Oristicta filicicola Tillyard, 1913

Burwell, Chris J., 2017, A second species of Oristicta Tillyard (Odonata: Isostictidae), Zootaxa 4323 (1), pp. 83-95 : 85-89

Oristicta filicicola Tillyard, 1913

In the description of O. filicicola Tillyard (1913) did not describe the structure of the pronotum and thus did not mention any process on the posterior lobe of the pronotum, whereas Lieftinck (1951) described the pronotum of P. interposita as unarmed, repeating what he already specified in the diagnosis of the genus.

No mention was made by both authors of a very subtle banding on the femora.

Only Tillyard mentioned that there is sometimes also a brownish cloud on dorsal surface of S2 while only Lieftinck mentioned a dark (probably black) stripe on the mesepimeron.

These inconsistencies were reason enough to re-check the primary types of O. filicicola and P. interposita and representative material that was currently assigned to the genus Oristicta .

Fortunately detailed photos of the lectotype of O. filicicola ( Figs 5–12 ) were made available. They clearly show the characters given in the original description ( Tillyard 1913) and in addition prothoracic horns ( Fig. 9 ) which were also found, without exception, in all male non-typical specimens ( Fig. 4 ) studied as listed below ( Table 1).

The holotype of P. interposita , a very immature specimen in bad condition ( Fig. 13 ), did not conclusively show presence or absence of pale subapical patches or a pale cloud on S2, or present a clear image of the shape of the anal appendages. However, a posterolateral process on the left side of the posterior lobe of the pronotum was detected (as already mentioned in Watson et al. (1991)); it was found strongly bent laying parallel to the posterior margin of the posterior lobe, whereas the horn on the right was not detected (possibly broken off). Even though considerable darkening in the mesepimeron is noticeable and the dark dorsal patch in S2 appeared uninterrupted by pale patches or a pale cloud, characters rather rare in the non-typical material of O. filicicola studied, the presence of the posterolateral horn on the posterior lobe of the pronotum and subtle characters like the feeble banding of the femora strongly indicate that it is conspecific with O. filicicola . The superior anal appendages, with some twisting apparent, are also more similar to O. filicicola than the illustration in Lieftinck (1951) makes them appear. Thus the taxonomic decision of Watson et al. (1991) to regard P. interposita as a junior synonym of O. filicicola is supported.

Although the studied material shows some variability, even in the shape of the male inferior anal appendages ( Figs 19–22 ), the differences are small, often hard to detect and do not seem to be consistent, clear-cut or strictly geographically coordinated. The only character that may be interpreted as separating possible geographical infraspecific taxa appears to be size. Specimens from distinctly north of Cooktown are smaller (Hw 18.5–20.0 mm [N=10] and see Figs 4a , 19–20 ) than specimens from further south (Hw 20.5–23.0 mm [N=10] and see Figs 4b , 21– 22 ). However, because of agreement of all material in general appearance and the males consistently having the posterolateral horns on the posterior lobe of the prothorax ( Figs 4a, 4b ), it does not appear justified or feasible to distinguish subspecies. Oristicta filicicola is considered to be a monotypic species, strictly tropical with available records ranging from Hammond Island (10.5°S) at the tip of Cape York in the north to Paluma (19°S) in the south (Fig. 41).

Figures

FIGURES 5 – 9. Oristicta filicicola Tillyard, Lectotype male NHMUK 010730568: (5) Labels; (6 – 7) Habitus: (6) dorsal; (7) lateral; (8) head, thorax and anterior abdominal segments, dorsal; (9) posterior lobe of pronotum, dorsal. Photos by Ben Price.

FIGURES 10 – 12. Oristicta filicicola Tillyard, Lectotype male NHMUK 0 10730568, anal appendages: (10) dorsal; (11) ventral; (12) lateral. Photos by Ben Price.

FIGURES 1 – 4. Oristicta filicicola Tillyard, male: (1 – 3) modified from Tillyard (1913): (1) hindwing; (2 – 3) anal appendages: (2) right side, dorsal; (3) lateral; (4) posterior lobe of pronotum, dorsal: (a) from Iron Range; (b) from Lizard Island nr Cooktown.

FIGURES 13 – 15. Phasmosticta interposita Lieftinck, Holotype male: (13) Habitus, lateral. Photo by J Van Tol; (14 – 15) Modified from Lieftinck (1951): (14) wings; (15) anal appendages, lateral.

FIGURES 19 – 22. Oristicta filicicola Tillyard, male, anal appendages, dorsal: (19 – 20) from Iron Range; (21 – 22) from Lizard Island. Photos by John Martin.