The male and female have a rounded abdomen.
There are no projecting humps on the back of the abdomen.
Male Zephyrarchaea barrettae bears a proximal brush and an additional comb of hairs on the front of its chelicerae. The described female lacks these accessory hairs. The male also has a reddish-brown dorsal abdominal plate extending over the anterior two-thirds, while the female’s abdomen is variably beige-grey.
In the 2012 description, the name-bearing male measured 3.13 millimetres in total length and the detailed female specimen 3.64 millimetres. Their first-leg femora measured 2.19 and 2.31 millimetres, respectively. The male was collected in August 2008 and the female in February 2009, near the summit of Talyuberlup Peak. Both came from elevated leaf litter beneath sedges. Although only a few millimetres long, these specimens preserve specific differences in jaw hairs and abdominal covering, alongside precise measurements of their leg segments.
An extinction-risk assessment has not been added yet.
The 2012 description treated barrettae as a short-range endemic of the western Stirling Range National Park, Western Australia, with a maximum total range below 10 square kilometres at that time. The authors identified fire, dieback disease affecting montane vegetation, and climate change as potential threats. Summit vegetation and its leaf-litter habitats therefore form the setting for conservation concerns about this spider.
The Western Australian South Coast regional conservation plan of December 2025 proposes biennial post-fire habitat surveys for this species and four other assassin spiders to assess whether they return after fire.