Spiny Orbweavers (Gasteracantha) and Kin's Journal

Last month Ji Tan et al. published Phylogenetic relationships of Actinacantha Simon, Gasteracantha Sundevall, Macracantha Hasselt and Thelacantha Simon spiny orb-weavers (Araneae: Araneidae) in Peninsular Malaysia in Raffles Bulletin of Zoology.

They illustrate several species and find Gasteracantha paraphyletic with respect to the other three genera.

An interesting read!

Here's the abstract:

Spiny orb-weavers of the genera Actinacantha, Gasteracantha, Macracantha, and Thelacantha are spiders with rigid abdomens and prominent spines that are mostly endemic to Asia. The taxonomy and phylogeny of these spiders are poorly studied due to their intraspecific morphological variations, the rarity of male specimens in collections and the lack of distinctive morphological characters in older descriptions. Therefore, this study has employed for the first time, a multigene approach using three mitochondrial (CO1, CO2 and 16S) and two nuclear-encoded (H3A and 18S) molecular markers to aid in the identification and phylogenetic reconstruction of these spiny orb-weavers collected from Peninsular Malaysia. The genus Gasteracantha as presently circumscribed is not monophyletic, with G. hasselti C. L. Koch, 1837 forming a lineage with A. globulata (Walckenaer, 1841) and M. arcuata (Fabricius, 1793). Our results also revealed two different morphotypes of G. diardi which are morphologically different from G. mengei (Keyserling, 1864). The epigynal structures of G. diardi (Lucas, 1835), G. hasselti, G. kuhli C. L. Koch, 1837, G. mengei, M. arcuata, and T. brevispina (Doleschall, 1857) are illustrated. The morphology of G. diardi and G. mengei is detailed for the first time.

Hi all -- as originally pointed out by @michael-gasteracantha in a comment on the first observation linked below, there is a distinctive spiny orbweaver form currently listed as Gasteracantha mediofusca in the World Spider Catalog that may actually be conspecific with Thelacantha brevispina. It may also be a distinct species, but if so, it apparently belongs in Thelacantha, not Gasteracantha.

Here are four observations that match this form:

• https://www.inaturalist.org/observations/15616648
• https://www.inaturalist.org/observations/16248240
• https://www.inaturalist.org/observations/19754140
• https://www.inaturalist.org/observations/19879640

© 大肚魚, some rights reserved (CC-BY-NC)

The coloration is distinctive. Here is a description from Merian 1911 in original Dutch:

"Het midden-gedeelte van den rug van af den voorsten rand tot en met de achterste stekels donker zwartbruin, rnet twee witte lanwerpige vlekken in het midden, en cene dunne rozenroode streep tusschen beiden; de zijdeljike deelen wit, en aan het voorste gedeelte zeer fijn rozenrood gestreept."

And translated into English via Google Translate:

"The middle part of the back from the front edge to the rear spines of dark black-brown, with two white long spots in the middle, and a thin pink-red line between them; the side parts are white, and very fine rose-red at the front."

Until the taxonomy is revised (which may take several years), I think it makes sense to ID these individuals on iNaturalist as G. mediofusca, since that's how the taxon is currently handled in WSC. Perhaps keeping track of them here could even help solve the long-standing taxonomic mystery.

So as you review Thelacantha observations, keep an eye out for individuals matching mediofusca.

Oh, and until one or more of these observations gets to RG status, I can't figure out how to add any of these photos to the species overview page here on iNat, but hopefully we can do that soon to help build more awareness.