Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Hexapoda
Class: Insecta
Order: Coleoptera
Suborder: Polyphaga
Superfamily: Scarabaeoidea
Family: Lucanidae
Subfamily: Aesalinae
Tribe: Ceratognathini
Genus: Mitophyllus
Species: M. arcuatus
Binominal name: Mitophyllus arcuatus

Mitophyllus arcuatus is a recently described beetle in the stag beetle family Lucanidae. The Mitophyllus genus of beetle endemic to New Zealand. Mitophyllus arcuatus is found in the northern half of the North Island. It has not been collected above 500 m. 
Mitophyllus arcuatus is a small stag beetle with a  black and brown variegated pattern. The antennae are short with three prongs.
Males have a body length of (including mandibles) 8.6–11.8mm, females (including mandibles) 7.8–10.6 mm.
Nothing is known about the food of the adults but it is likely to be nectar. 
Mitophyllus arcuatus spend most of their lives in the larval stage feeding on the dead and rotten wood of a variety of hosts, one of them being Kiwifruit.

1-Mitophyllus arcuatus Stag beetle-003.jpg

1-Mitophyllus arcuatus Stag beetle-001.jpg

A photo of the head and pronotum of a male Mitophyllus arcuatus.1-Mitophyllus arcuatus Stag beetle-004.jpg

The beetle's three-pronged antennae
1-Mitophyllus arcuatus Stag beetle.jpg

There is another NZ stag beetle Mitophyllus irroratus that looks similar but can easily be identified by the differences in the shape of their mandibles. Mitophyllus arcuatus mandibles have a circular gap between them when closed. Mitophyllus irroratus jaws close with a rectangular gap between them. The differences between females mandibles are more subtle.
Male mandibles
Mandibiles stag beetles.jpg

1-collection map.jpg  

Thanks to Wikipedia for text and information: