper if anyone is interested 😊. The two in Whyte and Anderson are from QLD and Grafton (NSW, but close to the border with QLD)). In contrast, one of the sample images of Whyte and Anderson are from Queanbeyan; pretty much just next door to us 😊

I will leave R. gracilis as a suggestion for now for anyone to comment their thoughts before any concrete decisions are made. What do you all think?

I hope these thoughts open a discussion and we can review any changes if they are due! Thank you to CathB and to everyone else for ID so far! Bron, we will keep giving our best IDs 😊. Hopefully we can learn more about our spiders together this way and have some groundwork for future sightings similar to this one.

MichaelMulvaney wrote:

4 Oct 2022

Thanks for the detailed research Yumi. You have convinced me - also Rainer Richter has posted a similar looking spider as Rhombonotus gracilis on INaturalist
https://inaturalist.ala.org.au/observations/101868516
Cheers Michael Mulvaney

Bron wrote:

3 Jan 2023

Thanks Yumi I've been away from CNM for a few months - just catching up a bit during the break. I confirmed your id I hope this is ok... Happy New Year! Cheers Bron

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