Maratus avibus Jürgen C. Otto & David E. Hill 2014, new species

Maratus avibus new species

Type specimens. The holotype male (♂ #1) and two paratype males (♂ #2, ♂ #3) were collected near the ruins of the old 'Hill Springs' homestead at Cape Arid National Park in Western Australia (33°58'12.3"S, 123°13'15.6"E, 15 OCT 2013, Jürgen Otto and David Knowles coll.). All will be deposited in the Western Australian Museum, Perth.

Etymology. The species group name (avibus, Latin, noun in apposition to the genus name, English translation birds) refers to the appearance of two facing birds on the extended opisthosomal fan of males.

Diagnosis. Only one other member of the mungaich group lacks a dark central spot or patch on the dorsal opisthosoma or fan of the male, M. caeruleus Waldock 2013, a species known from two specimens collected on Middle Island (Recherche Archipelago). The distinctive pattern of scales on this fan, including patches that resemble a pair of birds facing each other, readily distinguishes M. avibus from that species (Figure 1). Waldock's (2013) measurement (7.89 mm length excluding spinnerets) would make M. caeruleus a much larger species than M. avibus, although this difference is not so significant if the scale bars in her drawings are correct.

Description of male (Figures 2-6). The holotype and two paratype specimens range from 4.44-4.50 mm in body length, not including the spinnerets. With the protruding spinnerets, the holotype specimen is 4.66 mm in length. The carapace, except for scale or setal fields, is glabrous and dark black-brown (more black in life). The chelicerae are also dark black-brown, of average size for the genus. Long white setae cover the clypeus, extending over the median and down, above the top of the chelicerae, from both sides. The eye region is covered with grey scales, except for red-brown scale bands at the lateral margins, and a more-or-less distinct 'm' shape comprised of red-brown scales at the center, with its base at the line between the rear margins of the PLE (Figure 2:3,4). The PME are closer to the PLE than to the ALE. Behind the eye region, an irregular median band of white setae extends about half-way to the rear margin of the carapace, surrounded on either side by scattered red-brown scales. A thick marginal band of white scales is present at each lateral margin of the carapace.

The opisthosoma bears a prominent dorsal plate with extensible flaps that, when not used in display, are wrapped around the lateral sides to meet or to overlap at the venter. At the anterior of this plate long, white, erect setae project toward the carapace. The plate itself (Figure 4), when not expanded, displays a relatively uniform, dense cover of matte to slightly iridescent grey to grey-green scales, with a single more-or-less interrupted transverse bar of orange scales toward the rear. Posterior to the orange band is a band that consists of highly iridescent blue-purple scales that may change colour depending on the direction of incident light. When the flaps of this plate are fully extended in display, more varied markings can be seen. These resemble a pair of birds facing each other, with four bright iridescent blue or purple spots surrounded by black, with a crown of red forming the 'head' of each bird. From each 'head', a black 'neck' bounded medially by red-orange scales extends toward the front, an 'upper beak' comprised of a large, oval patch of iridescent dark green scales extends toward the median, and a 'lower beak' of redorange scales extends toward the median. The 'neck' of this bird-like figure is surrounded by iridescent blue-purple scales that are more intensely coloured than those in the centre of the fan.

The ventral opisthosoma is grey-white, bearing many long white setae. The posterior, including the anal tubercle with its tuft of white setae (typical for Maratus), and the grey, normal-sized spinnerets below this, can be inflated or extended well beyond the posterior margin of the fan (Figure 2:2), most likely the result of recent feeding. The sternum is grey (or brown in preserved specimens) with long white setae extending to the rear, the labium and endites, like the coxae, translucent grey (or white in preserved specimens).

Legs I and II are about the same length, much shorter than legs III and IV. Legs III are the longest. Coxae, trochanters, and proximal femura of all legs are translucent or light grey in living spiders, white in preserved specimens, mottled with two or three dark spots. In living spiders, legs I,II,IV are dark brown distally from the proximal femur, ending in light-brown or translucent tarsi, and irregularly ringed with long white setae. The elongated femora of legs III are lighter above, with a fringe of long white setae and covered with white scales, but black in the front and back, and below. Patellae, tibiae, and metatarsi III are fringed below with long white, ivory, or brown setae. On other surfaces patellae, tibiae, and metatarsi III are irregularly covered with ivory and brown scales. Tarsi are densely covered with long white setae, extending dorsally over the foot pads.

Proximal segments of each pedipalp bear long white setae, but mostly the dorsal pedipalp bears a dense cover of long ivory setae. The pedipalp (Figure 6) is typical for the genus. Apart from a 'toothed edge' on the outer ring of the embolus, a feature that could easily be overlooked, there is little to distinguish this species from other members of the mungaich group.

Fan dance of the male. When placed near a female Maratus, a male M. avibus would face this female, extend and elevate the opisthosomal fan in a manner typical of the genus, then display in a distinctive manner that has not been recorded for any other species (Figures 7-10). The extended fan was 'bracketed' by the extended legs III, which were held just in front of the fan with tarsi brought together so that the legs almost enclosed the fan as seen from the front. This raised bracket resembled a hexagon, with five sides enclosed, open only at the top (set position; Figures 7-8). We recorded two different modes of display with the fan in this position (Otto 2014). In the slow mode (Figure 9), the male rotated the fan to one side and then to the other, not moving pedipalps or legs. This began with rotation of the centered fan to one side over ~0.5s, followed by much faster (~0.05s or less) return to the centered position. Rotation to the opposite side could begin ~0.5s later. Just before the fan was returned to the centered position, it was rotated (or depressed) slightly to the rear, movement resulting in a flash or sudden increase in the intensity of light reflected from the iridescent scales of the fan toward the front of the male. The fast mode of display (Figure 10) was observed at the onset of an encounter with a female. Here the set position alternated with bouts of rapid vibration of the fan mostly toward the rear, bilateral movement of legs III (pinch), or a combination of the two. Speed of vibration was not measured, but the period of each cycle between set and vibrating positions was ~0.08s. All vibration within each cycle occupied no more than a single 0.04s frame, and these cycles continued in one clip for ~4s (~50 cycles).

Habitat and distribution. These spiders were found on or near the ground at Cape Arid National Park (Figure 11). They are known from only the single, type locality (Figure 12:2, locality 7).