Temnothorax barrettoi

Temnothorax barrettoi was collected from Tai Po Kau Headland, Hong Kong, China, a Site of Special Conservation Interest owing to the presence of natural lowland coastal woodland, which has had a long history of post-World War II reforestation with minimal human disturbance (Kendrick & Barretto 2006). Moreover, the presence of an old pre-war Feng Shui relict woodland also makes the site unique due to the long history of human disturbance elsewhere in Hong Kong (Kendrick & Barretto 2006). One worker of T. barrettoi was found in a leaf litter sample within a patch of secondary forest approximately 250 meters away from the location of the relict forest. Further sampling using winkler extractors and vegetation beating was conducted within the collection site to acquire further specimens of T. barrettoi but resulted in no additional specimens. More information of the site can be found in Kendrick & Barretto (2006).

Identification
Lateral head margin in full face view subparallel; clypeus with longitudinal carinae only in the anterior half; head dorsum with areolate-rugose sculpture; scapes of medium length, not reaching occipital head margin; promesonotum convex; mesosoma dorsal margin straight in lateral view; metanotal groove absent; head, mesosoma and gaster covered in erect, stout setae.

Temnothorax barrettoi would key out to Temnothorax zhejiangensis within Zhou et al. (2010) and shares several morphological characters. Such characters include:
 * the presence of erect setae on the mesosomal dorsum
 * a pair of long slightly downcurved propodeal spines
 * humeri rounded in dorsal view
 * a short petiole peduncle and a petiole that is longer than high

However, a series of substantially and categorically differing morphological characters are present that delimit both species well even without access to type material of T. zhejiangensis. Though our study has this limitation, we justify describing this specimen from Hong Kong as new to science due the considerable uniqueness of the qualitative characters below in comparison to it nearest morphological congeneric species (T. zhejiangensis):
 * the dorsal head sculpture, being distinctly areolate-rugose in T. barrettoi rather than densely punctate in T. zhejiangensis. Punctuae are entirely absent on the dorsal head sculpturing of T. barrettoi and the areolate-rugose sculpturing is unique within Chinese Temnothorax
 * the head sculpturing in T. zhejiangensis also has “fine striations indistinct but present on frons” (Zhou et al. 2010), striations are entirely absent on the head of T. barrettoi
 * the sculpture of the mesosoma dorsum also differs with T. zhejiangensis being “densely punctuate” whereas the sculpture in T. barrettoi is more complex, grading from areolate-rugose anteriorly to more rugose posteriorly, with a gradual increase in punctuation towards the propodeum but not only densely punctuate throughout like T. zhejiangensis
 * the lateral head margins are subparallel in T. barrettoi, converging anteriorly and at the occipital corners, whereas the head margins of T. zhejiangensis are weakly convex throughout
 * the scapes are shorter and distinctly fail to reach the occipital border in T. barrettoi (SL 0.331) but are long and reach the occipital border in T. zhejiangensis (SL 0.39–0.48)
 * in lateral view T. barrettoi has a flat mesosoma dorsum rather than a convex mesosoma dorsum in T. zhejiangensis

Temnothorax barrettoi may also be mistaken for Temnothorax ruginosus. However, both species can be differentiated by the smaller size of T. barrettoi being less than half the size of T. ruginosus (T. barrettoi WL 0.641; T. ruginosus WL (ML in Zhou et al. 2010) 1.80–1.84), as well as the head dorsum sculpture being areolate-rugose rather than coarsely longitudinally rugose in T. ruginosus. Moreover, the lateral head margins are subparallel converging at occipital corners in T. barrettoi but are convex throughout in T. ruginosus.

It was initially thought that this specimen might be a Vombisidris, due to the superficial resemblance with Vombisidris freyae, a species known from the Philippines. Closer examination showed an alternative dental array and the absence of a subocular groove. The high similarity (at least superficially) between this specimen and V. freyae however are initially convincing. Both species share the same head shape, eye positioning and type of sculpture (particularly on the head dorsum), as well as the numerous stout and erect setae across head, mesosoma and metasoma dorsum. Due to the absence of apomorphic characters encountered in Vombisidris, such as the peculiar dental composition and subocular groove, we resulted in the determination of Temnothorax for this specimen instead.

Distribution based on Regional Taxon Lists
Palaearctic Region: China.

Nomenclature

 * . Temnothorax barrettoi Hamer & Guénard, in Hamer et al., 2023: 119, figs. 1, 2, 5 (w.) CHINA (Hong Kong).

Type Material

 * Holotype: CHINA • worker; Hong Kong SAR, New Territories (Tai Po), Tai Po Kau Headland; 22°26′06.0″ N, 114°11′35.52″ E; 70 m a.s.l.; 19–26 Aug. 2022; Matthew T. Hamer and André Ibáñez leg.; leaf litter collected in a line transect of 5 samples each 0.25 m² with silftrate extracted in a Winkler for 7 days; ZRC ANTWEB1010973 [TPK1T2W1-21].