Figures 35-40, Map (Figure 1) #52

Cosmophasis thalassina, the type species for Cosmophasis, is well-known across the tropical north of Australia and neighboring Papua (Figure 1; Żabka & Waldock 2012; Whyte & Anderson 2017), but there is some question regarding its distribution to the north and west, in Sunda. The females appear to be quite variable in colouration. Little is known of the biology of this species, other than a single observation of what appears to represent a female of this species feeding on butterfly eggs in Queensland (Donovan & Hill 2017). C. L. Koch (1846) described this species from a male collected on Bantan Island, just southeast of Singapore (Appendix 4).

Diagnosis. No type specimens have been found, so our ability to identify this species relies primarily on the original description by C. L. Koch (1846; see Figure 4:1 and Appendix 4), and its subsequent redescription by Żabka & Waldock (2012). In Australia, males can be readily separated from C. baehrae by their lack of a lateral black stripe below each ALE. Behind a white face that extends partly to the sides of the carapace, each male has a short but thick black crest above the anterior eye row, a second black band extending between the PLE, and a third black band crossing the rear of the carapace. Otherwise the carapace is covered with mostly iridescent green, but perhaps iridescent blue, scales, with the sides of the carapace covered with multicoloured gold to violet scales.

The opisthosoma is generally black, with a white marginal band extending around the sides from the front, and a tract of bright iridescent scales at the median. On the venter are the three pairs of large white spots seen in other Cosmophasis species. The pedipalps are white with black tips, a feature shared with male C. baehrae and perhaps other species. Genitalia are well-described by Żabka & Waldock (2012). The male pedipalp is not unusual. The origin of the embolus is near the 160° position, depending somewhat on how it is photographed or drawn, and the distal cymbium is quite short. Although females vary greatly in colouration, their genitalia may suffice for their identification.

According to Żabka & Waldock (2012), C. micans (L. Koch 1880) from "Cape York " is a good species, but they could find no specimens of this Australian species and none may exist, perhaps not even in nature. The female of this species is not known. There is little in the description of the male, and the drawings that accompany this description (Appendix 3), to suggest that this is anything other than a male C. thalassina. However, according to L. Koch, the AME of this male are separated from the lower edge of the carapace (the bottom of the clypeus) by almost twice their length. This is remarkable, something not seen in other Cosmophasis. But Koch's drawing fails to show the flexible articulation of the chelicerae between the clypeus and the chelicerae, and this may have been misinterpreted by the artist. Because of this articulation, the AME of C. thalassina, at least in a preserved specimen, can be separated from the chelicerae by something close to two times their diameter. In a revision of the genus C. micans might be declared a nomen dubium.

Although C. thalassina is widely-distributed and both the male and female have been described, it can still be difficult to identify this spider in the field. In large part this is due to its similarity with C. umbratica, or perhaps to some other species with a similar appearance that have yet to be described from life. The living males illustrated by Żabka & Waldock (2012, fig. 60A-B) look like C. baehrae. The examples that we show here (Figures 35-40) agree with the original description of C. thalassina, as well as the excellent photographs of that species recently published by Whyte & Anderson (2017).