Several phragmotic species in the ant genus Carebara Westwood, 1840 with a cephalic shield are known from the Old World, but species with an anteriorly truncated head seem to be unknown until now. A new species, resembling the phragmotic workers of the ant genus Colobopsis, is here described as Carebara colobopsis Hosoishi & Yamane, sp. nov., based on major and minor worker found in Cambodia. This new species is similar to Carebara acutispina (Xu) and C. obtusidenta (Xu) in some important characters, but distinguished from the latter two by distinct metanotum and deep groove in front of metanotal disc in the major worker, and longer head and deep metanotal groove in the minor worker. This is the first confirmed record of a truncated phragmotic head in the major worker of the genus Carebara. We propose the Carebara acutispina species group to include all the three species, present a diagnosis of this group, and provide a key to species based on the major and minor worker castes.
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