Caccothryptus

Caccothryptus is a genus of minute marsh-loving beetle in the subfamily Limnichinae. The genus was first described by entomologist David Sharp in 1902, with C. compactus as the type species.

Taxonomy
Caccothryptus is a genus of Limnichinae, a subfamily of the minute marsh-loving beetles (Limnichidae). Within Limnichinae it belongs to the "Mandersia group" of genera, alongside the much smaller Euthryptus, Mandersia, Pseudothryptus, Resachus, and Simplocarina. These genera share a number of physical features, such as a non-articulated aedeagus (male reproductive organ) without an articulated internal piece ("spiculum") within the median lobe; this distinguishes the genera from the Byrrhinus. The Afrotropical genera Tricholimnichus and Cyclolimnichus are close relatives of the Mandersia group, but lack some distinguishing characteristics in the pronotum.

Taxonomic history
In 1902, entomologist David Sharp described Caccothryptus compactus (found in Martapura, Borneo) in an article in the Entomologist's Monthly Magazine. He described the species as the "largest and most remarkable of the Limnichini" and noted their close resemblance to the Central American genus Euthryptus. Caccothryptus was the first described Limnichinae genus native to Asia.

In 1922 and 1923, Maurice Pic described a new genus he termed Macrobyrrhinus, and placed in it four species of Limnichinae. Harry George Champion considered this genus a synonym of Caccothryptus, in a paper describing three additional species. Pic disregarded Champion's synonymy and placed more species in Macrobyrrhinus in 1928; however, it is now accepted as a synonym. In 2005, Carles Hernando and Ignacio Ribera reclassified one species described by Champion, C. multiseriatus, into a new genus dubbed Pseudothryptus.

Nine years later, Hernando and Ribera published a major redescription and organization of the genus. Previously grouped as seven species, it was reorganized into twenty species in five species groups, classified by similarities in genital shape and some external features. This 2014 revision also classified one of Champion's species, C. laosensis, as a synonym of C. maculosus.

Species and species groups
As of 2021, fourteen new species of Caccothryptus have been identified since the 2014 redescription, all within the compactus and testudo subgroups. The current number of 35 species is likely to increase further, due to a relative lack of studies and material on Asian Limnichidae. Many species are only known from a tiny number of specimens within a small area.

Description
Caccothryptus beetles range from 2.5–5.5 mm in total length. They have ovloid bodies, ranging from brown to black in color, covered in both long and short layers of setae. The head is slightly retracted into the pronotum, with long and narrow eleven-segment antennae covered in short setae. The underside of the abdomens (ventrum) has deep depressions where the long, slender legs connect with the body. Sexual dimorphism is relatively minimal; males of the compactus species have dissimilar anterior claws. Under a microscope, males of all Caccothryptus species have microscopic glandular pores along the central portion of their 4th sternite, while the jaechi and zetteli groups also have these on the 5th.

They generally live in forests, inside piles of water-logged dead wood adjacent to small streams. They are most often collected using light traps.

Range
Caccothryptus species have been found across Southeast Asia, and portions of East Asia and the Indian subcontinent, including the Andaman Islands. Many species are known from a single location, although some (most notably C. maculosus) have been found across a wide swath of territory. The jaechi, zetelli, and rouyeri species groups are only found in Maritime Southeast Asia, while the testudo group is limited to the mainland. Only the compactus group stretches across both.