Trigonopterus

Trigonopterus is a genus of flightless weevils placed in the Cryptorhynchinae of Curculionidae. It is distributed in the area between Sumatra, Samoa, the Philippines, and New Caledonia. About 90 species had been formally described until March 2013, when a single paper more than doubled this number, agreeing with previous studies and a systematic barcoding study that many more species have yet to be described. As of March 2019, there were 444 described species. The center of its diversity appears to be New Guinea where 51 or more species can be found in a single locality. Many of them are very similar to each other, but male genital characters and DNA barcoding allow a safe identification. In January 2016 a paper was published that revised the Australian species within this genus. That paper described 24 new species and indicated the potential for more research into undescribed Australian species within this genus. In April 2016 a paper was published that described four new species in this genus from the island of New Britain. The paper postulated that more species of this genus presently unknown to science may exist on the island. It emphasised the importance of prioritising further research due to the ongoing destruction of the habitat of these species. In March 2019 a further paper was published describing 103 new species from Sulawesi, where only one species (T. fulvicornis) had previously been recorded. The genus can be diagnosed among wingless cryptorhynchine weevils by the absence of a metanepisternum and by a synapomorphic structure of the tarsus with minute claws and a deeply incavated articulation of tarsomere 4. The metathoracic spiracle located externally at the side of the metaventrite is a unique feature and may ensure sufficient respiration during thanatosis. Trigonopterus species inhabit primary tropical forests, both on foliage and edaphic in the litter layer. They have a marked tendency to endemism with many species only known from a single locality. Their primary defence against predators is apparent death or thanatosis. An animated 3D model of a Trigonopterus weevil reveals a number of mechanisms to maintain a stable defensive position. The species Trigonopterus oblongus (Pascoe, 1885) is found in Papua. It became notable in July 2011 when examination of the anatomy of the weevil revealed the first instance of a biological screw joint. T. oblongus is just 4 millimetres (0.16 in) long and can fold their legs below their body. The biological screw joint is just 0.5 millimetres (0.020 in) in size. This discovery was made by Alexander Riedel of the State Museum of Natural History Karlsruhe and by Thomas van de Kamp of the Karlsruhe Institute of Technology.