Megisthanus leviathanicus sp. nov. (Parasitiformes: Megisthanidae), the largest known Mesostigmata, a symbiont of the beetle Mastachilus australasicus (Coleoptera: Passalidae)

ABSTRACT

Megisthanus leviathanicus sp. nov. is described from the passalid beetle Mastachilus australasicus from Australia. The adult male is the largest of all known Mesostigmata with one specimen measuring 5.05 mm in length. The sexes are dimorphic: female mites are smaller, have numerous elongate setae, and a lyriform dorsal shield, while the major males have minute dorsal setae and a subovate dorsal shield. Some minor males (n = 4/48) resemble the female in having numerous elongate dorsal setae. Usually only one major male was found on a beetle, but rarely a minor male also occurred, suggesting that a major male defends a beetle and that minor males share access to females. Both sexes had considerable variation in the secondary sclerotization around their dorsal shields. This variation requires some adjustments to the current taxonomy. Herein Megisthanus caudatus is considered a senior synonym of M. brachyurus syn. nov. and M. testudo syn. nov., as M. brachyurus is based on a female without secondary sclerotization and M. testudo on the male of M. caudatus. The Australian species Megisthanus thorelli, and the North American species Megisthanus floridanus, are diagnosed. The diagnostic character states for megisthanid species are explored, especially the female’s internal genitalia.

http://www.zoobank.org/urn:lsid:zoobank.org:pub:FB6B6509-64A6-4454-8B58-F412FA2833C1

KEYWORDS:

• Antennophorina
• taxonomy
• sexual dimorphism
• female mimicry
• gigantism

Acknowledgements

I am very grateful for the photography of Mr Jeff Wright (Figure 1) and Mr Geoff Thompson (Figure 2), for collecting permits from the Queensland Parks and Wildlife Service, for exemplary help with literature from Dr Bruce Halliday, and for assistance with collecting, advice and helpful comments from Dr David Evans Walter. This project was funded by the Australian Biological Resources Study, grant number RF215-07.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This project was funded by the Australian Biological Resources Study, grant number [RF215-07].